(199)enzyme 2011
DESCRIPTION
Enzypes for MBBS students of first year.I am very thankful to all the colleaguesTRANSCRIPT
ENZYMOLOGY
Contribution of Scientists. Definitions. Mode of Action of Enzymes. Factors Influencing Enzyme Activity. Enzyme Inhibition. Regulation of Enzymes. Diagnostic Importance of Enzymes. Therapeutic Use of Enzymes.
ENZYMES
© 2007 Paul Billiet ODWS
BERZELIUS 1835 Starch. Hydrolysis.
KUHNE 1878
Enzyme mean yeast.
EDWARD BUCHNER
Sucrose to Ethanol
ENZYMES
© 2007 Paul Billiet ODWS
EDWARD BUCHNER N.P.1907
ARTHUR HARDEN N.P. 1929
JAMES SUMNER N.P. 1946
JOHAN NORTHROP N.P. 1946
WILHELM OSTWALD N.P. 1909
WARBURG N.P. 1970
ENZYMES
DR.K.S.SODHI,M.D.
PROFESSOR
BIO-CHEMISTRY
MMIMS&R MULLANA AMBALA.
© 2007 Paul Billiet ODWS
A GOOD TEACHER IS ALWAYS A GOOD
CATALYST IN STUDENTS LIFE.
ALWAYS A GOOD CATALYST IN STUDENTS LIFEALWAYS A GOOD CATALYST IN STUDENTS LIFE
DISTRIBUTION OF 17 HORSES OLDMAN AND THREE SONS. DISTRIBUTION OF HORSES. ELDER ½ MIDDLE 1/3 LITTLE 1/9
ENZYMES
© 2007 Paul Billiet ODWS
EDWARD BUCHNER N.P.1907
ARTHUR HARDEN N.P. 1929
JAMES SUMNER N.P. 1946
JOHAN NORTHROP N.P. 1946
WILHELM OSTWALD N.P. 1909
WARBURG N.P. 1970
Vitro and Vivo Reactions
Starch into glucose. Boil for 2 hours in conc Hcl
For digesting meat need strong acid and long time
Starch is converted in to glucose in Minutes in the presence of enzymes.
With in hour at pH 7.4
DEFINITIONSHOLOENZYMES ( APOENZYMES+CO ENZ.)APOENZYMES; SINGLE POLYPEPTIDECHAIN,MORE THAN ONE CHAIN,MULTI-ENZYME COMPLEX.Co-ENZYMES: Non Protein (VITAMINS)METAL-ACTIVATED ENZYMES.(Zn,Cu,Fe,Mg,K,Ca etc.)ZYMASE: Active without modificationZYMOGENS: Pro Enzymes eg.Trypsinogen to trypsin
ISO-ENZYMES: Physically distinct perform same function.
RIBOZYMES: Small ribonuclear particles. ENDOENZYMES: Produced in the cell.
Function inside the cell. EXOENZYMES: Produced inside the cell.
Act outside the cell.
METALLO ENZYMES: Contain metal ions as essential component.
HOUSE KEEPING ENZYMES: Levels of Enzymes can not be controlled. Always present in cell.
ADAPTIVE ENZYMES: Regulated by genes. Conc.increase or Decrease.
KEY ENZYMES :Regulatory eg HMG-CO.A HYBRID ENZYMES :Produced by genetic fusion.
COFACTORS An additional non-protein
molecule that is needed by some enzymes to help the reaction
Tightly bound cofactors are called prosthetic groups
Cofactors that are bound and released easily are called coenzymes
Many vitamins are coenzymes
Nitrogenase enzyme with Fe, Mo and ADP cofactors
CO-ENZYMES Essential for Biological activity. Low molecular weight, Organic in nature Non protein in nature. .Combine loosly with Enzyme &separate later. Thermostable. Help in group transfer. Bind to apoenzymes. Eg.NAD, NADP, FMN, FAD, Biotin, Lipoic Acid,
Pyridoxal Phosphate,etc. (Vitamins) Co-enzyme separate from apo-Enz after reaction. Can be separated by Dialysis.
Co-Enzymes can be divided into two groups. A.Oxidoreductases.NADH.NADPH,FAD.
B. Transfer Groups. Thiamine-Hydroxyl group. Pyridoxal phosphate-Amino group Tetrahydrofolate-one Carbon Biotin-Carbon dioxide.
TABULAR FORM SHOWING CO.E
Enzyme structure Enzymes are proteins
They have a globular shape
A complex 3-D structure
© 2007 Paul Billiet ODWSHuman pancreatic amylase
STRUCTURE1.MONOMERIC: Single Peptide.
2.OLIGOMERIC: Many peptide Chains.
3.Multienzyme Complex:
Fatty Acid Synthase
LDH Complex.
Prostaglandin Synthase Complex.
ENZYMES UNITS KINGARMSTRONG. SOMOGY. REITMAN FRANKEL. SPECTROPHOTOMETRIC. KATAL. INTERNATIONAL UNIT.
ENZYMEZS ESTIMATED FROM: WHOLE BLOOD, SERUM, PLASMA. RED BLOOD CELLS. C.S.F. URINE. SWEAT. SALIVA. SEMEN. AMNIOTIC FLUID. Tears.
PLASMA ENZYMES FUNCTIONAL PLAMSMA ENZYMES. eg.
LIPOPROTEIN LIPASE, BLOOD CLOT DISSOLVING ENZYMES etc.
NON FUNCTIONAL PLASMA ENZYMES. eg: SGOT, SGPT,AMYLASE,CPK,LDH,LIPASE,ACID-PHOSPHATASE,ALKALINE PHOS., CERULOPLASMIN etc.
NATURE OF ENZYMES
Soluble, Colloidal, Organic Catalysts Formed by Living Cells ,Specific in
action, Protein In Nature ,Inactive at Zero degree centigrade ,Destroyed by moist heat at 100 degree centigrade (Heat Labile), Huge in size, small Active Site, Used for Treatment.
DIFFERENCE BIO-CATALYST:
Enzymes, protein in nature except ribozymes, More specific, more efficient and slight change in structure alter its action.
CATALYST:
Inorganic, less sp., less efficient and no change in structure.
THE ENZYMES SPEAK
“WE ARE THE CATALYSTS OF THE LIVING WORLD? PROTEIN IN NATURE, AND IN ACTION. SPECIFIC, RAPID AND ACCURATE; HUGE IN SIZE BUT WITH SMALL ACTIVE CENTRE; HIGHLY EXPLOITED FOR DISEASE DIAGNOSIS IN LAB CENTRES AND ALSO USED FOR TREATMENT.’’
TISSUES BRAIN,HEART,LIVER,KIDNEY,MUSCLE
MUSCLE→ ← HEART
→LIVER ←STOMACH
BRAIN
← KIDNEY
←INTESTINE
COMPARTMENTATION
MITOCHONDRIA: Enzymes of: E.T.C, TCA Cycle, Beta Oxidation, Urea Cycle,
Pyruvate to Acetyle Co-A. CYTOSOL: Glycolysis, HMP Shunt, Fatty
Acid Synthesis, Glucogenesis and Glycogenolysis.
NUCLEUS: DNA Synthesis, RNA Synthesis and Histones etc.
LYSOSOMES :
FUNCTIONS OF ENZYMES
1. Catalyse thousands of reactions. 2. Digestive Enzymes help in Digestion. 3. Lysosomal Enzymes destroy in cell. 4. Lysozymes are bacteriocidal, local
immunity. (TEARS) 4. Detergents 5. Textile. 6. Leather Industry.
What is a Ribozyme?
1) Enzyme
2) Ribonucleic Acid
NOT PROTEIN
1989 Nobel PrizeIn Chemistry
Sid Altman Tom Cech
RIBOZYMES
Small ribonuclear particles. Contain rRNA. Highly substrate specific. Used in Intron splicing,pre RNA to RNA Peptidyl
Transferase. Many ribozymes have hair-pin or hammer head
shaped active centre &require Divalent Mg++ Catalyse reaction on phosphpdiester bonds of other
RNA
Ribozymes Have following Drawbacks. Not as efficient as protein catalysts( In RNA
there are 4 nucleotides, in amino acid are 20 in number.
Act once only in chemical event,protein enzymes are reused several times.
Rate of catalytic activity is slower. Synthatic Ribozymes are having better
catalytic activity(Cleave infectious Virus) Used in Gene therapy.
ABZYMES
Artificially synthasized catalytic antibodies against Enz. Sub. Complex in transition state of reaction. CATMAB (Catalytic Monoclonal Antibody).
Sometimes natural abzymes are found in blood,eg.antivasoactive intestinal peptide autoantibodies.
Useful in diseases viz.abzyme against gp120 envelop protein of HIV may prevent virus entry in to the host cell.
Structure : As with proteins, we consider...
Primary: GGCCGAACUGGUA
Secondary:
Tertiary:
Secondary StructureWatson-Crick Base Pairing Helix Formation
B-DNA RNA
RNA usually assumesA-form helices…
Small pore along helical axis
“Rungs” stack obliquely to axis
A-DNA
Secondary Structure
Conserved base-pairing interactions result in...
• Three “stem” regions
• Uridine-containing turn
• An “augmenting helix” joining stems II and III
Ribozyme vs. tRNAPhe
folding
Tertiary Structure
The Future of Ribozymes
In Vitro Molecular Evolution of RNA
High Throughput Screening
Ribozyme-Based Therapies
+
In Clinical Trial...
HIV Gene Therapy...Bone Marrow Sample
Treat Stem Cells with Retroviral Vector
Re-Implant Treated Cells
Encodes Gene for anti-HIV Ribozyme
ACTIVE SITE OF RIBONUCLEASES It lies in a hydrophobic cleft. 7th Lysine 41st Lysine on one side and 12th
Histidine and 119Histidine on the opposite side.(URIDYLIC ACID)
Peptidyl transferase (chain Elongation) Removal of Introns.
The Substrate
The substrate of an enzyme are the reactants that are activated by the enzyme
Enzymes are specific to their substrates The specificity is determined by the active
site
© 2007 Paul Billiet ODWS
PRODUCT
Substrate in the presence of Enzyme is converted in to product.
The reaction can be Reversible or Ir-reversible.
The increase in product concentration can cause inhibition and stop the reaction in the forwaed direction.
ABBREVIATIONS
ENZYME [E] SUBSTRATE [S] PRODUCT [P] Enz. Sub. Complex [ES] INHIBITOR [I] Enz.+Inh. Complex [EI] Enz.+Sub.+Inh. [ESI]
Enzyme Stabilizes Transition State
S
P
ES
EST
EP
ST
Reaction direction
Energy change
Energy required (no
catalysis)
Energy decreases (under
catalysis)
Sub.(S) Prod. (P)Enz(E)T = Transition stateV=rate of change of S to P/mt.
Adapted from Alberts et al (2002) Molecular Biology of the Cell (4e) p.166
Control Points of Gene Regulation
Prokaryotics
DNA
ribosomemRNA
proteins
Post-translationalcontrol Eukaryotics
proteins
cap5’ 3’
tail
mature mRNA
DNA
5’3’process
mRNA
Juang RH (2004) BCbasics
Translation
Activity
Proteolysis
Transcription
RNA ProcessingRNA Transport
RNA Degradation
ACTIVE SITE OF ENZYME
Chymotrypsin His(57)Asp(102)Ser(195) Trypsin Histidine,Serine Phosphoglucomutase Serine Carboxypeptidase
Histidine,Arginine,tyrosine Aldolase Lysine
Active Site Avoids the Influence of Water
Preventing the influence of water sustains the formation of stable ionic bonds
-+
Active Site Is a Deep Buried Pocket
Why energy required to reach transition stateis lower in the active site?
It is a magic pocket
(1) Stabilizes transition(2) Expels water(3) Reactive groups(4) Coenzyme helps
(2)
(3)(4)
(1)CoE
+
-
Juang RH (2004) BCbasics
The active site: Is a region within an
enzyme that fits the shape of molecules called substrates.
Contains amino acid R groups that align and bind the substrate.
Releases products when the reaction is complete.
Active Site
ACTIVE SITE
Generally the active site is situated on the cleft of the Enzyme.
Binding of substrate to active site dependends upon the presence of sp. Groups or atoms at active site.
During binding these groups,realign themselves so as to fit the substrate.
The substrate bind to active site by non co-valent bonds.(Hddrophobic in nature)
Amino acid that make or break bonds called catalytic group.
ACTIVE SITE
MECHANISM OF ACTION
INDUCE FIT MODEL.(KOSHLAND’S) LOCK AND KEY MODEL. (FISHER’S
TEMPLATE THEORY)
The Induced Fit Hypothesis Some proteins can change their shape
(conformation) When a substrate combines with an enzyme, it
induces a change in the enzyme’s conformation The active site is then moulded into a precise
conformation Making the chemical environment suitable for the
reaction The bonds of the substrate are stretched to make
the reaction easier (lowers activation energy)
© 2007 Paul Billiet ODWS
Induced-fit Model
In the induced-fit model of enzyme action: The active site is flexible, not rigid. The shapes of the enzyme, active site, and
substrate adjust to maximum the fit, which improves catalysis.
There is a greater range of substrate specificity.
The Lock and Key Hypothesis Fit between the substrate and the active site of the enzyme is
exact Like a key fits into a lock very precisely The key is analogous to the enzyme and the substrate
analogous to the lock. Temporary structure called the enzyme-substrate complex
formed Products have a different shape from the substrate Once formed, they are released from the active site Leaving it free to become attached to another substrate
© 2007 Paul Billiet ODWS
Lock-and-Key ModelIn the lock-and-key model of enzyme action: The active site has a rigid shape. Only substrates with the matching shape can fit. The substrate is a key that fits the lock of the
active site. Rigid structure could not explain flexibility
shown by enzymes
CLASSIFICATION 1.OXIDO-REDUCTASE.transfer of hydrogen or
addition of oxygen.Eg.LDH 2.TRANSFERASE.Eg.Aminotransferase. Hexokinase. 3.HYDROLASE.Cleave bond adding water Eg. Acetyl choline estrase. 4.LYASE.Cleave without adding water (Aldolase) 5.ISOMERASE. 6.LIGASE.Acetyl co-A
carboxylase,Glu.Synthatase,PRPP Synthatase.
FACTORS AFFECTING ENZYME 1.SUBSTRATE CONCENTRATION. 2.ENZYME CONCENTRATION. 3.TEMPERATURE. 4.pH. 5.EFFECT OF PRODUCT CONC. 6.PRESENCE OF ACTIVATORS 7.INHIBITORS. 8.EFFECT OF TIME.
FACTORS………………..
9.EFFECT OF CLOSE CONTCT. 10.OXIDATION OF ADD.GROUPS. 11.EFFECT OF LIGHT. 12.EFFECTS OF RADIATIONS. 13.PRESENCE OF REPRESSOR
DEPRESSOR 14. ANTIZYMES.
Substrate concentration: Non-enzymic reactions
The increase in velocity is proportional to the substrate concentration
Reaction velocity
Substrate concentration
Substrate Concentration
The rate of reaction increases as substrate concentration increases (at constant enzyme concentration).
Maximum activity occurs when the enzyme is saturated.
Substrate concentration: Enzymic reactionswhen[ s] conc. Is increased velocity increases in the initial phase (Vmax.),but flatten afterward.
Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied.
If you alter the concentration of the enzyme then Vmax will change too.
Reaction velocity
Substrate concentration
Vmax
© 2007 Paul Billiet ODWS
Salient Features of Km
Km is sub. Conc.at ½ the max. velocity It denotes that 50% of Enzyme mol.are bound with sub.at
particular sub. Conc. Km is independent of Enzyme conc.If Enz. Conc. Is doubled, the
Vmax will be double but km will remain same. Km is signature of Enzyme. Affinity of Enz. Towards its substrate is inversely related to the
dissociation constant(smaller the dissociation greater the affinity. Km denotes affinity of enzme for substrate.lesser the Km more
the affinity.
Enzyme Concentration
The rate of reaction increases as enzyme concentration increases (at constant substrate concentration).
At higher enzyme concentrations, more substrate binds with enzyme.
End point reaction.
The effect of temperature
For most enzymes the optimum temperature is about 30°C
Many are a lot lower, cold water fish will die at 30°C because their enzymes denature
A few bacteria have enzymes that can withstand very high temperatures up to 100°C
Most enzymes however are fully denatured at 70°C
© 2007 Paul Billiet ODWS
Enzymes: Are most active at an
optimum temperature (usually 37°C in humans).
Show little activity at low temperatures.
Lose activity at high temperatures as denaturation occurs.
Temperature and Enzyme Action
The effect of temperature
Temperature / °C
Enzyme activity
0 10 20 30 40 50
Q10 Denaturation
The effect of temperature
Q10 (the temperature coefficient) = the increase in reaction rate with a 10°C rise in temperature.
For chemical reactions the Q10 = 2 to 3(the rate of the reaction doubles or triples with every 10°C rise in temperature)
Enzyme-controlled reactions follow this rule as they are chemical reactions
BUT at high temperatures proteins denature The optimum temperature for an enzyme controlled
reaction will be a balance between the Q10 and denaturation.
The effect of pH
Extreme pH levels will produce denaturation The structure of the enzyme is changed The active site is distorted and the substrate
molecules will no longer fit in it At pH values slightly different from the enzyme’s
optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur
This change in ionisation will affect the binding of the substrate with the active site.
© 2007 Paul Billiet ODWS
The effect of pH
Optimum pH values
Enzyme activity Trypsin
Pepsin
pH
1 3 5 7 9 11
© 2007 Paul Billiet ODWS
Enzymes: Are most active at
optimum pH. Contain R groups of
amino acids with proper charges at optimum pH.
Lose activity in low or high pH as tertiary structure is disrupted.
pH and Enzyme Action
Optimum pH Values
Most enzymes of the body have an optimum pH of about 7.4.
In certain organs, enzymes operate at lower and higher optimum pH values.
ENZYME ACTIVATION BY INORGANIC IONS In the presence some inorganic ions some
enzymes show higher activity eg.Chloride ion activate salivary amylase,Ca. activates lipases.
Proenzymes in to enzymes. Coagulatio factors are seen in blood as
zymogen. Compliment cascade,these activities needed
occasionly.
Enzyme Inhibition
Competitive Inhibtion. Non-Competitive Inhibition. Un-competitive Inhibition. Suicide Inhibition. Allosteric Inhibition Key Enzymes Feedback Inhibition. Inducors.Glucokinase is induced by Insulin. Repression (Heme is reprossor of ALA Synthase.
Sigm
oidal Curve E
ffect
Sigmoidal curve
Exaggeration of sigmoidal curveyields a drastic zigzag line that shows the On/Off point clearly
Positive effector (ATP)brings sigmoidal curveback to hyperbolic
Negative effector (CTP)keeps
Consequently, Allosteric enzyme can sense the concentration of the environment and adjust its activity
Noncooperative(Hyperbolic)
Cooperative(Sigmoidal)
CTPATP
vo
vo
[Substrate]Off On
Juang RH (2004) BCbasics
EFFECT OF CONC.PRODUCT At Equilibrium as per law of mass action,the
reaction rate is slowed down,it can slow,stopped or reversed.
A—E1—B—E2—≠— C—E3—D.
Increase in conc. Of D will cause feed back Inhibition.
INDUCTION
Induction is effected through the process of derepression.
The inducer will relieve the repression on the operator site.
In the absence of glucose,the enzymes of Lactose metabolism will increase thousand times.
Insulin is Inducer of Hexokinase Enzyme. Barbiturates induce ALA Synthase.
REPRESSION
Inhibition and repression reduce the Enzyme Velocity.
In case of Inhibition the Inhibitor act directly on the Enzyme.
Repressor acts at the gene level,effect is noticed after a lag period of Hours or Days.
CO VALENT MODIFICATION Activity of Enzyme can be increased or
decreasd by co-valent modifications Eg.Either addition of group or Removal of group
Zymogen activation by partial proteolysis is an Eg. Of co-valent modification
ADP RIBOSYLATION
It is a type of co-valent modification. ADP-Ribose from NAD is added to enzyme/Protein. ADP Ribosylation of Alfa Sub unit of G Protein leads
to Inhibition of GTPase activity;hence G protein remains active.
Cholera toxin & Pertussive toxin act through ADP-Ribosylation.
ADP Ribosylation of Glyeraldehyde 3P-Dehydrosense,result in inhibition of glycolysis.
STABILIZATION
Enzyme molecules undergo usual wear & tear finally get degraded.Enzymes having thio (SH) groups eg Papian,Succinate dehydrogenase are stablized by glutathione. (G-SH).
Phosphofructokinase is stablized by growth hormone.
xRegulatory
subunit
o
Regulation of Enzyme Activity
o xS I
x oS
Sx
S
oS
AA
Po R xR
+
III
or
inhibitor
proteolysis
phosphorylation
cAMP orcalmodulin
or
regulatoreffector
P
(-)
(+)
Inhibitor Proteolysis
Phosophorylation
Signal transduction
Feedback regulation
Jua
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(2
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BC
ba
sics
REGULATION OF ENZYMES ‘’The action of enzymes can be
activated or inhibited so that the rate of enzyme productin responds to the physiologcal need of the cell done to achieve cellular economy’’
1. Allosteric Regulation. 2. Activation of Latent Enzyme. 3. Comprtmentation of Enzymes of different
Pathways.
4. Control of Enzyme Synthesis.
5. Enzyme Degradation.
REGULATION OF ENZYMES Control of metabolic pathway occour through
modification of Enzyme activity. One or more key enzyme on the pathway. Can be
involved in regulation. One enzyme that regulate is called rate limiting
enzyme or key enzyme of that path –way.Usually this is first enzyme.
This enzymes activity change in quantity of enzyme present orIntrinsic catalytic efficiency of enz. Molecule.
CHANGE IN ENZYME QUANTITY Absolute Quantity of Enz.is determined by balance
(Rate of Synthesis&Degradation) Enzyme whose synthesis is increased by inducer
are called inducible enz.Eg. Tryptophan pyrolase,Tyrosine Transaminase and HMG co-A Reductase.
Enz. Whose conc. Always maintained at particular level,independent of Inducor are called constitutive enz. Eg. Hexokinase.
Sometimes accumulation of metabolite inhibit its own synthesis.These are called repressor.
CHANGE IN CATALYTIC EFFICIENCY OF ENZYME Catalytic effeciency is regulated is modulated by A. Allosteric Regulation. B. Covalent modification. A. ALLOSTERIC REGULATION: Here the site is
different from substrate binding site, this site is called ALLOSTERIC SITE.
Low molecular wt. substances bind at site other than catalytic site,these are called ALLOSTERIC MODULATORS.Location is called allosteric site.
A.Activator A.Inhibitor. Allosteric Activator. Hexokinase: ADP Isocit.Dehydr. ADP Glu.Dehy. ADP Pyruvate Carboxylase Acetyl CoA
Allosteric Inhibitor. Glucose-6-P,ATP Glucose-6-P,ATP ATP, NADH.
ADP
HOMOTROPIC EFFECT: If the effector Substace is substrate itself it is called
homotropic effect. HETEROTROPIC EFFECT: Effector molecule is a
substance other than substrate. SECOND MESSENGER:Binding of many
hormones to their surface receptor induce a change in enzyme catalysed reaction by inducing the release of allosteric effector.These effector substances are called as 2nd messenger
Hormone is first messenger. Cont……
Examples of Second messengers are cAMP,cGMP and calcium etc.
These can change the enzyme conformation that may alter either Km or Vmax.
Based on this effect they are classified in to two classes.
1.K-class:Alter Km not Vmax. 2.V-class:Alter Vmax not Km.
CONFERMATIONAL CHANGES IN ALLOSTERIC ENZYMES.
Most of Enzymes are oligomeric, binding of effector moecule at the allosteric site brings a chage in the active site of enzyme leading to inhibition or activation.
Allosteric Enzyme exhist in two states. A. Tense (T) B. Relaxed (R ) Both are in equlibrium.
CCC
Allosteric Enzyme ATCase
+
Active relaxed form
Inactive tense form
ATCase
RR
RR
RR
CCC
COO-
CH2
HN-C-COO-
H H-
---
OH2N-C-O-PO3
2-
= OH2N-C-
=
COO-
CH2
N-C-COO-
H H
---
-
Catalytic subunits
Catalytic subunits
Regulatory subunits
ATP
CTP
Nucleic acidmetabolism
Feedback inhibition
AspartateCarbamoylphosphate
Carbamoyl aspartate
CTP
CTP
CTP
CTP
CTP
CTP
Juang RH (2004) BCbasics
Quaternary structure
EXAMPLE OF 2nd MESSENGER
GLYCOGEN BREAKDOWN.
GLYCOGEN SYNTHESIS.
SH2domain
The Reception and Transduction of Signals
G protein
GDP
+ Signal
-GDP+GTP
GDP
GTP
GTP
Adenylate cyclase
+ Signal
ActivationP
ProteinPhosphatase
GlycogenSynthase
GlycogenSynthase P
active
Insulin
P P
PP kinase
Glucagon
A
G-protein-linked Receptor
Enzyme-linked ReceptorThe third group: Ion-channel-linked Receptor
Gilman, Rodbell (1994)
Glycogen breakdown
Glycogen
Jua
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ba
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Sigm
oidal Curve E
ffect
Sigmoidal curve
Exaggeration of sigmoidal curveyields a drastic zigzag line that shows the On/Off point clearly
Positive effector (ATP)brings sigmoidal curveback to hyperbolic
Negative effector (CTP)keeps
Consequently, Allosteric enzyme can sense the concentration of the environment and adjust its activity
Noncooperative(Hyperbolic)
Cooperative(Sigmoidal)
CTPATP
vo
vo
[Substrate]Off On
Juang RH (2004) BCbasics
FEED BACK INHIBITION
Enzyme is inhibited by end product of reaction.
A-B-C-D-E-F……….P. P product will inhibit the enzyme which
converts A in to B.
COVALENT MODIFICATIONS Two well known processes A. PHOSPHORILATION. B. PARTIAL PROTEOLYSIS. A. Phosphorilation-dephosphorilation:many
enzymes are regulated by ATP dependent phosphorilation.Eg. Of Serine,Threonine,and tyrosine,catalysed by protein kinases.
cAMP Controls Activity of Protein Kinase A
R C
R C
R
RA
A
A
A
AA
A
A
C
C
Regulatorysubunits
Catalyticsubunits
cAMPActive kinase
C
CREB
CREB
P
Nucleus
Activation
Geneexpression
ONDNA
Alb
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s e
t a
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Mo
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PARTIAL PROTEOLYSIS
Some enzymes are secreted as inactive precursors called Proenzymes or Zymogens.
This convertion takes place as a selective proteolysis.
It is ir-reversible process Pepsinogen to pepsin Trypsinogen to trypsin.
MICHAELIS CONSTANT (Km) It is defined as the conc. Of the
substrate at which the reaction velocity is half of the maximum velocity.
Km is independent of enzyme conc. If an enzyme has a small value of Km, it
achieves maximal catalytic efficency at low substrate conc.
SIGNIFICANCE Glucokinase has high Km is low affinity for
glucose
Hexokinase have low KM High affinity for Glucose ie glucose will provide to the vital organs even at low glucose levels.
Lab. Significance: The sub. Conc. Kept at saturation point at least 10 times the Km so that reaction proceeds to completion.
Clinical Significance: The Km value for the given enzyme may differ from person to person and explains various response to drugs/chemicals.
INHIBITORS
Inhibitors Inhibitors are chemicals that reduce the rate of
enzymic reactions. The are usually specific and they work at low
concentrations. They block the enzyme but they do not usually
destroy it. Many drugs and poisons are inhibitors of enzymes
in the nervous system.
© 2007 Paul Billiet ODWS
The effect of enzyme inhibition Irreversible inhibitors: Combine with the
functional groups of the amino acids in the active site, irreversibly
Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase
© 2008 Paul Billiet ODWS
The effect of enzyme inhibition Reversible inhibitors: These can be
washed out of the solution of enzyme by dialysis.
There are two categories
© 2008 Paul Billiet ODWS
The effect of enzyme inhibition2. Non-competitive: These are not influenced by the
concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site
Examples Cyanide combines with the Iron in the enzymes
cytochrome oxidase Heavy metals, Ag or Hg, combine with –SH groups.
These can be removed by using a chelating agent such as EDTA
© 2008 Paul Billiet ODWS
Applications of inhibitors
Negative feedback: end point or end product inhibition
Poisons snake bite, plant alkaloids and nerve gases
Medicine antibiotics, sulphonamides, sedatives and stimulants
© 2008 Paul Billiet ODWS
Cell processes (e.g. respiration or photosynthesis) consist of series of pathways controlled by enzymes
A B C D E F
Enzyme pathways
eFeDeCeAeB
Each step is controlled by a different enzyme (eA, eB, eC etc)
This is possible because of enzyme specificity
© 2008 Paul Billiet ODWS
End point inhibition
The first step (controlled by eA) is often controlled by the end product (F)
Therefore negative feedback is possible
A B C D E F
The end products are controlling their own rate of production
There is no build up of intermediates (B, C, D and E)
eFeDeCeA eB
Inhibition
© 2008 Paul Billiet ODWS
ATP is the end point
This reaction lies near the beginning of the respiration pathway in cells
The end product of respiration is ATP If there is a lot of ATP in the cell this enzyme
is inhibited Respiration slows down and less ATP is
produced As ATP is used up the inhibition stops and
the reaction speeds up again
© 2008 Paul Billiet ODWS
The switch: Allosteric inhibition Allosteric means “other site”
E
Active site
Allosteric site
© 2008 Paul Billiet ODWS
Switching off
These enzymes have two receptor sites
One site fits the substrate like other enzymes
The other site fits an inhibitor molecule
Inhibitor fits into allosteric site
Substratecannot fit into the active site
Inhibitor molecule
© 2008 Paul Billiet ODWS
The allosteric site the enzyme “on-off” switch
E
Active site
Allosteric site emptySubstrate
fits into the active site
The inhibitor molecule is
absent
Conformational change
Inhibitor fits into allosteric
site
Substratecannot fit into the active site
Inhibitor molecule is present
E
© 2008 Paul Billiet ODWS
A change in shape
When the inhibitor is present it fits into its site and there is a conformational change in the enzyme molecule
The enzyme’s molecular shape changes The active site of the substrate changes The substrate cannot bind with the substrate
© 2008 Paul Billiet ODWS
Negative feedback is achieved The reaction slows down This is not competitive inhibition but it is
reversible When the inhibitor concentration diminishes
the enzyme’s conformation changes back to its active form
© 2008 Paul Billiet ODWS
Phosphofructokinase The respiration pathway accelerates and
ATP (the final product) builds up in the cell As the ATP increases, more and more ATP
fits into the allosteric site of the phosphofructokinase molecules
The enzyme’s conformation changes again and stops accepting substrate molecules in the active site
Respiration slows down
© 2008 Paul Billiet ODWS
Enzyme Inhibition (Mechanism)
I
I
S
S
S I
I
I II
S
Competitive Non-competitive Uncompetitive
EE
Different siteCompete for
active siteInhibitor
Substrate
Ca
rtoo
n G
uid
eEq
uatio
n an
d De
scrip
tion
[II] binds to free [E] only,and competes with [S];increasing [S] overcomesInhibition by [II].
[II] binds to free [E] or [ES] complex; Increasing [S] cannot overcome [II] inhibition.
[II] binds to [ES] complex only, increasing [S] favorsthe inhibition by [II].
E + S → ES → E + P + II↓EII
←
↑
E + S → ES → E + P + + II II↓ ↓EII + S →EIIS
←
↑ ↑
E + S → ES → E + P + II ↓ EIIS
←
↑
EI
S X
Juang RH (2004) BCbasics
Competitive Inhibition
Succinate Glutarate Malonate Oxalate
Succinate Dehydrogenase
Substrate Competitive InhibitorProduct
C-OO-
C-H C-H C-OO-
C-OO-
H-C-H H-C-H C-OO-
C-OO-
H-C-H H-C-H H-C-H C-OO-
C-OO-
C-OO-
C-OO-
H-C-H C-OO-
Km
Enzyme Inhibition (Plots)
I II Competitive Non-competitive Uncompetitive
Dir
ect
Plo
tsD
ou
ble
Rec
ipro
cal
Vmax Vmax
Km Km’ [S], mM
vo
[S], mM
vo
II II
Km [S], mM
Vmax
II
Km’
Vmax’Vmax’
Vmax unchangedKm increased
Vmax decreasedKm unchanged
Both Vmax & Km decreased
II
1/[S]1/Km
1/vo
1/ Vmax
II
Two parallellines
II
Intersect at X axis
1/vo
1/ Vmax
1/[S]1/Km 1/[S]1/Km
1/ Vmax
1/vo
Intersect at Y axis
= Km’
Juang RH (2004) BCbasics
The effect of enzyme inhibition Irreversible inhibitors: Combine
with the functional groups of the amino acids in the active site, irreversibly.
Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase.
© 2007 Paul Billiet ODWS
The effect of enzyme inhibition Reversible inhibitors: These can be
washed out of the solution of enzyme by dialysis.
There are two categories.
© 2007 Paul Billiet ODWS
The effect of enzyme inhibition1. Competitive:
These compete with the substrate molecules for the active site.
The inhibitor’s action is proportional to its concentration.
Resembles the substrate’s structure closely.
Enzyme inhibitor complex
Reversible
reaction
E + I EI
© 2007 Paul Billiet ODWS
CLINICAL APPLICATIONS OF COMPETITVE INHIBITORSDRUG ENZYME TRUE SUB. Clinical App.
ALLOPURINOL
XANTHINE OXIDASE
HYPOXANTHENE
GOUT
SULFONAMIDE
Dihydro pteroate Synthase
PABA ANTIBIOTIC
ETHANOL Al.Dehy. METHANOL METHANOL POISONING
The effect of enzyme inhibition2. Non-competitive: These are not influenced by
the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site.
Examples Cyanide combines with the Iron in the enzymes
cytochrome oxidase. Heavy metals, Ag or Hg, combine with –SH
groups.
These can be removed by using a chelating agent such as EDTA.
© 2007 Paul Billiet ODWS
Applications of inhibitors
Negative feedback: end point or end product inhibition
Poisons snake bite, plant alkaloids and nerve gases.
Medicine antibiotics, sulphonamides, sedatives and stimulants
© 2007 Paul Billiet ODWS
Enzyme Inhibitors Are Extensively Used
●● Sulfa drug (anti-inflammation)
Pseudo substrate Pseudo substrate competitive inhibitor
●● Protease inhibitorPlaques in brain contains protein inhibitor
● HIV protease is critical to life cycle of HIV
HIV proteaseHIV protease (homodimer):(homodimer):
↑inhibitor is used to treat AIDS Symmetry
Notsymmetry
→ Human aspartyl protease:(monodimer)
domain 1
Asp Asp
domain 2
subunit 2
Asp
subunit 1
Asp
Alzheimer's disease
DIAGNOSTIC SIGNIFICANCE ISOENZYMES: 1.CPK: MM,BB and MB.(Skeltol
muscles,Brain and Myocardium) 2. LDH:LDH-1 (H4) Myocardium LDH-2 (H3M) Erythrocytes. LDH-3 (H2M2) Brain. LDH-4 (HM3) Liver,Muscles. LDH-5 (M4) Liver, Muscles.
Plasma enzymes are of two types:Plasma enzymes are of two types:
1.1. A small group of enzymes secreted into A small group of enzymes secreted into the blood by certain cells e.g.the blood by certain cells e.g.the liver secretes zymogens (inactive the liver secretes zymogens (inactive form of enzymes) of blood coagulation.form of enzymes) of blood coagulation.
2.2. FUNCTIONAL: Lipoprotein FUNCTIONAL: Lipoprotein lipase,Pseudocholine estrase,blood lipase,Pseudocholine estrase,blood coagulation.coagulation.
3.3. NON FUNCTIONAL ENZYMES:NON FUNCTIONAL ENZYMES:
2. A large group of enzymes are released from cells during normal cell turnover.These enzymes function intracellularly (inside cells) and have no function in the blood.In healthy individuals, the blood levels of these enzymes are constant, as the rate of release from damaged cells into blood is equal to the rate of removal of enzymes from blood.
Elevated enzyme activity in blood Elevated enzyme activity in blood indicates tissue damage (due to indicates tissue damage (due to increased release of intracellular increased release of intracellular enzymes).enzymes).
A. Plasma Enzymes as diagnostic tools Diseases that cause tissue damage Diseases that cause tissue damage
result in increased release of result in increased release of intracellular enzymes into the intracellular enzymes into the plasma.plasma.
Determination of the level of these Determination of the level of these enzymes is used for diagnosis of enzymes is used for diagnosis of heart, liver, skeletal muscle, etc.heart, liver, skeletal muscle, etc.
The level of these enzymes in The level of these enzymes in plasma correlates with the extent of plasma correlates with the extent of tissue damage.tissue damage.
The presence of increased levels of The presence of increased levels of some enzymes in plasma is some enzymes in plasma is diagnostic to damage of a diagnostic to damage of a particular tissue; particular tissue; e.g. The enzyme alanine e.g. The enzyme alanine aminotransferase (ALT) is aminotransferase (ALT) is abundant in the liver and the abundant in the liver and the appearance of elevated levels of appearance of elevated levels of ALT in plasma indicates damage to ALT in plasma indicates damage to the liver.the liver.
Intracellular Distribution of Diagnostic Enzymes
LiverLiver HearHeartt
PancrePancreasas
SalivarSalivary y GlandsGlands
BonBonee
MusclMusclee
BiliarBiliary y TractTract
ProstaProstatete
LDLD55
ALTALTASTAST
LDLD11
ASTASTCKCK
LPSLPSAMSAMS
AMSAMS ALALPP
CKCK ALPALPGGTGGT
ACPACP
ISOENZYMES Isoenzymes or Isozymes are physically distinct
form of same enzyme having same specificity, but are present in different tissues of same organism, in different cell compartment.
Useful for diagnosing diseases of different organs.
Homomultimer:All the units are same. Heteromultimer:Sub units are different.These
are produced by different genes.
IDENTIFICATION OF ISOZYMES 1.Agar gel or PAGE.They have different mobility.
2.Heat stability. 3.Inhibitors.Isozymes may be sensative to different
inhibitors.eg.tartrate labile. 4. Km value or substrate specificity. Eg.Glucokinase
has high Km and Hexokinase has low Km for Glucose. 5.Co-Factors.Eg Mitochondrial isocitrate
dehydrogenase is NAD dependent,Cytoplasmic NADP dependent.
6.Localisation:H4 heart,M4 Muscles. 7.Specific antibodies identify sp.Isozyme.
Isoenzymes
Isoenzymes catalyze the same reaction in different tissues in the body.
Lactate dehydrogenase, which converts lactate to pyruvate, (LDH) consists of five isoenzymes.
Diagnostic Significance Enzymes The levels of diagnostic
enzymes determine the amount of damage in tissues.
B. Isoenzymes and Heart Diseases Isoenzymes (or isozymes) are a group of Isoenzymes (or isozymes) are a group of
enzymes that catalyze the same reaction.enzymes that catalyze the same reaction. However, these enzymes do not have the However, these enzymes do not have the
same physical properties (as they differ in same physical properties (as they differ in amino acid sequence).amino acid sequence).
Thus, they differ in electrophoretic Thus, they differ in electrophoretic mobility.mobility.
The plasma level of certain isozymes of The plasma level of certain isozymes of the enzyme Creatine kinase (CK) level is the enzyme Creatine kinase (CK) level is determined in the diagnosis of myocardial determined in the diagnosis of myocardial infarction.infarction.
DIAGNOSTIC IMPORTANCE Creatine
phosphokinase Alkaline phosphatase
CPK-BB,CPK-MM,CPK-MB
Alfa 1 ALP (liver) Alfa 2 ALP Heat labile
(Liver)& Heat stable (Placenta)
Prebeta ALP (Bones) Gama ALP (Colon) Regan ALP (Tumours)
DISORDERS DIAGNOSED BY ENZYMES1) Cardiac 1) Cardiac
Disorders.Disorders.
2) Hepatic 2) Hepatic Disorders.Disorders.
3) Skeletal Muscle 3) Skeletal Muscle Disorders. Disorders.
4) Bone Disorders.4) Bone Disorders.
5) Pancreatic 5) Pancreatic Disorders. Disorders.
6) Salivary gland 6) Salivary gland diseae (Mumps) diseae (Mumps)
7) Malignancies 7) Malignancies
CARDIAC MARKERS
CPK (MB) LDH (1) CARDIAC TROPONIN (I)&(T) BRAIN NATRIURETIC PEPTIDE (Marker of Ventricular function) AST ALT
LIVER MARKERS
ALT (Alanine amino transferase) ALP (Alkaline phosphatase) NTP (Nucleotide phosphatase) GGT (Gama glutamyl Tranferase)
PROSTATE MAR
PSA (prostate SP.ANTIGEN. ACP (Acid Phosphatase)
MUSCLE MARKER
CK (MM) AST (Aspartate Amino Transferase) ALD (Aldolase)
BONE MARKER
ALP (Alkaline Phosphatase)
1.Cardiac Markers:
e.g. Acute Myocardial Infarction (AMI).
1) The myocardium becomes ischemic and
undergoes necrosis.
2) Cellular contents are released into the
circulation. Blood levels of the following enzymes increase:
AST LD1 CK
2. Hepatic Disorders
a)a) Hepatocellular DisordersHepatocellular Disorders:: (1) Viral hepatitis: Hepatitis B & Hepatitis (1) Viral hepatitis: Hepatitis B & Hepatitis
C.C.
(2) Toxic hepatitis: caused by chemicals & (2) Toxic hepatitis: caused by chemicals & Toxins (e.g aflatoxin, Asp. flavus) Toxins (e.g aflatoxin, Asp. flavus)
Increased levels of the following Increased levels of the following enzymes :enzymes :ALTALT ASTAST LDLD55
b) b) Biliary tract disordersBiliary tract disorders::
The plasma levels of the following The plasma levels of the following
enzymes increase: enzymes increase:
ALPALP GGTGGT
3. Skeletal Muscle Disorders
Muscle dystrophy.Muscle dystrophy. Muscle trauma.Muscle trauma. Muscle hypoxia.Muscle hypoxia. Frequent I.M Injections.Frequent I.M Injections. The plasma levels of the following enzymes The plasma levels of the following enzymes
increase:increase:
CKCK ASTAST
4. Bone Disorders:
1)1) Paget’s Bone Disease: caused by Paget’s Bone Disease: caused by increased increased osteoclastic activity.osteoclastic activity.
2) Rickets2) Rickets
3) Osteomalacia:3) Osteomalacia: The plasma levels of the following The plasma levels of the following enzymeenzyme increase: increase:
ALPALP
5. Acute Pancreatitis
The plasma levels of the following The plasma levels of the following enzymes increase:enzymes increase:
LipaseLipase AMSAMS
6. Salivary Gland Inflammation: In Mumps:In Mumps:
The levels of The levels of -Amylase -Amylase (AMS)(AMS) is significantly is significantly increasedincreased
7. Malignancies
a)a) Plasma (Acid phosphatase) Plasma (Acid phosphatase) ACP ACP levels increase in: levels increase in:
• Prostatic carcinoma.Prostatic carcinoma.• Bone metastatic carcinoma Bone metastatic carcinoma
b) Plasma levels of Alkaline b) Plasma levels of Alkaline phosphatase (ALP) increase in: phosphatase (ALP) increase in:
• Pancreatic carcinoma.Pancreatic carcinoma.• Bile duct carcinoma.Bile duct carcinoma.• Liver metastasis.Liver metastasis.
c) Plasma levels of Total c) Plasma levels of Total Lactate Lactate dehydrogenase (LDH) dehydrogenase (LDH) increase in:increase in:
• LeukemiaLeukemia• Lymphomas.Lymphomas.• Liver metastasis.Liver metastasis.
B. Isoenzymes and Heart Diseases Isoenzymes (or isozymes) are a group of Isoenzymes (or isozymes) are a group of
enzymes that catalyze the same reaction.enzymes that catalyze the same reaction. However, these enzymes do not have the However, these enzymes do not have the
same physical properties (as they differ in same physical properties (as they differ in amino acid sequence).amino acid sequence).
Thus, they differ in electrophoretic Thus, they differ in electrophoretic mobility.mobility.
The plasma level of certain isozymes of The plasma level of certain isozymes of the enzyme Creatine kinase (CK) level is the enzyme Creatine kinase (CK) level is determined in the diagnosis of myocardial determined in the diagnosis of myocardial infarction.infarction.
Many isoenzymes contain different Many isoenzymes contain different subunits in various combinations.subunits in various combinations.
CK occurs in 3 isoenzymes, each is CK occurs in 3 isoenzymes, each is a dimer composed of 2 subunits (B a dimer composed of 2 subunits (B & M): CK1 = BB, CK2 = MB and & M): CK1 = BB, CK2 = MB and CK3 = MM, each CK isozyme shows CK3 = MM, each CK isozyme shows a characteristic electrophoretic a characteristic electrophoretic mobility.mobility.
Myocardial muscle is the only tissue Myocardial muscle is the only tissue that contains high level of CK2 (MB) that contains high level of CK2 (MB) isoenzyme.isoenzyme.
Appearance of CK2(MB) in plasma is Appearance of CK2(MB) in plasma is specific for heart infarction.specific for heart infarction.
Following an acute myocardial Following an acute myocardial infarction,CK2appears in plasma 4-8 infarction,CK2appears in plasma 4-8 hours following onset of chest pain hours following onset of chest pain (peak is reached after 24 hours).(peak is reached after 24 hours).
Alkaline Phosphatase
1.Alfa1-ALP Liver 2.Alfa2-ALP Liver (Heat Labile) 3.Pre Beta-ALP (BONES) 4.Gama ALP (Ulcerative Colitis) 5.Regan ALP (Bronchogenic cancer)
Sialic Acid Residues
ENZYMES IN OTHER BODY FLUIDS Adenosine deaminase in pleural
fluid :Elevated in Tuberculosis not in Malignant effusion.
LDH; In CSF,Pleural fluid & Ascitic Fluid. Elevated levels in Malignacy.
Enzymes as Therapeutic Agents Dissolving thrombus,Streptokinase,Urokinase.
Asparaginase used in some leukemias. Deoxyribonuclease is adminstered via respiratory route to
clear viscid secretions in pt. of cystic fibrosis. Serratiopeptidase is used to minimise edema in acute
inflamatory conditions. Hyaluronidase for hypovolumia Hemocoagulase used as hemostat. Fungal Diastase &Pepsin used as digestive enz. Ribozymes &Abzymes Streptodornase; DNA applied locally. Alpha-1-ant-trypsin; Emphysema.
ENZYMES USED FOR DIAGNOSIS Urease Urea. Uricase Uric Acid. Glucose Oxidase Glucose. Peroxidase Cholesterol. Hexokinase Glucose. Lipase Triglycerides. Alkaline phosphatase ELISA. Restriction endonuclease RFLP
Competitive Inhibition
Succinate Glutarate Malonate Oxalate
Succinate Dehydrogenase
Substrate Competitive InhibitorProduct
C-OO-
C-H C-H C-OO-
C-OO-
H-C-H H-C-H C-OO-
C-OO-
H-C-H H-C-H H-C-H C-OO-
C-OO-
C-OO-
C-OO-
H-C-H C-OO-
Enzyme Active Site Is Deeper than Ab Binding
Instead, active site on enzymealso recognizes substrate, butactually complementally fits the transition state and stabilized it.
Ag binding site on Ab binds to Agcomplementally, no further reactionoccurs.
X
cAMP Controls Activity of Protein Kinase A
R C
R C
R
RA
A
A
A
AA
A
A
C
C
Regulatorysubunits
Catalyticsubunits
cAMPActive kinase
C
CREB
CREB
P
Nucleus
Activation
Geneexpression
ONDNA
Alb
ert
s e
t a
l (2
00
2)
Mo
lecu
lar
Bio
log
y o
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ell
(4e
) p
. 8
57
, 8
58
HIV protease vs Aspartyl protease
Asymmetric monomer
↓ HIV protease HIV protease (homodimer)
HIV Protease inhibitor is used in treating AIDS
Symmetricdimer
Asp
subunit 2
↑Aspartyl protease (monomer)
subunit 1
Asp
domain 1 domain 2
Asp Asp
Juang RH (2004) BCbasics
Enzyme Inhibitors Are Extensively Used
●● Sulfa drug (anti-inflammation)
Pseudo substrate Pseudo substrate competitive inhibitor
●● Protease inhibitorPlaques in brain contains protein inhibitor
● HIV protease is critical to life cycle of HIV
HIV proteaseHIV protease (homodimer):(homodimer):
↑inhibitor is used to treat AIDS Symmetry
Notsymmetry
→ Human aspartyl protease:(monodimer)
domain 1
Asp Asp
domain 2
subunit 2
Asp
subunit 1
Asp
Alzheimer's disease
Sulfa Drug Is Competitive Inhibitor
-COOHH2N-
-SONH2H2N-
PrecursorFolicacid
Tetrahydro-folic acid
SulfanilamideSulfa drug (anti-inflammation)
Para-aminobenzoic acid (PABA)
Bacteria needs PABA for the biosynthesis of folic acid
Sulfa drugs has similar structure with PABA, andinhibit bacteria growth.
Domagk (1939)
SH2domain
The Reception and Transduction of Signals
G protein
GDP
+ Signal
-GDP+GTP
GDP
GTP
GTP
Adenylate cyclase
+ Signal
ActivationP
ProteinPhosphatase
GlycogenSynthase
GlycogenSynthase P
active
Insulin
P P
PP kinase
Glucagon
A
G-protein-linked Receptor
Enzyme-linked ReceptorThe third group: Ion-channel-linked Receptor
Gilman, Rodbell (1994)
Glycogen breakdown
Glycogen
Jua
ng
RH
(2
00
7)
BC
ba
sics
Signal Transduction Network (Ras vs. P53)
Cytosol
Cell membrane
Ras
Effectorenzyme
Signal protein
E2F Transcriptionfactor Target gene
mRNA
Inhibitor
P53
Cell division ON
Signal
Receptor
Nucleus
Ribosome
Transcription
Transcription
Apoptosis
Cell function are controlled by protein interactions
mRNA
Regulator protein
Juang RH (2007) BCbasics
SH2domain
The Reception and Transduction of Signals
G protein
GDP
+ Signal
-GDP+GTP
GDP
GTP
GTP
Adenylate cyclase
+ Signal
ActivationP
ProteinPhosphatase
GlycogenSynthase
GlycogenSynthase P
active
Insulin
P P
PP kinase
Glucagon
A
G-protein-linked Receptor
Enzyme-linked ReceptorThe third group: Ion-channel-linked Receptor
Gilman, Rodbell (1994)
Glycogen breakdown
Glycogen
Jua
ng
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(2
00
7)
BC
ba
sics
P
P
A
GP kinase
GP kinase
GP a
GP b
Glycogen synthase
Glycogen synthase P
Protein phosphatase-1
Protein phosphatase-1
Protein phosphatase inhibitor-1
Protein phosphatase inhibitor-1
Glycogen
PKA
P
active
inactive
PhosphataseG
luca
gon
Classification of Proteases
MetalProtease
SerineProtease
CysteineProtease
AspartylProtease
Carboxy-peptidase A
ChymotrypsinTrypsin
Papain
PepsinRenin
H57H57
D102D102
S195-OS195-O--
C25-SC25-S--
H195H195
D215D215
D32D32H2O
Non-specific
Non-specific
AromaticBasic
Non-polar
EDTAEGTA
DFPTLCKTPCK
PCMBLeupeptin
Pepstatin
Family Example Mechanism Specificity Inhibitor
E72E72 H69H69
Zn2+
H196H196
Juang RH (2004) BCbasics
Modification of Subtilisin and Its Activity Change
No enzyme 1
Asn155 → Leu ● ● ● 10,000,000
(Asn155 stabilizes transition state)
His & Asp → Ala ● ○ ○ 37,000Ser, His & Asp → Ala ○ ○ ○ 4,000Subtilisin ● ● ● 10,000,000,000
Active Site RelativeModification Triad: Ser His Asp activity
Ser → Ala ○ ● ● 5,000Asp → Ala ● ● ○ 330,000
Serine Protease and AchEChymotrypsin – Gly – Asp – Ser – Gly – Gly – Pro – Leu – Trypsin – Gly – Asp – Ser – Gly – Gly – Pro – Val – Elastase – Gly – Asp – Ser – Gly – Gly – Pro – Leu –Thrombin – Gly – Asp – Ser – Gly – Gly – Pro – Phe –Plasmin – Gly – Asp – Ser – Gly – Gly – Pro – Leu –Acetylcholinesterase – Gly – Glu – Ser – Ala – Gly – Gly – Ala –
Chymotrypsin – Val – Thr – Ala – Ala – His – Cys – Gly – Trypsin – Val – Ser – Ala – Gly – His – Cys – Tyr – Elastase – Leu – Thr – Ala – Ala – His – Cys – Ile – Thrombin – Leu – Thr – Ala – Ala – His – Cys – Leu – Plasmin – Leu – Thr – Ala – Ala – His – Cys – Leu – Acetylcholinesterase – – – – – – – – – – – – – His – – – – – – – –
Ser
19
5
Chymotrypsin – Thr – Ile – Asn – Asn – Asp – Ile – Thr –Trypsin – Tyr – Leu – Asn – Asn – Asp – Ile – Met – Elastase – Ser – Lys – Gly – Asn – Asp – Ile – Ala – Thrombin – Asn – Leu – Asp – Arg – Asp – Ile – Ala – Plasmin – Phe – Thr – Arg – Lys – Asp – Ile – Ala – Acetylcholinesterase – – – – – – – – – – – – – – Asp – – – – – – –
His
57
Asp
102
Adapted from Dressler & Potter (1991) Discovering Enzymes, p.244
H
AchE
AchE Has Similar Catalytic Mechanism
O -
C
H
O CH3
CH3–C–O–CH2–CH2–N–CH3
CH3
+
H-O-H
AchE
O
C
H
OCH3–C
CH3
HO–CH2–CH2–N–CH3
CH3
+
H2O
AchE
O -
C
H H
O CH3–C–OH
Adapted from Dressler & Potter (1991) Discovering Enzymes, p.243
AchE
O -
C
H
OCH3–C
CH3
O–CH2–CH2–N–CH3
H CH3
+
↓Deacylation
Acylation↑
Different Enzymes Might Adopt Same Mechanism
O -
C
Sesame Triad
Hi, Everybody!Hi, Everybody!
← Useful
↙ Amusing
Juang RH (2004) BCbasics
Divergent evolution
Asp--His--Ser
Asp--His--Ser
Convergent evolution
Convergent and Divergent
TrypsinChymotrypsin Elastase Thrombin Plasmin
AcetylcholinAcetylcholinesteraseesteraseAcetylcholinAcetylcholinesteraseesterase
ThyroglobulinThyroglobulinThyroglobulinThyroglobulin
C NC
C
H
O
CC
CO
O
Ester bond
Peptide bond
EvolutionEvolutionMolecularMolecular
hydrolyzeacetylcholine
Serine Protease
Juang RH (2004) BCbasics
Activity Regulation of Glycogen Phosphorylase
PA
PA
P
P
A
A
Covalent modificationCovalent modification
P
P
GP kinase
GP phosphatase 1
No
n-co
valent
No
n-co
valent
PA
PA
P
PPA
PAA
A
A
AMP
ATPGlc-6-PGlucoseCaffeine
GlucoseCaffeine
spontaneously
R
T
R
T
Ga
rre
tt &
Gris
ha
m (
19
99
) B
ioch
em
istr
y (2
e)
p.6
79
CCC
Allosteric Enzyme ATCase
+
Active relaxed form
Inactive tense form
ATCase
RR
RR
RR
CCC
COO-
CH2
HN-C-COO-
H H-
---
OH2N-C-O-PO3
2-
= OH2N-C-
=
COO-
CH2
N-C-COO-
H H
---
-
Catalytic subunits
Catalytic subunits
Regulatory subunits
ATP
CTP
Nucleic acidmetabolism
Feedback inhibition
AspartateCarbamoylphosphate
Carbamoyl aspartate
CTP
CTP
CTP
CTP
CTP
CTP
Juang RH (2004) BCbasics
Quaternary structure
xRegulatory
subunit
o
Regulation of Enzyme Activity
o xS I
x oS
Sx
S
oS
AA
Po R xR
+
III
or
inhibitor
proteolysis
phosphorylation
cAMP orcalmodulin
or
regulatoreffector
P
(-)
(+)
Inhibitor Proteolysis
Phosophorylation
Signal transduction
Feedback regulation
Jua
ng
RH
(2
00
4)
BC
ba
sics