enzymes o -co -c hi, everybody! objectives enzymes as biological catalysts the properties of enzymes...
TRANSCRIPT
EnzymesO -
C
Hi, Everybody!Hi, Everybody!
Objectives Objectives
Enzymes as Biological Catalysts
The Properties of Enzymes
Enzyme classification
Substrate Binding and
Enzyme Action
Enzyme Inhibition
Regulation of enzyme activity.
Applications of Enzyme Action
Intended learning outcomes(ILO)
Intended learning outcomes(ILO)
State the different properties of enzymes.
2-PROPERTIES OF ENZYMES
2-PROPERTIES OF ENZYMES
Enzymes properties1-All enzymes are proteins
2-Enzymes do not determine the direction of reaction
3- Enzymes are highly specific
4-Some enzymes require cofactors
• Ribozymes= Small group of catalytic RNA molecule which share in the posttranscriptional modification of nascent RNA.
Pre-mRNA Mature mRNA
Ribozyme
Cleave phosphodiester bond of RNA
1-All enzymes are proteins except ribozymes
2-Enzymes do not determine the direction of reaction
They only accelerate reaching the equilibrium
state.
The direction of the reaction is determined by the free energy change of
the reaction=ΔG
From reactants to products
OrFrom products to
reactants
3 -Enzymes are highly specific
TO their Substrate
To the reaction
3-Enzymes are the most specific catalyst
Enzyme specificity
• The enzyme is specific for one substrate e.g.
• glucokinase act only on glucose but not other hexoses.
• Urease acts on urea.Absolute
specificity
• Enzymes Catalyze the same type of reaction on a number of structurally related substrates having the same type of bond.
• Hexokinase act on glucose, fructose, mannose
• Peptidase acts on peptide bonds in different proteins.
Relative specificity
Enzyme specificity
• The enzyme is directing not only to the type of bond but also to the site of bond and the groups around it .
• Chemotrypsin acts on peptide bonds formed by certain amino acids
Group specificity
• The enzyme are specific to the D- or to the L- isomer but not both.
• e.g. L-amino acid oxidase for L-amino acids not for D-AA.
Stereospecificity
Enzyme specificity
Specificity of Ser-Protease Family
COO-
CAsp
COO-
CAsp
Active Site
Trypsin Chymotrypsin Elastasecut at Lys, Arg cut at Trp, Phe, Tyr cut at Ala, Gly
Non-polarpocket
Dee
p an
d ne
gativ
ely
char
ged
pock
et Shallow andnon-polar
O O–C–N–C–C–N –
C C C C NH3+
O O–C–N–C–C–N –
C
O O–C–N–C–C–N –
CH3
Jua
ng
RH
(2
00
4)
BC
ba
sics
Some enzymes require a cofactor
Let’s meetthe team…
Cofactors
Metal ions)Mg, Fe, Cu(
Coenzymes non protein, low molecular weight
Usually derived from vitamins, heat stable
Bind loosely with enzymeFew bind firmly(prothestic group)
Regenerated after reaction
NON protein part
coenzymes Metal ion
NON protein part
coenzymes Metal ion
Metalloenzyme(tightly bound)
Glutathione peroxidase contain
Se
Metal activated enzymes(loosely
bound)Coagulation enzymes
require Ca in blood
NON protein part
coenzymes
Tightly bound(Prosthetic group)
Loosely bound, e.g. NAD
Cofactors(metal)
NON protein part
coenzymes
Tightly bound(Prosthetic group)
Covalently bound
e.g. biotin, heme
Non covalently bound
e.g. FMN
Loosely bound, e.g.
NAD
Cofactors(metal)
NON protein part
coenzymes
Tightly bound(Prosthetic group)
Covalently bound
e.g. biotin, heme
Non covalently
bounde.g. FMN
Loosely bound,
e.g. NAD
Cofactors(metal)
Metalloenzyme(tightly boundGlutathione peroxidase contain Se
Metal activated enzymes(loosely
bound)Coagulation
enzymes require Ca in blood
Apoenzymes, coenzymes holoenzymes
Let’s meetthe team…
Apoenzyme (protein part )
Coenzymes(non protein part)
Holoenzyme
)active catalytic unit(
Some enzymes require cofactors
Are specific non-protein organic or metallo-organic heat stable low molecular weight compounds required for the activity of the enzyme:
Co-enzymes
Co-enzymes acts asTransient carrier of
specific functional groups or atoms
•NAD carries the hydride ion during oxidation reduction reaction.
Co-substrate(second substrate)
•Coenzymes has affinity for the enzyme similar to that of the substrate.
•The chemical changes in the coenzymes counterbalance those occurring in the substrate.
•If the substrate is oxidized, the coenzyme is reduced
• The changes occurring in the coenzyme may more important than that occurring in the substrate.
• The reaction catalyzed by lactate dehydrogenase is mainly for oxidation of NADHH rather than reduction of pyruvate to lactate
Co-enzymes
Vitamin Co-enzyme Function
Thiamine ( B1) TPP Oxidative decarboxylation
Riboflavin (B2) FAD,FMN
Dehydrogenation
Lipoic acid Lipoic acid Oxidative decarboxylation
Niacine NAD,NADP
Dehydrogenation
Pyrodoxine PLP Amino acid metabolism
Biotin Biotin carboxylation reaction
Pantothenic Acid
CoA SH 1.Carobydrates,fat and lipids metabolism
Folic Acid THF One carbon unit metabolism
Co-enzymes derived from vitamins