human diseases of carbohydrate metabolism inherited enzyme deficiencies mutations that change enzyme...

Human diseases of carbohydrate metabolism

Inherited enzyme deficiencies

Mutations that change enzyme function or abolish enzyme activity

Most are recessive since only one functional copy of gene is sufficient for needed activity

Diabetes

Lactose intolerance

Galactosemia

Glycogen storage disease

Monosaccharides - Monosaccharides - AldosesAldoses

# Isomers = 2n wheren = # of chiral carbons

Epimers – differ in configuration at only one chiral carbon

Enantiomer

Distant chiral CFrom most oxidized

Not all made in nature

Monosaccharides - Monosaccharides - KetosesKetoses

# Isomers = 2n wheren = # of chiral carbons

Cyclization - aldohexoseCyclization - aldohexose

Draw most oxidized carbon (C1 aldose and C2 ketose) on right and number C clockwise

In ring most oxidizes carbon new chiral center (anomeric C)

Transfer information from Fisher projections-OH on right then down in Haworth-OH on left then up in HaworthBulky substituent on highest numbered

carbon points up

rapid equilibrium Anomers

Hemiacetal

Cyclization - aldopentoseCyclization - aldopentose

Haworthprojection

Anomers

Equilibrium

Anomeric C

Glycolysis: Steps 2 and 3Glycolysis: Steps 2 and 3

Stereospecific: uses -Glc; produces 100% -D-fructose-6-phosphate

Opens the chainduring the rxn

PFK-1

utilizes 100% -anomer

36% -fructose 64% -fructose

CH2OH

OH

Glycoside Bonds – DisaccharidesGlycoside Bonds – Disaccharides

Hemiacetals -a reactive carbonyl that can be oxidized.

reducingnon-reducing

non-reducing sugar

No open chain equil

anomer: refers to free C1 OH

Glycoside Bonds – Glycoside Bonds – DisaccharidesDisaccharides

epimer

Most abundant disacc. in nature (plants)

Amylose

Polysaccharides – Structure

Humans don’t have -glucosidases

Microbe that live in ruminants do

Plant cell walls, stems and branches

300- 15,000 Glc residues

180 deg rotation

termites

Rigid extended conformationH-bondingForms bundles or fibrils

Cellulose -(1-4) linkage

Polysaccharides – Glucose Storage

Amylose

Amylopectinand

Glycogen

• Plant starch – mixture of amylose and amylopectin

• Animals glycogen

No template (ie no gene)

Homoglycans- one type of monosaccharide

100-1000 glucose residues (maltose units)

Amylopectin:branch every 25 residues

Glycogen:branch every 8-12 residues

10% mass of liver

Polysaccharides -Polysaccharides -Starch DegradationStarch Degradation

• Humans digest starch via two enzymes:– α -amylase -

endoglycosidase of α-(1-4) linkages (random)

– debranching enzyme(cleaves limit

dextrans)

• Higher plants have– β- amylase exoglycosidase

of α- (1-4) linkages, releasing the disaccharide maltose Single reducing end

Know how starch is broken down !

multiple non-reducing end

Glycogen MetabolismGlycogen Metabolism

Synthesis: Different enzymes for syn and degradation

Driven by PPi hydrolysis

Major regulatory step

Amylo-(1,4 1,6)-transglycolase catalyzes the branch point. (Alpha 1-6 link)

(hormonally regulated)

Pre-existingGlycogenin primer

Key regulationby phosphorylation

Degradation:

Phosphorolysis rxn. Generates phosph-sugar not free glc

Two subunits, two catalytic sites, allosteric sites. AMP- activator; ATP & Glc-6-P – inhibitor.

Phosphorylation: active (phosphorylase a).Dephosphorylated: less active (phosphorylase b).

Primary regulation

Reg by ATP and G-6-P

Primarily by phosphorylation

phosphorolytic

Consequences of branch

Branching inc speed ofsyn and degradation

Sequential removal of GlcFrom non-reducing end

Stops 4 Glc from branch pt

Energy yield from glycogenHigher than from glc

Reducing vs non-reducing ends

solubility

Rate of syn/degradation





Diabetes

Lactose intolerance

Galactosemia


α -amylase

lactase Glc + Gal

Glc-6-P

In liver

Absorbed from intestine

Major source of energy for nursing animals

20% of caloric intake of infants

Glucose metabolism

Glc 6-P

Glc

Fruc 6-P

Fruc 1,6-P

Glc Glc 1-P glucogen

glucogen

lactase Glc + Gal

Glc-6-P

In liver

Absorbed from intestine

Major source of energy for nursing animals

20% of caloric intake of infants

X

XTwo inherited metabolic errors

Hypolactasia (lactose intolerance)

Galactosemia

Lactose Intolerance

Single gene defect

X

Normal decrease in enzyme by 6 yrs old10% of original activity

(Northern Europeans are lactase producing adults)

Lactase deficient people:

Bloated/ gas and diarrhea

Can also hinder absorption of other nutrients

bacteria in colon ferment to lactic acid, methane and H gasLactose passes intact into colon

Mutation in chromosome 2

Avoid dietary lactoseTake enzyme substitute

cataracts

X

Galactosemia

Galactose 1-P accumulates in liver cells (high galactose in blood and urine)

Decrease liver function and cataracts death

CNS damage and mental retardation (even if avoid milk)

Cataracts (clouding) due to high galactose in eye. Converted to galactol allowingdiffusion of water into eye

Glucose metabolism

Glc 6-P

Glc

Fruc 6-P

Fruc 1,6-P


glucogen

Glycolysis and CancerGlycolysis and Cancer

Net Reaction:Glucose + 2 ADP + 2 NAD+ + 2 Pi 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

Defined: Glucose is converted anaerobically to the three carbon acid pyruvate

Oxidative phosphorylation: allows more energy extracted from Glc

Generates ATP at higher rate than Oxid Phosp

Aerobic glycolysis: Warburg effect

Otto Warburg-cancer cells utilize glycolysis even in presence of O2

Max energy when pyruvate from glycolysis enters Citric Acid Cycle

Initial stages of tumor growth vessels grow at slower rate: cells deprived of O2

Cells switch to reliance to glycolysis

Glycolysis and CancerGlycolysis and Cancer

Can visualize tumors based on inc sugar uptake (PET scan)

Continue to rely of Glycolysis even when O2 restored to tumor

Treatment?? Blocking lactose dehydrogenase (block NAD regeneration turn off Glycolysis)

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Fructose-1,6-bisphosphate

Dihydroxyacetone phosphate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Glyceraldehyde-3-phosphate

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

Hexokinase

Glucose-6-phosphate isomerase

Phosphofructokinase-1

Trios phosphate isomerase

Aldolase

Glyceraldehyde-3-phosphate dehydrogenase

Phosphoglycerate kinase

Phosphoglycerate mutase

Enolase

Pyruvate kinase

ATP

ADP

ATP

ADP

ADP

ATPADP

ATP

ADP

ATPADP

ATP

NADH + H+

NAD+ + Pi

NADH + H+

NAD+ + Pi

H2O H2O

Phosphorylation

Phosphorylation

Substrate Level Phosphorylation

Substrate Level Phosphorylation

Oxidation and Phosphorylation

Isomerization

Cleavage

Isomerization

Rearrangement

Dehydration

Know key reg steps!

Enzymatic Regulation of GlycolysisEnzymatic Regulation of Glycolysis

CAC intermediates, slow down, there is already adequatesupply of energy

Not moving forward, stop converting ATP

Cellular rxns are converting ATP and ADP, make more ATP

You’ve committed!Bi-phosphated furanoses, keep pathway moving

Glycolysis: Hexokinase IsozymesGlycolysis: Hexokinase Isozymes

Can’t leave the cell with negative charge

I-III IV

Isozymes Different inhibition profiles Location, Km Control point

Hexokinases (I-III)-regulated negatively by Glc-6-P-if later steps slow down, Glc-6P builds up

Glucokinase (IV) in Liver-regulated negatively by Fru-6-P-pulls glucose out of bloodstream until equil-liver can produce more Glc-6-P-converts Glucose to Glycogen storage

Glc 6-P

Glc

Fruc 6-P

Fruc 1,6-P


Insulin Dependent UptakeMuscleAdipose

Hormones InvolvedHigh blood [Glc], insulin releasedLow blood [Glc], glucagon released

in Liver

Major function of liver: maintain constant level of Glc in bloodRelease Glc (from glycogen) during muscle activity and between meals

Most cases Glc-6-P is end product---used in other pathways - glycogen, starch, pentose, hexose synthesis

Enzyme only found in liver, kidney, small intestines

Bound to ER with active site towards lumen

Hydrolysis of phosphate irreversibly forms glucose

Secretory pathway exports to blood stream for other tissues

Glucose 6-phosphataseGlucose 6-phosphatase

Lactate- produced in RBC and Muscle

Cori cycle

Lactate to pyruvate in liver

Body does not transfer pyruvate

Major function of liver: maintain constant level of Glc in blood

Release Glc during muscle activity and between meals

Breakdown of glycogen to Glc 6-P (does not leave the cell)

Liver contains glc 6-phoshatase enzyme

Glc not major fuel in liver

Regulation of Phosphofructokinase-1Regulation of Phosphofructokinase-1

Citrate - feedback inhibitor - regulates supply of pyruvate - links Glycolysis and CAC

Fru-2,6-bisphosphate - strong activator - produced by PFK-2 when excess fru-6-phosphate - indirect means of substrate stimulation or feed forward activation

ATP - product of pathway - allosteric inhibitor

AMP - allosteric activator - relieves inhibition by ATP

Large oligomeric enzyme bacteria/mammals - tetramer yeast - octamer

Regulation of Pyruvate KinaseRegulation of Pyruvate Kinase

High blood [Glc]

Allosteric (feed-forward) activation Fructose-1,6-bisphosphate -allosterically activates -produced in step three -links control steps together

+ F 1,6 BP

Inactivation by covalent modification -blood [Glc] drops, glucagon released -liver protein kinase A (PKA) turned on -PKA phosphorylates pyruvate kinase

Allosteric inhibition by ATP -product of pathway and CAC

Low blood [Glc]

Regulation of Glycogen MetabolismRegulation of Glycogen MetabolismHormonal Regulation:

Via cAMP

Via PIP3

Fed statefasting

Insulin: secreted by pancreas when Glc high inc rate of transport into cell and glycogen syn

Glucagon: secreted when Glc low

Epi: released by adrenal gland in response to neural signal (flight or flight)

Sudden energy response

GLUT4

glycogen PPP

Glc also syn from pyruvate (lactate and amino acids) Liver/kidney

Glc needed in brain/muscle

Gluconeogenesis Gluconeogenesis

Liver

- 3 places differ- control points in glycolysis - 4 new enzymes

ATP energy, NADH reducing equivalents consumed

Gluconeogenesis: Regulation: Regulation

Low [Glc]: glucagon increases protein kinase A (activates Fru-2,6-bisP phosphatase) lowering [Fru-2,6-bisP].

Activate Glc synand

Loss of glycolysis stim

Modulate one enzyme and affect 2 opposing pathways

Sensitive regulatory point

Regulation of Glycogen MetabolismRegulation of Glycogen MetabolismHormonal Regulation:

Via cAMP

Via PIP3

Fed statefasting

Insulin: secreted by pancreas when Glc high inc rate of transport into cell and glycogen syn

Glucagon: secreted when Glc low

Epi: released by adrenal gland in response to neural signal (flight or flight)

Sudden energy response

GLUT4

Intracellular Regulation of Glycogen Metabolism by Interconvertible Enzymes:

Low [Glc]Simultaneouseffect

Low glc activate kinase and breakdown

High [Glc]





Diabetes

Lactose intolerance

Galactosemia

Glycogen storage diseaseUnderstand how enzyme deficiency leads to accumulation of glycogen

Other symptoms

Treatment, if any


Glc 6-P

Glc

Fruc 6-P

Fruc 1,6-P


glucogen

X

X XX

IIV

V

VII

II, III, VI

I Glucose-6-Phosphatase in liver (von Gierk’s disease):Liver enlargementhypoglycemia (low blood glc) when fasting

Branching enzyme in organs (liver) (Andersen’t disease)Liver dysfunction and early death

Glycogen phosphorylase in muscle (McArdle’s disease)

Phosphofructokinase in muscleVII

IV

V

Inability to exercise

Muscle cramps with exercise

All defects lead to glycogen accumulation

Glycogen accumulation and


Glucose-6-Phosphatase deficiency in liver (von Gierk’s disease):Glc not released into blood

hypoglycemia (low blood glc) between meals infant in convulsions

Type I:

No response to Epinephrine or Glucagon

Large amounts of glycogen in liver (G-6-P inhibits breakdown)

Glc-6-P increases glycolysis inc lactate/pyruvate in blood (Lactic acidosis)

Continuous feedings of cornstarch (intragastric feeding)

Drug induced inhibition of Glc uptake by liver Surgical transplant of portal vein (normally intestine-liver)

Glc to peripheral tissues before liver

Liver enlargement

Delayed puberty, short stature


Type IV:

Branching enzyme deficiency in organs (liver) (Andersen’s disease)

Accumulate abnormal glycogen

Failure to thrive----- death 2-5 yrs old

Liver dysfunction

Reduced solubility of glycogen

Foreign body immune response??

Most severe disease


Type V:

Glycogen phosphorylase deficiency in muscle (McArdle’s disease)

No breakdown of glycogen

Exercise indices muscle cramps otherwise normalEffective utilization of muscle glycogen not essential to life

Can’t provide fuel for glycolysis to keep upDemand for ATP

Muscle cramps correlate with inc ADP

Vasodialation-muscle now has access to Glcand fatty acids in blood

NMR on forearm muscle

human diseases of carbohydrate metabolism inherited enzyme deficiencies mutations that change enzyme...

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