Regulation Of Enzyme

Renu Maurya

8 years ago

Regulation Of Enzyme

REGULATION OF ENZYMES

Mechanism for regulating the enzyme activity-

Allosteric modulation
Covalent modification
Induction and repression of enzyme synthesis

Allosteric modulation-

Allosteric Enzymes have a catalytic site where the substrate binds and a separate site where a modifier binds.
Examples-

Enzyme	Pathway	Stimulator	Inhibitor
Phosphofructokinase	Glycolysis	Fructose-2,6- iphosphate	Citrate
Isocitrate dehydrogenase	TCA
Carbamoyl Phosphate Synthetase I			N Acetyl Glutamate (NAG)
Acetyl CoA Carboxylase	Fatty acid synthesis	Citrate	Acyl CoA

Covalent Modification-

The most common covalent modification is the addition or removal of a phosphate group.
Two types-

Irreversible- partial proteolysis/ zymogen activation
Reversible- addition/ removal of a particular group.

Methods of Reversible covalent modifications-

Phosphorylation/ dephosphorylation (most common)
Methylation
Adenylation
ADP reibosylation
Acetylation

Enzyme	Active	Inactive
Glycogen Synthase	Dephosphorylated	Phosphorylated
Pyruvate dehydrogenase	Dephosphorylated	Phosphorylated
HMG- CoA- reductase	Dephosphorylated	Phosphorylated
HMG- Co reductase kinase	Phosphorylated	Dephosphorylated

Protein kinase mostly add phosphoryl group to a serine, threonine or tyrosine.
Specific activity– number of enzyme units per milligram of protein.
Catalase has the highest turnover number and hence is the fastest active enzyme.

Exam Question

Allosteric modulation example-

Enzyme	Pathway	Stimulator	Inhibitor
Phosphofructokinase	Glycolysis	Fructose-2,6- biphosphate	Citrate

The most common covalent modification is the addition or removal of a phosphate group.
Irreversible covalent modification- partial proteolysis/ zymogen activation
Methods of Reversible covalent modifications-

a. Phosphorylation/ dephosphorylation (most common)

Enzyme	Active	Inactive
Glycogen Synthase	Dephosphorylated	Phosphorylated
Pyruvate dehydrogenase	Dephosphorylated	Phosphorylated
HMG- CoA- reductase	Dephosphorylated	Phosphorylated
HMG- Co reductase kinase	Phosphorylated	Dephosphorylated

Protein kinase mostly add phosphoryl group to a serine, threonine or tyrosine.
Specific activity- number of enzyme units per milligram of protein.
Catalase has the highest turnover number and hence is the fastest active enzyme.

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