Regulation of Enzyme Activity

Outline the regulation of enzyme activity (10 minutes)

Sub cellular compartmentalization

-Enzyme located in specific cellular organelles (eg mitochondria)

-each organelles surround by membrane with unique permeability properties

-these membrane regulate entry or exit of substrate/product

Induction of enzyme synthesis

-Some enzyme are synthesized only when substrate is available

-thus, enzyme activity are regulated by substrate

Zymogen activation

-Enzyme is secreted as larger inactive proenzyme

-zymogen is activated by specific mechanism that cleaves larger inactive enzyme to active enzyme

examples

trypsinogen to trypsin

pepsinogen to pepsin

Product inhibition

-Higher concentration of substrate binds to enzyme and inactivate it

-for example, inhibition of hexokinase by glucose 6 phosphate

-mainly for enzyme that catalyze unidirectional reaction

Feedback inhibition

-inhibition of first enzyme in a sequence of metabolic reaction by the product of last enzyme

-eg regulation of cholesterol synthesize by cholesterol through feedback inhibition of enzyme HMG coA reductase

Covalent modification

-Regulation of metabolism according to physiological need

-phosphorylation/dephosphorylation of enzyme by cAMP mediated mechanism

eg : phosphorylation of glycogen phosphorylase activate it

phosphorylation of glycogen synthase inactivate it

Allosteric regulation

-other site than active site

-regulated by allosteric activator and inhibitor