ENZYME INHIBITION

• Enzyme inhibitor binds with enzyme and decreases a catalytic activity.
• Types of Enzyme Inhibition-

1. Reversible
2. Irreversible
3. Allosteric 

1.Reversible Inhibition– binds through non-covalent bonds and activity of enzyme is restored. Divided into-

a) Competitive inhibitor– Km increased, Vmax unchanged.

E.g.- Succinate dehydrogenase by melanate.

b) Non competitive inhibitor- Km unchanged, Vmax decrease, mostly irreversible.

E.g.- Cyanide by Cytochrome C Oxidase.

Carbonic anhydrase by Acetazolamide

2. Irreversible Inhibition– binds covalently with an enzyme.

a) Suicidal Inhibitor– irreversible binding to enzyme and inhibit enzyme.

E.g. Allopurinol inhibit Xanthine oxidase, cyclooxygenase. 

3. Feedback Inhibition- called as end product inhibition.

E.g. AMP inhibits first step in purine synthesis.

Some enzymes, called allosteric enz,.mes, posses a site, in addition to substrate binding (catalytic) site, known as the allosteric site.
o Binding of allosteric modulator atthe allosteric site afiects the conformation of catalytic site.
o Such enzymes are called allosteric enzymes,
o The allosteric modulator (regulator) may facilitate the conformational change of catalytic site, required for substrate binding.
o Such regulators are called allosteric actirtators (positile allostefic modifier); for example, fructose-2, 6-bisphosphate is an al-losteric activator of Phosphofructokinase-I.
o Some allosteric regulators prevent the conformational change required for binding of the substrate.
o Such regulators are called allosteric inhibitors (negative allosteric modifier); for example, citrate is an allosteric inhibitor of phosphoructokinase-I