Enzyme Inhibition Types Quiz

Study Notes

Competitive inhibition happens when the inhibitor has structural similarity to the substrate.
The inhibitor and substrate compete to bind to the enzyme's catalytic site.
Competitive inhibition is reversible.
Increasing substrate concentration relieves the inhibition.
Competitive inhibition does not affect Vmax but increases Km.

Non-competitive inhibition occurs when the inhibitor has no structural similarity to the substrate.
The inhibitor binds to a site on the enzyme other than the catalytic site.
The inhibitor can bind to the free enzyme or the enzyme-substrate complex.
Non-competitive inhibition is generally irreversible.
Increasing substrate concentration does not relieve the inhibition.
Non-competitive inhibition decreases Vmax but does not affect Km.

Inhibition of sulphahydryl (-SH) groups: Many enzymes depend on free -SH groups for activity. Heavy metals (like mercury and lead) can inhibit these groups.
Coenzyme inhibition: Cyanide hydrazine inhibits the action of coenzymes like pyridoxal phosphate (PLP), crucial for reactions like transamination, decarboxylation, and deamination.
Prosthetic group inhibition: Carbon monoxide (CO) and cyanide block the iron in heme groups, inhibiting enzymes like cytochrome oxidase.
Metal ion activator inhibition: Chelating agents can block metal ions needed for enzyme activity. For example, oxalate chelates calcium ions, preventing blood clotting, and fluoride chelates magnesium ions, inhibiting glycolysis.

Gout treatment with allopurinol: Allopurinol inhibits xanthine oxidase, reducing uric acid levels, and thus treats gout, an accumulation of urate crystals.