What is Inhibitors?

An inhibitor lowers the rate of an enzyme. Irreversible inhibitors bind covalently and destroy the enzyme’s activity for good (nerve agents on acetylcholinesterase, penicillin on the enzyme that cross-links the bacterial wall, aspirin on the enzyme that makes prostaglandins). Reversible inhibitors bind by weak bonds and can be washed away; by where they bind:

• competitive: the inhibitor resembles the substrate and occupies the active site; it raises the apparent $K_m$ (by the factor $1 + [I]/K_i$) and leaves $V_{\max}$ unchanged — enough substrate displaces it;
• non-competitive: the inhibitor binds elsewhere and spoils the catalysis whether or not substrate is bound; it lowers $V_{\max}$ and leaves $K_m$ unchanged — no amount of substrate overcomes it;
• uncompetitive: the inhibitor binds only the $ES$ complex; both $V_{\max}$ and $K_m$ fall.

$K_i$, the dissociation constant of the inhibitor, measures its potency: the lower, the stronger.