<prompt> A drug that binds to receptor at a site distinct from the active site and alters the affinity of the receptor for the endogenous ligand is a:Competitive antagonistInverse agonistPartial agonistAllosteric modulator  <response>: Ref. KDT. Page. 59Competitive equilibrium type Allosteric modulatorThe drug being structurally similar competes with the normal substrate for the catalytic binding site of the enzymeThey increase the kM but the Vmax remains unchangedExamples:Physostigmine and neostigmine compete with acetylcholine for cholinesterase.Sulfonamides compete with P ABA for bacterial folate synthetase.  Moclobemide competes with catecholamines for monoamine oxidase-A MAO-A.  Captopril competes with angiotensin 1 for angiotensin converting enzyme ACE. 