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:

Ref. KDT. Page. 59 Competitive (equilibrium type –Allosteric modulator) The drug being structurally similar competes with the normal substrate for the catalytic binding site of the enzyme They increase the kM but the Vmax remains unchanged Examples: 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).