title: The enzymatic mechanism of glucuronidation catalyzed by two purified rat liver steroid UDP-glucuronosyltransferases.
abstract: A kinetic analysis of two homogeneous rat liver steroid (3 alpha-hydroxysteroid and 17 beta-hydroxysteroid) UDP-glucuronosyltransferases was conducted using bisubstrate kinetic analysis, product inhibition studies, and dead-end competitive inhibition studies. Double reciprocal plots of initial velocity versus substrate concentration, using bisubstrate kinetic analysis, gave a sequential mechanism. Product inhibition studies were compatible with either a rapid equilibrium, random-order kinetic mechanism or an ordered Theorell-Chance mechanism. Results of dead-end competitive inhibition studies excluded an ordered Theorell-Chance mechanism. The cumulative results are consistent with a rapid equilibrium random-order sequential kinetic mechanism for the glucuronidation of testosterone by purified 17 beta-hydroxysteroid UDP-glucuronosyltransferase and of androsterone by purified 3 alpha-hydroxysteroid UDP-glucuronosyltransferase.
mesh_terms: D000738:Androsterone / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D005260:Female; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D013739:Testosterone / Q000378:metabolism; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism*; D014539:Uridine Diphosphate Sugars / Q000378:metabolism*
chemical_list: D014539:Uridine Diphosphate Sugars; D014535:Uridine Diphosphate Glucuronic Acid; D013739:Testosterone; D000738:Androsterone; D014453:Glucuronosyltransferase