title: Hydrolysis of 4-nitrophenyl acetate catalyzed by carbonic anhydrase III from bovine skeletal muscle.
abstract: We report three experiments which show that the hydrolysis of 4-nitrophenyl acetate catalyzed by carbonic anhydrase III from bovine skeletal muscle occurs at a site on the enzyme different than the active site for CO2 hydration. This is in contrast with isozymes I and II of carbonic anhydrase for which the sites of 4-nitrophenyl acetate hydrolysis and CO2 hydration are the same. The pH profile of kcat/Km for hydrolysis of 4-nitrophenyl acetate was roughly described by the ionization of a group with pKa 6.5, whereas kcat/Km for CO2 hydration catalyzed by isozyme III was independent of pH in the range of pH 6.0-8.5. The apoenzyme of carbonic anhydrase III, which is inactive in the catalytic hydration of CO2, was found to be as active in the hydrolysis of 4-nitrophenyl acetate as native isozyme III. Concentrations of N-3 and OCN- and the sulfonamides methazolamide and chlorzolamide which inhibited CO2 hydration did not affect catalytic hydrolysis of 4-nitrophenyl acetate by carbonic anhydrase III.
mesh_terms: D000818:Animals; D001051:Apoenzymes / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D009596:Nitrophenols / Q000378:metabolism*
chemical_list: D001051:Apoenzymes; D002257:Carbonic Anhydrase Inhibitors; D007527:Isoenzymes; D009596:Nitrophenols; D002245:Carbon Dioxide; C008642:4-nitrophenyl acetate; D002256:Carbonic Anhydrases