title: Effect of alcohols on the hydrolysis catalyzed by human pancreatic carboxylic-ester hydrolase.
abstract: Transfer reactions catalyzed by human pancreatic carboxylic-ester hydrolase (EC 3.1.1.1) were studied in the presence of methanol and butanol as nucleophiles. The addition of alcohols produced an increase in the total rate of 4-nitrophenyl acetate and n-propylthiol acetate disappearance and a concomitant slow decrease of the hydrolysis rate. These results indicate a competitive partitioning of an acyl-enzyme intermediate between water and nucleophile. Moreover, a strong inhibition of the rates of hydrolysis of methyl butyrate and triacetin by nucleophiles is in agreement with a rate-limiting acylation step. The kinetic data and a trans-ester characterization argue in favor of the formation of an acyl-enzyme intermediate and a two-step reaction mechanism, acylation and deacylation both being rate-limiting. The experiments performed with 4-nitrophenyl acetate show the existence of a nucleophile binding site.
mesh_terms: D020001:1-Butanol; D000440:Butanols / Q000494:pharmacology*; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008433:Mathematics; D000432:Methanol / Q000494:pharmacology*; D010179:Pancreas / Q000201:enzymology*; D010189:Pancreatic Juice / Q000201:enzymology; D013379:Substrate Specificity
chemical_list: D000440:Butanols; D020001:1-Butanol; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D000432:Methanol