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Hydrolysis of malathion by rabbit liver oligomeric and monomeric carboxylesterases

1983; Elsevier BV; Volume: 20; Issue: 2 Linguagem: Inglês

10.1016/0048-3575(83)90028-7

1095-9939

Paul T. Lin, A. R. Main, N. Motoyama, W.C. Dauterman,

Pesticide Exposure and Toxicity

The hydrolysis of malation by rabbit liver oligomeric and monomeric carboxylesterases (CE's) (EC 3.1.1.1) results in the formation of a mixture of α- and β-monoacids. A new chromatographic procedure was utilized to investigate the formation of α- and β-monoacids. The oligomeric carboxylesterase (oCE) produced an αβ ratio of monoacids of 4.55, and the monomeric carboxylesterase (mCE) produced an αβ ratio of monoacids of 2.33. The ratios of α- and β-monoacids were independent of the initial concentration of malathion and remained constant over the time course of the reaction. Kinetic studies demonstrated that the Km values were the same for the corresponding reactions which produced either α-monoacid or β-monoacid with the same enzyme. Since both carboxylesterases are electrophoretically pure, the kinetic data strongly supports the theory that the reactions which produced α- and β-monoacids are catalyzed by the same active site. Comparison of the kcat and Km values governing the hydrolysis of malathion by the two esterases, together with their relative abundance in liver, indicated that the oCE would be responsible for about 80 to 98% of the hydrolytic detoxication of malathion by rabbit liver.