engleski

Michaelis constants for the EDTA-sensitive and EDTA-insensitive hydrolysis of paraoxon and phenylacetate by human esterases

The hydrolysis of paraoxon and phenylacetate by human serum esterases was measured in 0.1 M Tris/HCl buffer pH=8.4 in the absence (Vtot activity) and in the presence of 1.0 mM EDTA (Vins activity). The difference Vtot -Vins represents the EDTA-sensitive activity (Vsen). The Km for the paraoxon hydrolysis was the same at both pH values and for both, the EDTA-sensitive and EDTA-insensitive, enzyme: Km=0.67 mM. The Km for the EDTA-sensitive hydrolysis of phenylacetate was 0.83 mM (at both pH values) and for the EDTA-insensitive hydrolysis 2.6 mM (at both pH values). However, for both substrates the Vmax constants of the EDTA-insensitive enzymes were higher at pH=8.4 than at pH=7.4. : for the paraoxon hydrolysis 4.5-fold and for the phenylacetate hydrolysis 1.8-fold. The Vmax constants for the EDTA-sensitive hydrolysis of both substrates remained unaffected by the pH of the medium.

human serum esterases; paraoxon; phenylacetate; Michaelis constant

nije evidentirano