抄録
Experimental procedures and conditions for determination of kinetic constants of AChE inhibition by phenyl carbamate insecticides are reviewed. Experimentally determined dissociation equilibrium constant of the enzyme-inhibitor reversible complex, Kd, and the first order rate constant for the carbamylated enzyme formation, κ2, are shown to depend on the concentration of inhibitors in currently used procedures such as the Main method and the Hart and O'Brien's procedure in the presence of chromogenic substrate. The apparent Kd and κ2 values are virtually reproducible regardless of the procedures, if similar carbamate concentrations are used for the determination. Assuming that the further binding of carbamate molecules to the reversible complex and/or the carbamylated enzyme is significant with high inhibitor concentrations, “true” constants Kd and κ2 are obtainable with a rather low carbamate concentration range whose product by κ1 is of the order of 0.2-1.0min-1. For the decarbamylation rate constant κ3 which is usually determined upon dilution of the reaction mixture, the dilution factor should be selected according to the magnitude of Kd and κ2 and to the inhibitor concentration.
