Kinetic analysis of modification reactions at comparable enzyme and modifier concentrations.

A method is proposed to determine the kinetic constants of enzyme modification where the condition of [Y0] >> [E0] is not satisfied, which is applicable to both inhibition and activation. This is a simple and rigorous one by which the apparent rate constants can be conveniently calculated, provided that the values of vo, vs, v* and [P]* are experimentally measured. The equations derived for the calculation of the apparent rate constants can be reduced to those obtained when [Y0] >> [E0]. Based on the expressions of the apparent rate constant and the apparent association constant, similar plotting methods can be applied to distinguish between the different competition types for both reversible and irreversible inhibitions.