Analytical aspects of enzyme reversible inhibition

•Determination of the type of inhibition and estimation of I50 by using the degree of inhibition.•Ability to compare the values of I50 measured from different laboratories employing the same enzyme but different concentrations of substrate.•Evaluation of relative error of inhibitor concentration in the whole range of degree of inhibition.•Application of the proposed approach in the inhibition study of previous published works.

A simple graphical method for the determination of reversible inhibition type, inhibition constant (KiKi) and estimation of fifty percent of inhibition I50I50 of an enzyme reaction is described. The method consists of plotting experimental data as “degree of inhibition” versus the inhibitor concentration at two or more concentrations of substrate. Diagnosis of inhibition type is based on determination ofI50 and the observation of the shift of the inhibition curves. Relationship between I50and inhibition constant KiKi was discussed. A simplified hyperbolae equation of degree of inhibition showing kinetic orders of 1 and zero at low and high concentrations of inhibitors respectively is proposed. The relative error of inhibitor concentration increased drastically when degree of inhibition reached values of 90%. Examples of published inhibition reports as well as an experimental example of amperometric biosensor based on tyrosinase inhibition by benzoic acid were in agreement with the proposed theoretical approach.