Analysis of the substrate inhibition of complete and partial types

A simple graphical method was described for determining the kinetic parameters of substrate inhibition of complete and partial types. The method consists of plotting experimental data as v/( Vₘₐₓ - v ) versus the reciprocals of the substrate concentrations, where V max represents the maximal velocity. The reaction rate constant of enzyme–substrate–inhibitor complex (k /k) can be calculated from the ordinate intercept of the linear relationship between v/( Vₘₐₓ - v ) and the reciprocal of the substrate concentrations at the higher and inhibitory concentrations of the substrate: partial type (k /k < 1) of the substrate inhibition gives straight lines intersecting with the ordinate at (k /k)/( 1- k /k) , whereas complete substrate inhibition (k = 0) yields straight lines converging on the origin. The Kᵢ value also can be calculated from the slope by using the k /k value determined. Validity of the method was confirmed by analyzing the substrate inhibition of phosphofructokinase II from E. coli. The present method provides a simple way for determining kinetic parameters of the substrate inhibition irrespective of complete and partial types.