Abstract
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 [Formula: see text] versus the reciprocals of the substrate concentrations, where V max represents the maximal velocity. The reaction rate constant of enzyme-substrate-inhibitor complex [Formula: see text] can be calculated from the ordinate intercept of the linear relationship between [Formula: see text] and the reciprocal of the substrate concentrations at the higher and inhibitory concentrations of the substrate: partial type [Formula: see text] of the substrate inhibition gives straight lines intersecting with the ordinate at [Formula: see text], whereas complete substrate inhibition [Formula: see text] yields straight lines converging on the origin. The [Formula: see text] value also can be calculated from the slope by using the [Formula: see text] 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.