Search

To identify the common inhibition types, the putative decision system is unsatisfactory. In a new decision system, Michaelis-Menten constants and maximal reaction rates were plotted versus inhibitor concentrations for deriving Kik and Kiv as the inhibition constants, respectively; their difference was quantified as the ratio of the larger one to the smaller one. Such ratios below 2.0 suggested uncompetitive inhibitors, over 5.0 suggested noncompetitive or competitive inhibitors, and from 2.0 to 5.0 suggested mixed inhibitors. By the new decision system, (i) the simulation recovery of uncompetitive inhibitors under CVs of 2% or 5% was improved by four times, but that of competitive or noncompetitive inhibitors was improved slightly; (ii) the recovery of L-phenylalanine as an uncompetitive inhibitor of intestinal alkaline phosphatase reached 38%, while the putative decision system lost all; the recovery of xanthine as a competitive inhibitor of uricase was improved slightly. Therefore, the new decision system was better. [ABSTRACT FROM AUTHOR]

A new simple graphical method is described for the determination of inhibition type and inhibition constants of an enzyme reaction without any replot. The method consists of plotting experimental data as ( V– v)/ v versus the inhibitor concentration at two or more concentrations of substrate, where V and v represent the maximal velocity and the velocity in the absence and presence of inhibitor with given concentrations of the substrate, respectively. Competitive inhibition gives straight lines that converge on the abscissa at a point where [I] = − K i. Uncompetitive inhibition gives parallel lines with the slope of 1/ K’ i. For mixed type inhibition, the intersection in the plot is given by [I] = − K i and ( V–v)/ v = − K i /K’ i in the third quadrant, and in the special case where K i = K’ i (noncompetitive inhibition) the intersections occur at the point where [I] = − K i and ( V– v)/ v = −1. The present method, the “quotient velocity plot,” provides a simple way of determining the inhibition constants of all types of inhibitors. [ABSTRACT FROM AUTHOR]