NEW METHOD OF EVALUATION OF THE KINETIC-PARAMETERS OF BI-EXPONENTIAL ENZYME-CATALYZED REACTIONS

In many enzyme-catalyzed reactions the monitored time-course of the co ncentration of a product or an intermediate is bi-phasic, e.g. due to competing reactions or oxidation. The exact evaluation of such curves can be difficult with the conventional methods. However, we propose a quick and easy method of evaluation of the parameters of the bi-expone ntial equations that fit such progress curves of enzymatic process. Th e method is based upon the estimation by numerical integration of the area enclosed by the progress curve and one or two straight lines, dep ending on the case. This area can be obtained using almost any mathema tical commercial software for personal computers. With this area and a linear regression, the values of the parameters can be obtained. In t he cases in which we prefer to fit the progress curves by non-linear r egression, this method can be useful, since the values obtained for th e parameters can be used as an initial estimate for a subsequent non-l inear regression. Some cases have been studied and several examples us ing calculated curves with added experimental errors are presented to illustrate the applicability of the method. Finally, we have compared the results obtained with our method and other techniques described in the literature. We conclude that the new method compares favorably wi th those used previously, e.g. double regression and the method based on the maximal value, and is particularly useful in cases in which the data is scarce and the experimental error is high. (C) 1998 Elsevier Science Ltd. All rights reserved.