New method of evaluation of the kinetic parameters of bi-exponential enzyme-catalyzed reactions

Abstract

In many enzyme-catalyzed reactions the monitored time-course of the concentration 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-exponential equations that fit such progress curves of enzymatic process. The method is based upon the estimation by numerical integration of the area enclosed by the progress curve and one or two straight lines, depending on the case. This area can be obtained using almost any mathematical commercial software for personal computers. With this area and a linear regression, the values of the parameters can be obtained. In the cases in which we prefer to fit the progress curves by non-linear regression, this method can be useful, since the values obtained for the parameters can be used as an initial estimate for a subsequent non-linear regression. Some cases have been studied and several examples using 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 with 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.