A graphical method for extracting rate constants from some enzyme-catalyzed reactions not monitored to completion

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Abstract
A large number of enzyme-catalyzed reactions can be described by the equation y = At - B(1 - e-kt), where y is the amount of product formed. A is the slope of the linear portion of the curve, and B is a constant dependent on the mechanism of the reaction. The methods which are generally used to extract the rate constant, k, from absorbance - time data described by this equation require that the reaction be monitored for some 10-15 half-lives. The rate constant k is readily obtained from a plot of (y'''' - y'') vs. (y'' - yo) where y0, Y'' and Y'''' are the values of y at times t, t + .DELTA.t and t + 2.DELTA.t. This graphical method is simple, reliable and requires that the reaction be monitored for only 3-5 half-lives of the esponential phase of the reaction. This method was used to measure the rate of activation of a mised disulfide of papain and 2-nitro-5-mercaptobenzoic acid in the presence of substrate.

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