End-Point and Kinetic Readouts

The initial velocity of reaction is defined by the slope of a linear plot of product (or substrate) concentration as a function of time (Chapter 2), and we have just discussed the importance of measuring enzymatic activity during this initial velocity phase of the reaction. The best measure of initial velocity is thus obtained by continuous measurement of product formation or substrate disappearance with time over a convenient portion of the intial velocity phase. However, continuous monitoring of assay signal is not always practical. Copeland (2000) has described three types of assay readouts for measuring reaction velocity continuous assays, discontinuous 

The underlying assumption in any end-point assay is that the time point measured is well within the initial velocity phase of the reaction, so that product formation or substrate disappearance is a linear function of time. If this is true, then the 

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