The influence of pH and inhibitors on the kinetics of enzyme reactions involving two intermediates

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Abstract
General steady-state equations are worked out for enzyme reactions which occur according to the scheme [image]. Equations showing the pH dependence of the kinetic parameters are developed in a form which distinguishes between essential and non-essential ionizing groups. The pK dependence of [image]c/[image]m, the second order constant extrapolated to zero substrate constant, given pK values for groups which ionize on the free enzyme, but reveals such a pK only if the corresponding group is also involved in the breakdown of the Michaelis complex. General steady-state equations are also developed for the case in which an inhibitor can combine with the free enzyme, the enzyme-substrate complex, and also a second intermediate (e.g. an acyl enzyme). The equations are given in a form that is convenient for analyzing the experimental results, and a number of special cases are considered. It is shown how the type of inhibition depends not only on the nature of the inhibitor but also on that of the substrate, an important factor being the rate-determining step of the reaction. Examples of the various kinds of behavior are given.