ABSTRACT
Enzyme activity is commonly expressed by the initial rate of the reaction being catalyzed. The normal pattern of dependence of enzyme rate on substrate concentration ([S]) is that at low substrate concentrations a doubling of [S] will lead to a doubling of the initial velocity. Temperature affects the rate of an enzyme-catalyzed reaction by increasing the thermal energy of the substrate molecules. This increases the proportion of molecules with sufficient energy to overcome the activation barrier and hence increases the rate of the reaction. Each enzyme has an optimum pH at which the rate of the reaction that it catalyzes is at its maximum. Small deviations in pH from the optimum value lead to decreased activity due to changes in the ionization of groups at the active site of the enzyme. The enzyme (E), combines with its substrate (S) to form an enzyme–substrate complex (ES).
