3.2.3. pH and Temperature Dependence
pH Effect. Each enzyme has a characteristic pH optimum at which its activity is at a maximum. In the range of this optimum essential proton-donating or proton-accepting groups in the active center of the enzyme are in the ionized state required for the enzyme to function. Outside this range, substrate binding is no longer possible, and at extreme pH values the enzyme may be irreversibly denatured. The pH optimum depends on the composition of the medium, the temperature, and the enzyme's stability in acid and alkaline environments. The pH stability does not necessarily coincide with the pH optimum of the reaction rate.
Temperature Effect. As with all chemical reaction rates, those of enzyme reactions increase with increasing temperature (by a factor of 1.4 - 2.0 per 10 K), a limit being set by the thermal stability of the protein. The optimum temperature may be in a wide range, roughly between 30 and 80°C.