Effects of Temperature on Enzyme Reactions

The thermodynamic treatment for the temperature dependence of simple chemical reactions, discussed in Chapter 2 (Section 2.6), applies equally well to enzyme-catalyzed reactions, but in practice several complications arise that must be properly understood if any useful information is to be obtained from temperature-dependence studies of enzyme reactions. 

almost aU enzymes become denatured if they are heated much above physiological temperatures and the conformation of the enzyme is altered, often irreversibly, with loss of catalytic activity. Exceptions are the thermophylic microorganisms, which are capable of working within a much broader range of temperature. The loss of catalytic activity if often due to denaturation denaturation is chemically a very complex process, considering a large molecular size of proteins and the complexity of their three-dimensional stracture. 

The second influence of temperature is a usual influence of temperature on the rate of chemical reactions. The major effect of temperature is often not only on rates of chemical reaction, but also on the possible conformation changes before and after the chemical step, since these may have larger standard Gibbs free energies of activation than the chemical steps. Because of the overlapping influence on the stracture of the protein molecule, straightforward analysis of the influence of temperature on the rates of enzyme-catalyzed reactions can be often obtained only within afairly small range of temperature, usually between o°C and 50 C. 

A special branch of enzymology, cryoenzymology, deals with enzyme reactions in mixed solvents at subzero temperatures (Douzou, 1977 Fink Greeves, 1979). 

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