Abstract
The temperature dependence of reactions catalyzed by alcohol dehydrogenase is measured. The activation energies are about 14 kcal/mol. The entropies of activation and association of both the substrates and the products are small. It is concluded that the enzyme does not undergo major structural changes in the course of the reaction, and that the substrates are attached in a rather rigid, crystal-like manner to the enzyme surface that activates the hydrogen transfer.The dependence of the kinetical data on pH suggests that this activation is partially brought about by hydrogen transfer over a hydrogen bridge between the alcohol and a basic group of the enzyme. This shift accelerates the reaction in analogy to general acid base catalysis by a factor 104–108. The dependence of the rate on the structure of the substrate indicates that the enzyme affects the methyl group of the alcohol. It is suggested that the enzyme activates, by a straining of the CH3 bond, the shift of the position of the methyl group that accompanies the change in the bond configuration in the alcohol molecule during the reaction. It seems that the influences of binding, bond straining and proton shifting by groups of the enzyme surface constitute the main catalytic effects of the enzyme.
