Activation of Succinate Dehydrogenase by Anions and pH

Succinate dehydrogenase in the deactivated form becomes activated on incubation at mildly acid pH to an extent dependent on the pH, type of anion present, and the concentration of the anion. The equilibrium level established under one set of conditions can be perturbed by changing either the pH or the anion concentration and the resulting level of activation reflects the new set of conditions. The rate of activation is influenced by the temperature, the anion concentration, and the pH when simple anions (e.g. Br-) are used, but the energy of activation is not affected by either pH or anion concentration. The value found for the activation energy (Ea) is 25 Cal per mole. In contrast, when activation of the enzyme is mediated by succinate, malonate, or reduced coenzyme Q10, the Ea value is 31 to 33 Cal per mole. Although this difference in energies of activation suggests that activation by mild acid and anions involves a different mechanism, no difference in the catalytic activity of preparations activated by these different methods is detected.