Activation of succinate dehydrogenase from adult Fasciola hepatica (Trematoda).

The succinate dehydrogenase of adult Fasciola hepatica was found to exist in active and in active forms. The enzyme was inactivated by 1 micron oxaloacetate and activated by incubation with compounds which bind to the active site (succinate, fumarate, malonate) or by incubation with anions and certain nucleotides. The activation of the enzyme by succinate followed first-order kinetics. The extent of activation of F. hepatica succinate dehydrogenase depended on the nature and concentration of the activator and on the pH. The rate of activation of the enzyme depended on the temperature. In contrast, the fumarate reductase activity of F. hepatica was not activated by incubation with substrate or anions and was not inhibited by oxaloacetate (100 micron). The significance of these results in the regulation of the tricarboxylic acid cycle in parasitic helminths is discussed.