IN VITROINHIBITION OF SUCCINATE OXIDATION BY ALFALFA SAPONIN

Abstract

The effect of various levels of alfalfa saponin on the in vitro oxidation of succinate by rat liver homogenates was examined. With levels of 1 to 30 mg saponin per 100 mg liver tissue, the degree of inhibition increased from 3 to 90%. The inhibition was noncompetitive, since it was not overcome by increasing the substrate concentration. Mitochondria isolated from homogenates which had been incubated with saponin exhibited a reduced capacity to oxidize succinate of about the same magnitude as observed when saponin was added directly to the homogenates in the reaction vessels. Since the procedure for isolation of mitochondria should remove any unbound saponin, the reduction in oxidation capacity was attributed to binding of saponin to the succinoxidase enzyme. Thus, cumulative effects of saponin on enzyme activity might occur in vivo. Ethanol extracts of alfalfa were also found to inhibit in vitro succinate oxidation. Evidence is presented indicating that the inhibitory activity of these extracts was not due to their saponin content. Possible implications of the inhibition of succinate oxidation by alfalfa saponin are discussed.