Succinate oxidase and fumarate reductase systems of filarial parasite Setaria digitata

Activities of succinate oxidase, fumarate reductase (FR) and succinate dehy drogenase (SDH) under a set of defined conditions were determined in the mi tochondrial isolate from Setaria digitata, the filarial parasite from the c attle Bos indicus. Presence of only two activities namely SDH and succinate - UQ reductase of the succinate oxidase system could be detected in S. dig itata. In the absence of cytochromes, the 3rd enzyme of the complex namely cytochrome oxidase is absent and it is proposed that an alternative oxidase is responsible for completing the succinate oxidation expressed as succina te oxidase activity. Though SDH and FR catalyse reverse reactions, they res ponded differently to modulators such as oxaloacetate, aspartate, alanine, pyruvate and fumarate. The degree of response of the two activities against inhibitors of electron transport was also different. Interestingly fumarat e caused only 50% inhibition of succinate oxidation, while the effect again st FR was more convincing.