NADH-fumarate reductase and succinate dehydrogenase activities in mitochondria of Ascaridia galli and Nippostrongylus brasiliensis

Abstract

1. 1. NADH-fumarate reductase, succinate dehydrogenase and succinate ubiquinone reductase activities have been assayed and compared in mitochondrial fractions from the parasitic nematodes Ascaridia galli and Nippostrongylus brasiliensis. Activities have been partially characterised with respect to pH, K m and the effect of standard inhibitors. 2. 2. NADH-fumarate reductase activity was assessed by spectrophotometric and radioisotopic methods. Specific activities were of the order of 40 nmol/min/mg protein in both A. galli and N. brasiliensis mitochondria, although the spectrophotometric assay was found to underestimate activity by as much as 70% in some cases. 3. 3. A. galli succinate dehydrogenase was competitively inhibited by fumarate. In N. brasiliensis however, only that succinate oxidase activity associated with the alternative electron transport pathway was appreciably inhibited by this compound. 4. 4. High and low values of K m succ were apparent for both succinate dehydrogenase and succinate oxidase of N. brasiliensis. The high value K m was similar to that given by the A. galli succinate dehydrogenase, whereas the low K m value was similar to that given by the rat liver enzyme. The low K m succinate dehydrogenase of N. brasiliensis is apparently associated with the mammalian-like respiratory pathway and is not appreciably inhibited by fumarate. 5. 5. No firm conclusions can be drawn as to whether fumarate reductase and succinate dehydrogenase of A. galli mitochondria are the same or different enzymes. However, results do suggest the presence of two distinguishable succinate dehydrogenases in N. brasiliensis mitochondria.