Succinic and reduced diphosphopyridine nucleotide oxidase systems of Ascaris muscle.

Although Ascaris lumbricoides, an adult intestinal nematode of the pig, lives in a habitat in which the oxygen tension is extremely low, considerable amounts of oxygen are taken up if the parasite is exposed to an aerobic environment (1, 2). Experiments with intact worms, homogenates, and particulate preparations confirmed these observations and demonstrated that oxygen uptake is dependent markedly upon the oxygen tension and results in the formation of HzOz (3, 4). Furthermore, oxidation of succinate occurs despite the absence of detectable amounts of cytochrome c and cytochrome oxidase and is stimulated by the addition of Mn++ (4). These results suggested that the terminal oxidase of adult Ascaris is a metal-catalyzed flavoprotein enzyme. An increasing body of evidence indicates that Ascaris is not unique among organisms with a mechanism of electron transport different from the classical cytochrome system of mammalian tissues; examples are found in some other helminth parasites (4), in certain bacteria (5), and in other organisms (6). Although the terminal step of respiration in Ascaris was investigated in the case of the oxidation of succinate, little information is available for diphosphopyridine nucleotide-linked enzymes or for the mechanisms concerned with electron transport from substrate to oxygen which operates in the absence of a detectable cytochrome system. The present investigation deals with the characteristics and interactions of the electron transport system that catalyzes the oxidation of succinate and DPNH in Ascaris muscle. The results suggest that electron transport from both substrates occurs through the participation of flavin enzymes, and that a coupling of these systems results in the rapid anaerobic reduction of fumarate by DPNH.