Mitochondrial Heterogeneity in the Parasitic Nematode, Ascaris suum

Abstract

The anaerobic metabolism of Ascaris suum body wall muscle mitochondria has been well characterized, but little is known about the metabolism of other adult tissues. The present study was designed to further characterize the metabolism of mitochondria isolated from A. suum male reproductive tissues, which contain predominately sperm, and to compare it with that of muscle. Cytochrome oxidase activity could not be detected in muscle, testis, or sperm mitochondria either by diaminobenzidine staining or enzymatic assays. However, the activities of several tricarboxylic acid cycle enzymes, including citrate synthase and isocitrate dehydrogenase, were about 100- fold higher in testis/seminal vesicle mitochondria than muscle mitochondria. In contrast, malic enzyme activity in testis/seminal vesicle mitochondria was about 12-fold lower than that in muscle mitochondria. The incorporation of 32Pi into organic phosphate by either muscle or testis/seminal vesicle mitochondria appeared to be dependent on malate and pyruvate, and incorporation was inhibited by rotenone but not cyanide. Thus, the metabolism of testis/seminal vesicle mitochondrial preparations appears to be similar to that of ascarid muscle, despite the elevated levels of tricarboxylic acid cycle enzyme activities present in testis/seminal vesicle mitochondria. The function of these elevated enzymes is unclear, but the possibility that they are used later in the aerobic metabolism of the fertilized egg has not been excluded.