Mitochondrial NADH oxidase activity of adult Hymenolepis diminuta (Cestoda).

1. Mitochondria from adult Hymenolepis diminuta displayed a membrane-associated, rotenone-sensitive NADH oxidase and NADH-dependent fumarate reductase system. 2. Both the H. diminuta oxidase and fumarate reductase were relatively insensitive to antimycin A. potassium cyanide and sodium azide, at concentrations which significantly inhibited the NADH oxidase system of rat liver. 3. Malonate effectively depressed the mitochondrial NADH oxidase activity of both H. diminuta and adult Ascaris suum (Nematoda). 4. An involvement of Mn2+ ion, in NADH utilization by the H. diminuta oxidase, was apparent. 5. The utilization of NAD(P)H by H. diminuta, mitochondrial membranes resulted in hydrogen peroxide formation. Succinate utilization also resulted in peroxide accumulation but at a much slower rate than that found for NAD(P)H.