title: NADH→NAD⁺ Transhydrogenation in Adult Ascaris suum Mitochondria.
abstract: Although lacking an NADPH→NAD(+) transhydrogenase system, the essentially energetically anaerobic mitochondria of the adult intestinal nematode Ascaris suum display an inner membrane-associated NADH→NAD(+) transhydrogenation reaction. This reaction is considered to be reflective of a mechanism(s) that acts in catalyzing a transmembrane translocation of reducing equivalents from NADH in the intermembrane space to matrix NAD(+), thereby forming matrix NADH that would serve in electron transport. Ascarid mitochondrial lipoamide dehydrogenase rather than an NADH→NAD(+) transhydrogenase system has been viewed as the predominant source of inner membrane-associated NADH→NAD(+) transhydrogenation activity. However, the present study made apparent yet another source of mitochondrial, inner membrane-associated NADH→NAD(+) activity in A. suum , viz., NADH dehydrogenase. This was made evident via comparisons of the A. suum mitochondrial NADH→NAD(+) transhydrogenation, NADH dehydrogenase, and lipoamide dehydrogenase activities in terms of pH effects, thermal labilities, the involvement of NADH dehydrogenase in the activities of mitochondrial, membrane-associated rotenone-insensitive and rotenone-sensitive NADH-dependent cytochrome c reductases, and mitochondrial membrane versus mitochondrial soluble localizations. Studies of the responses of the NADH→NAD(+) transhydrogenation, rotenone-insensitive and rotenone-sensitive cytochrome c reductases, and lipoamide dehydrogenase activities to inhibition by copper and cadmium lent additional support to the catalysis of an NADH→NAD(+) transhydrogenation activity by NADH dehydrogenase. Collectively, the data presented are consistent with an additional physiological catalysis of an NADH→NAD(+) transhydrogenation in A. suum mitochondria by an inner membrane NADH dehydrogenase component of the rotenone-sensitive cytochrome c reductase system, i.e., the NADH dehydrogenase component of the electron transport system. Comparisons of the A. suum data with those from other essentially anaerobic helminth parasites as well as free-living eukaryotic mitochondrial systems are noted.
authors.affiliation: Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403.
authors.forename: Andrew
authors.initials: A
authors.lastname: Holowiecki
authors.affiliation: Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403.
authors.forename: Carmen F
authors.initials: CF
authors.lastname: Fioravanti
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology; D017165:Ascaris suum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002104:Cadmium / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D006863:Hydrogen-Ion Concentration; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009250:NADP Transhydrogenases / Q000378:metabolism
chemical_list: D000871:Anthelmintics; D002104:Cadmium; D009243:NAD; D003300:Copper; D009250:NADP Transhydrogenases; D008058:Dihydrolipoamide Dehydrogenase