title: The O2-dependence of respiration and H2O2 production in the parasitic nematode Ascaridia galli.
abstract: 1. Respiration in the parasitic nematode worm Ascaridia galli was inhibited at O2 concentrations in excess of 255 microM, and an apparent Km,O2 of 174 microM was determined. 2. Mitochondria-enriched fractions isolated from the tissues of A. galli have much lower apparent Km,O2 values (approx. 5 microM). They produce H2O2 in the energized state; higher rates of H2O2 production were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. 3. Antimycin A inhibited respiration in muscle tissue mitochondria by 10%, but had no effect on respiration in gut + reproductive tissue mitochondria; the major portion of respiration in both types of mitochondria could be attributed to an alternative electron-transport pathway. 4. o-Hydroxydiphenyl, an inhibitor of alternative electron-transport pathways, inhibits respiration by 98% and completely inhibits the production of H2O2 in gut-plus-reproductive-tissue mitochondria; respiration and H2O2 production in muscle tissue mitochondria were inhibited by 90 and 86% respectively. 5. Another inhibitor of alternative electron transport, salicylhydroxamic acid, had the same effect as o-hydroxydiphenyl on H2O2 production and respiration in gut-plus-reproductive-tissue mitochondria. However, its effect on muscle tissue mitochondria was complex; a low concentration (0.35 mM) stimulated H2O2 production, whereas 3 mM inhibited respiration by 87% and prevented H2O2 production completely. 6. The similarities between the apparent Km,O2 values for H2O2 production and respiration in muscle mitochondria and in gut-plus-reproductive-tissue mitochondria suggests that the site of H2O2 production on the alternative electron-transport chain is cytochrome 'o'. 7. These results are discussed in relation to potential O2 toxicity in A. galli.
authors.affiliation: Department of Microbiology, University College, Cardiff, Wales, U.K.
authors.forename: T A
authors.initials: TA
authors.lastname: Paget
authors.forename: M
authors.initials: M
authors.lastname: Fry
authors.forename: D
authors.initials: D
authors.lastname: Lloyd
mesh_terms: D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001197:Ascaridia / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects*; D012457:Salicylamides / Q000494:pharmacology
chemical_list: D012457:Salicylamides; D000968:Antimycin A; C005703:salicylhydroxamic acid; D006861:Hydrogen Peroxide; D010100:Oxygen