Absence of electron transport (Rho 0 state) restores growth of a manganese-superoxide dismutase-deficient Saccharomyces cerevisiae in hyperoxia. Evidence for electron transport as a major source of superoxide generation in vivo.
To address the possibility that electron transport is a biologically significant source of superoxide anion (O2-.) during exposure to hyperoxia in vivo, we constructed Saccharomyces cerevisiae strains with selective disruptions in the gene encoding the mitochondrial manganese-containing superoxide dismutase (Mn-SOD) and/or genes encoding proteins critical for complexes in electron transport. We hypothesized that complete absence of electron transport would restore growth in hyperoxia to a Mn-SOD-deficient yeast. We found that yeast deficient in Mn-SOD activity failed to grow normally in hyperoxia (95% O2, 5% CO2). In contrast, Mn-SOD-deficient yeast with complete absence of electron transport (the Rho 0 state) grew normally in hyperoxia. By comparison, Mn-SOD-deficient yeast which were deficient only in cytochrome-c-oxidase, the terminal step in electron transport, had only partially restored growth in hyperoxia. Our results indicate that electron transport is a major source of O2-. in vivo, and that the principal site of this O2-. production is proximal to the cytochrome-c-oxidase complex.
Guidot
D M
DM
Webb-Waring Institute of Biomedical Research, Denver, Colorado 80262.
McCord
J M
JM
Wright
R M
RM
Repine
J E
JE
D004579:Electron Transport; D008928:Mitochondria / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism*
D013482:Superoxide Dismutase; D010100:Oxygen