title: Subunit VII, the ubiquinone-binding protein, of the cytochrome b-c1 complex of yeast mitochondria is involved in electron transport at center o and faces the matrix side of the membrane.
abstract: The functional role and topographical orientation in the inner membrane of subunit VII, the ubiquinone-binding protein, of the cytochrome b-c1 complex of yeast mitochondria has been investigated. The apparent molecular weight of this subunit on sodium dodecyl sulfate-urea gels was calculated to be 15,500, while its amino acid composition was similar to that of the Q-binding proteins present in the cytochrome b-c1 complexes isolated from both beef heart and yeast mitochondria. The specific antibody obtained against subunit VII inhibited 30-47% of the ubiquinol-cytochrome c reductase activity in the isolated cytochrome b-c1 complex and in submitochondrial particles but had no effect on cytochrome c reductase activity in mitoplasts, mitochondria from which the outer membrane has been removed. Furthermore, the antibody against subunit VII strongly inhibited (74%) the reduction of cytochrome b by succinate in the presence of antimycin, an inhibitor of center i, but had no effect on cytochrome b reduction in the presence of myxothiazol, an inhibitor of center o. These results suggest that subunit VII, the Q-binding protein, is involved in electron transport at center o of the cytochrome b-c1 complex of the respiratory chain and that subunit VII is localized facing the matrix side of the inner mitochondrial membrane.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000906:Antibodies; D000936:Antigen-Antibody Complex; D002352:Carrier Proteins / Q000378:metabolism*; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000378:metabolism*; D007425:Intracellular Membranes / Q000201:enzymology*; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D000596:Amino Acids; D000906:Antibodies; D000936:Antigen-Antibody Complex; D002352:Carrier Proteins; C027208:ubiquinone-binding proteins; D014450:Electron Transport Complex III