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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.

1987; Elsevier BV; Volume: 262; Issue: 12 Linguagem: Inglês

10.1016/s0021-9258(18)45591-3

1083-351X

Shanker Japa, Qin‐shi Zhu, Diana S. Beattie,

Photosynthetic Processes and Mechanisms

The functional role and topographical orientation in the inner membrane of subunit VII, the ubiquinonebinding protein, of the cytochrome b-cl 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 Qbinding proteins present in the cytochrome b-cl complexes isolated from both beef heart and yeast mitochondria.The specific antibody obtained against subunit VI1 inhibited 30-47% of the ubiquinol-cytochrome c reductase activity in the isolated cytochrome b-cl 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 VI1 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 0. These results suggest that subunit VII, the Q-binding protein, is involved in electron transport at center o of the cytochrome b-cl complex of the respiratory chain and that subunit VI1 is localized facing the matrix side of the inner mitochondrial membrane.The cytochrome b-cl complex, an enzyme complex of the inner mitochondrial membrane, catalyzes electron transport from ubiquinol to cytochrome c, coupled to ATP synthesis and ion transport.Cytochrome b-cl complexes isolated from beef heart (1, Z), rat liver (3), Neurospora crmsa (4), and yeast ( 5 , 6) mitochondria have been resolved after SDSl-polyacrylamide gel electrophoresis into 8-11 polypeptides of molecular weights ranging from 55,000 to 4,000.Three subunits of the