Subunit 8 of theSaccharomyces cerevisiae cytochromebc1 complex interacts with succinate-ubiquinone reductase complex
We have investigated the function of subunit 8 of the cytochromebc1 complex by generating six site-directed mutants, F46C, R51S, P62V, G64A, R91N, and W69-stop, in the clonedQCR8 gene and expressing the mutated genes in aSaccharomyces cerevisiae strain in which the chromosomal copy ofQCR8 is deleted. The W69-stop mutation impairs assembly of thebc1 complex and growth of yeast on nonfermentable carbon sources as does deletion ofQCR8 [Maarse, A. C., De Haan, M., Schoppink, P. J., Berden, J. A., and Grivell, L. A. (1988).Eur. J. Biochem.172, 179–184], implying that the C-terminus of subunit 8 is important for assembly and/or the stability of thebc1 complex. The F46C, R51S, P62V, G64A, and R91N mutations do not affect the growth of yeast on nonfermentable carbon sources, not do they lower the activity or alter the inhibitor sensitivity of thebc1 complex. Rather, some of the mutations increase the cytochromec reductase activity of thebc1 complex by as much as 40%. However, succinate-ubiquinone reductase activity was consistently reduced 40–60% in mitochondrial membranes from these mutants, while NADH-ubiquinone reductase activity was not affected. In addition, the activation of succinate-ubiquinone reductase activity by succinate was diminished by the F46C, R51S, P62V, and G64A mutations. These results indicate that the cytochromebc1 complex participates in electron transfer from succinate to ubiquinonein situ and also suggest an interaction between succinate-ubiquinone reductase and cytochromebc1 complex which involves subunit 8 of thebc1 complex.
KeywordsOrganic Chemistry Carbon Source Electron Transfer Succinate Mitochondrial Membrane
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