Deletion of subunit 9 of the Saccharomyces cerevisiae cytochrome bc1 complex specifically impairs electron transfer at the ubiquinol oxidase site (center P) in the bc1 complex

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Abstract
Deletion of QCR9, the nuclear gene encoding subunit 9 of the mitochondrial cytochrome bc 1 complex in Saccharomyces cerevisiae, results in inactivation of the bc 1 complex and inabillity of the yeast to grow on non‐fermentable carbon sources. The loss of bc 1 complex activity is due to loss of electron transfer activity at the ubiquinol oxidase site (center P) in the complex. Electron transfer at the ubiquinone reductase site (center N), is unaffected by the loss of subunit 9, but the extent of cytochrome b reduction is diminished. This is the first instance in which a supernumerary polypeptide, lacking a redox prosthetic group, has been shown to be required for an electron transfer reaction within the cytochrome bc 1 complex.