Membrane topography of the subunits of ubiquinol – cytochrome‐c oxidoreductase of Saccharomyces cerevisiae

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Abstract
The topology of the subunits of ubiquinol–cytochrome‐c oxidoreductase of the yeast Saccharomyces cerevisiae has been determined using a digitonin/proteinase K assay. With this assay we were able selectively to disrupt the mitochondrial membranes and to identify the subunits which became proteinase‐K‐sensitive after disruption of either the outer or both outer and inner membranes. This approach confirmed previous indications for the localization of the core I protein, cytochrome c1, cytochrome b, the FeS protein and the 17‐kDa subunit, while it also provided direct evidence for the site of accessibility to proteinase K of the 14‐kDa and 11‐kDa subunits. The 14‐kDa subunit faces the mitochondrial matrix and the 11‐kDa subunit faces the intermembrane space.