Import of proteins into mitochondria. Cytochrome b2 and cytochrome c peroxidase are located in the intermembrane space of yeast mitochondria.

Yeast mitochondria were fractionated into inner membrane, outer membrane, matrix, and intermembrane space. Identity and purity of each fraction were monitored by enzyme assays, dodecyl sulfate-polyacrylamide gel electrophoresis, and immunological detection of characteristic mitochondrial polypeptides. Cytochrome b2 and cytochrome c peroxidase were found to be components of the intermembrane space. The most reliable marker of the outer membrane was a major 29,000-dalton polypeptide component. The availability of submitochondrial fractions provides a basis for studying import of precursor polypeptides into isolated yeast mitochondria.