Localization of enzyme for heme attachment to apocytochrome c in yeast mitochondria.

Fractionation of yeast mitochondria by controlled hypotonic treatment revealed that the enzyme for heme attachment to apocytochrome c was localized in mitochondrial inner membrane. Trypsin digestion of mitoplasts resulted in a considerable loss of enzymatic activity, whereas the enzyme in intact mitochondria resisted the digestion. Triton X-100 solubilized the enzyme from the membrane but high concentration of salt did not. These results reveal that the enzyme for heme attachment is localized in mitochondrial inner membrane facing the cytoplasmic surface.