Electrophoretic analysis and cytochrome P450 contents of bovine adrenal cortex mitochondria and of their subfractions

Abstract

Adrenal cortex mitochondria were fractionated into outer membrane and inner membrane. This second membrane was further separated into water-soluble proteins, KCl extractable proteins, “structural proteins” and structured cytochromes. Cytochrome P450located in the inner membrane was found only in the structured cytochrome fraction. The protein components of all the fractions were analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Mitochondria contain at least 20 components ranging in molecular weight from 10,000–120,000 daltons. The outer membrane is different from the inner membrane both in number of components and size distribution. In structured cytochrome proteins a component of 52,000 molecular weight represents about 25% of the whole protein contents. This corresponds to the subunit of cytochrome P450. Proteins synthesized in isolated adrenal cortex mitochondria in the presence of radioactive leucine reveal six groups of labelled polypeptides when subjected to polyacrylamide gel electrophoresis. The molecular weights of these proteins ranged from 10,000–54,000 daltons. In the fraction of structured cytochromes a labelled component having a molecular weight 52,000 daltons was found. It is thought that this component may correspond to the subunit of cytochrome P450 and be coded partly by mitochondrial nucleic acids.