Contributions of cytoplasmic free and membrane-bound ribosomes to the synthesis of mitochondrial cytochrome P-450(SCC) and P-450(11 beta) and microsomal cytochrome P-450(C-21) in bovine adrenal cortex.

Rabbit antibodies against cytochrome P-450 (SCC), P-450 (11 beta), and P-450 (C-21) from bovine adrenal cortex were prepared, and it was confirmed that these three cytochrome P-450 species are immunologically distinct from one another. Cytoplasmic sites of synthesis of P-450 (SCC), P-450 (11 beta), and P-450 (C-21) in bovine adrenal cortex were determined by examining the presence of their nascent peptides on isolated free and bound ribosomes. Nascent peptides were released in vitro from ribosomes by [3H]puromycin in a high salt buffer in the presence of a detergent, and the nascent peptides of P-450 (SCC), P-450 (11 beta), and P-450 (C-21) were isolated by immunoprecipitation. The nascent peptides of these three cytochrome P-450 species were found in both free and bound ribosomal fractions, suggesting that they share common sites of synthesis in the cytoplasm. However, the nascent peptides of mitochondrial P-450 (SCC) and P-450 (11 beta) were more concentrated in the free ribosomal fraction, whereas those of microsomal P-450 (C-21) were more abundant in the bound ribosomal fraction. The nascent peptides of the three cytochrome P-450 species were released from the membrane-bound ribosomes of rough microsomes into the cytoplasmic surface of microsomal vesicles by puromycin treatment.