Import and processing of P-450 scc and P-450 11 β precursors by corpus luteal mitochondria: A processing pathway recognizing homologous and heterologous precursors

Abstract

Maturation of the precursor forms of bovine cholesterol side-chain cleavage cytochrome P-450 ( P-450 scc) and 11β-hydroxylase cytochrome P-450 ( P-450 11 β ) was investigated using mitochondria from bovine corpus luteum. The results show that both precursors, whose synthesis was directed by bovine adrenocortical RNA, can be imported and proteolytically processed to their corresponding mature forms by bovine corpus luteal mitochondria, even though P-450 11 β is not expressed in this tissue. Furthermore, the efficiency of processing of pre- P-450 11β by corpus luteal mitochondria is similar to that of pre- P-450 scc , an endogenous enzyme of these mitochondria. However, the P-450 11 β precursor is not processed by mitochondria from a nonsteroidogenic tissue (heart), a result observed previously for the P-450 scc precursor (M. F. Matocha and M. R. Waterman (1984) J. Biol. Chem. 259, 8672–8678) . This discriminatory processing of pre- P-450 11β by heterologous mitochondria suggests that the precursor forms of P-450 scc and P-450 11 β are processed via a common pathway in steroidogenic mitochondria and that this pathway is absent in nonsteroidogenic mitochondria.