Regulation of cytochrome P450 activities in adrenocortical mitochondria from normal rats and human neoplastic tissues.

From our immunocytochemical studies, cytochrome P450scc and P45011 beta systems were localized on the matrix side of inner membrane of the mitochondria in the parenchymal cells of adrenal cortex. However, the degree of immunocytochemical staining varied from one mitochondrion to another within a single cell; some stained intensely along the entire inner membrane, some stained only along segments of the inner membrane, and some did not stain at all. The ratio of stained to unstained mitochondria was approximately unity in untreated rats, while stained mitochondria greatly increased upon ACTH administration suggesting that the population of cytochrome P450 system-containing mitochondria increased upon long-term ACTH action. By the combined use of flash photolysis and substrate difference spectroscopy, quantitative determination of substrate-bound and free forms of P450scc and P45011 beta in mitochondria became possible. Increases in total amounts of P450scc and cholesterol resulted from the long-term ACTH administration to rats. The ratio of cholesterol-bound P450scc to its free form was essentially unchanged under these conditions. On the other hand, amounts of P45011 beta were not increased significantly by long-term ACTH administration. The ratio of DOC-bound P45011 beta to the free form increased significantly, however, by long-term ACTH administration and also in the mitochondria from patients suffering from Cushing's syndrome.