The role of protein kinases in ACTH-stimulated steroidogenesis.

The effect of highly purified bovine cytosolic adrenal cortical protein kinase isozyme II catalytic subunit (ATP: Protein Phosphotransferase EC 2.7.1.37) on the formation of pregnenolone from cholesterol in rat and bovine adrenal mitochondrial extracts has been investigated. No stimulation was observed although a low level incorporation of ³²P] from ³²P]-ATP into a component or components of the extract was detected. The mitochondrial extracts contained alkaline phosphatase activity that was inhibited by L-cysteine and dithiothreitol. It is concluded that the acute stimulation by ACTH of corticoid production in the rat adrenal does not involve protein kinase mediated phosphorylation of a component or components of the cholesterol sidechain cleavage mixed-function oxygenase system.