REGULATION OF CHOLESTEROL-METABOLISM IN ADRENAL-CORTEX - EFFECTS OF APOPROTEINS ON CHOLESTEROL ESTERASE IN RAT ADRENAL-GLANDS

We have investigated the effects of apoproteins on cholesterol esteras e (CEase) in rat adrenal glands in order to clarify the mechanism of s ynthesis of free cholesterol which is the most important substrate for steroidogenesis. We prepared lipid mixtures containing cholesteryl ol eate plus apoproteins with and without phosphatidylcholine as a substr ate for CEase in order to investigate the effect of the substrate stat e on CEase. The substrate containing only cholesteryl oleate and apo-H DL increased both acid and alkaline CEase activities. Both acid and al kaline CEase activities were also increased by a substrate containing apo-HDL plus cholesteryl oleate and phosphatidylcholine more than by a substrate containing cholesteryl oleate plus apo-LDL with phosphatidy lcholine or cholesteryl oleate with phosphatidylcholine. We have alrea dy reported that phosphatidylcholine is an important factor for the re gulation of adrenal CEase. Therefore, the present studies show that ap oproteins as well as phosphatidylcholine may be important factors for the regulation of adrenal CEase.