SYNTHESIS OF ALDOSTERONE BY MITOCHONDRIA AND HOMOGENEOUS 11-BETA-HYDROXYLASE FROM BEEF AND PIG

It was found that homogenous 11-beta-hydroxylase from bovine and porcine adrenals catalyzes the conversion of DOC to aldosterone. Mitochondria from both glomerulosa and fasciculata also convert DOC to aldosterone but glomerulosa is much more active than fasciculata. Cholate extracts of mitochondria from the two zones were equally active in converting DOC to aldosterone. Moreover all the enzyme activities of 11-beta-hydroxylase including 18-hydroxylation and aldehyde synthetase) were precipitated by a polyclonal antibody raised in rabbit against the pure 11-beta-hydroxylase. It is concluded that in beef and pig a single adrenocortical 11-beta-hydroxylase is responsible for the synthesis of aldosterone. To determine the influence of the mitochondrial membrane from glomerulosa and fasciculata on the activities of 11-beta-hydroxylase we examined the activities of rotenone-insensitive reductase enzymes in mitochondria from the two zones. Semidehydroxyascorbate reductase and NADH-cytochrome C reductase activities are considerably more active in glomerulosa than in fasciculata mitochondria. Moreover ascorbate plus NADH (but not ascorbate alone) greatly increases the ability of malate and NADPH to support synthesis of aldosterone without affecting 11-beta- or 18-hydroxylations in mitochondria. It is proposed that maximal synthesis of aldosterone by adrenocortical mitochondria requires in addition to the usual electron transport system (NADPH -> ADR -> ADX - ll-beta-OHase) an auxiliary system in the outer mitochondrial membrane: NADH -> Fp -> cyt b -> semidehydroascorbate reductase.