Synthesis of Aldosterone by a Reconstituted System of Cytochrome P-45011β from Bovine Adrenocortical Mitochondria1

Abstract

When corticosterone was incubated with cytochrome P-450_11β purified from bovine adrenocortical mitochondria in the presence of adrenodoxin, NADPH-adrenodoxin reductase and an NADPH generating system, aldosterone as well as 18-hydroxy-corticosterone were formed with turnover numbers of 0.23 and 1.1 nmol/min/nmol P-450_11β, respectively. Phospholipids extracted from adrenocortical mitochondria remarkably enhanced the activity of aldosterone formation by the cytochrome P-450_11β-reconstituted system. The apparent K_m and turnover number were estimated to be 6.9 μM and 2.0 nmol/min/nmol P-450 for aldosterone formation in the presence of the lipidic extract. When 18-hydroxycorticosterone was tested as a substrate, cytochrome P-450_11β showed catalytic activity for aldosterone synthesis with an apparent Km and turnover number of 325 μM and 5.3 nmol/min/nmol P-450, respectively. Carbon monoxide and metyrapone inhibited the production of aldosterone from corticosterone and that from 18-hydroxycorticosterone. These results suggest that conversion of corticosterone and of 18-hydroxycorticosterone to aldosterone occurs through P-450_11β-catalyzed reaction.