A potassium-induced mitochondrial protein related to aldosterone biosynthesis

Late steps of aldosterone biosynthesis, i.e., the conversions of corticosterone to 18-hydroxycorticosterone and aldosterone, are catalyzed by a mitochondrial cytochrome P-450. Resumption of potassium intake by potassium-depleted rats resulted within 2 days in a marked stimulation of these conversions, as reflected by increased production of aldosterone and 18-hydroxycorticosterone and decreased outputs of deoxycorticosterone, corticosterone, and 18-hydroxy-11-deoxycorticosterone by incubated capsular portions of the adrenal glands. The stimulation of aldosterone biosynthesis was accompanied by the appearance of a protein with a molecular weight of about 49,000 in the mitochondria of the zona glomerulosa but not of the inner zones of the adrenal cortex. Over 48 h of potassium repletion, the amount of this protein increased in parallel with the activity of the final steps of aldosterone biosynthesis. According to its molecular weight, its zone specificity, and the time course of its appearance, this protein might represent the steroid 18-methyl oxidase (cytochrome P-450CMO for corticosterone methyl oxidase) that catalyzes the conversion of corticosterone to 18-hydroxycorticosterone and aldosterone.