The 19-Hydroxylase of the Gerbil Adrenal Gland: A Mitochondrial Enzyme

Abstract

The adrenal gland of the Mongolian gerbil produces nearly equal amounts of 19-hydroxy- and 11.beta.-hydroxycorticosteroids. The intracellular location of the 19-hydroxylase (OHase) was studied by determining the activities of both the 19- and 11.beta.-OHase enzymes in gerbil adrenal homogenate and subcellular fractions. Adrenal preparations were incubated in vitro in the presence of exogenous steroid precursor, androstenedione (A), testosterone (T) or deoxycorticosterone (DOC), plus a source of reducing equivalents. When adrenal homogenate was incubated with A plus isocitrate, the only 2 products detected were 19-hydroxy A and 11.beta.-hydroxy A; the 2 were formed at virtually identical rates. With subcellular fractions, the capacity for 19-hydroxylation coincided with that for 11.beta.-hydroxylation; the highest activities were in adrenal mitochondria. For adrenal mitochondria the 2 hydroxylation reactions were enhanced by the addition of Ca2+ to incubations containing NADPH, supported by either isocitrate or succinate as a source of reducing equivalents, and present at nearly the same levels of activity. The 19- and 11.beta.-OHase activity in other subcellular fractions appeared to be of mitochondrial origin. The cytosol contained a C-17 oxidoreductase catalyzing the interconversion between A and T in the presence of the appropriate NADP(H) cofactor. The 19-OHase of the gerbil adrenal gland [apparently] is primarily a mitochondrial enzyme. The localization and activities of both the 19- and 11.beta.-OHases account for the relative amounts of the major corticosteroids found in the blood of the gerbil.