Abstract
The adrenal gland of the Mongolian gerbil produces nearly equal amounts of 19-hydroxy- and of 11β-hydroxycorticosteroids (Oliver and Peron, Steroids
4, 351 (1964)). The intracellular location of the 19-hydroxylase (OHase) was studied by determining the activities of both the 19- and 11β-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 two products detected were 19-hydroxy A and 11β-hydroxy A; the two were formed at virtually identical rates. With subcellular fractions, the capacity for 19-hydroxylation coincided with that for 11β-hydroxylation; the highest activities were in adrenal mitochondria. For adrenal mitochondria the two hydroxylation reactions were (1) enhanced by the addition of Ca2+ to incubations containing NADPH, (2) supported by either isocitrate or succinate as a source of reducing equivalents, and (3) present at nearly the same levels of activity. The 19- and 11β-OHase activity in other subcellular fractions appeared to be of mitochondrial origin. The cytosol was found to contain a C-17 oxidoreductase catalyzing the interconversion between A and T in the presence of the appropriate NADP(H) cofactor. It was concluded that the 19-OHase of the gerbil adrenal gland is primarily a mitochondrial enzyme. The localization and activities of both the 19- and 11β-OHases account for the relative amounts of the major corticosteroids found in the blood of the gerbil.
