Steroidogenic potential of lyophilized mitochondria from bovine adrenocortical tissue

When incubated with [3H]cholesterol, a bovine adrenocortical mitochondrial pellet obtained by centrifugation at 12,000 x g yielded, as expected, only the C21O2 metabolites progesterone and pregnenolone. However, the steroidogenic potential of the 12,000 x g pellet fraction was augmented significantly by lyophilization. After lyophilization, the 12,000 x g pellet converted the sterol into C19 androgens and corticosteroids, in addition to C21O2 pregnane derivatives. Leaching the lyophilized mitochondrial fraction with either hexane or acetone increased substantially the yields of the metabolites. It did not change qualitatively the array of metabolites formed during in vitro incubation, but 5 alpha-reductase activity was unmasked by the washings, particularly with acetone. Thus, the fraction sedimented at 12,000 x g contains the complete complement of steroidogenic enzymes required for the biosynthesis of the aforementioned adrenal hormones. These results cast doubt upon the widely held belief that the various enzymes required for adrenocortical steroidogenesis are distributed between two different subcellular compartments, the mitochondrion and the endoplasmic reticulum.