Pregnenolone-binding components in the porcine adrenal gland

The object of this study was to determine whether binding components for pregnenolone, analogous to those described in the adrenal cortex of guinea pigs and rats, were present in the porcine adrenal. A binding component for pregnenolone in the cytosolic fraction of porcine adrenal was demonstrated by sucrose density gradient centrifugation. It banded maximally at 9.6% sucrose (w/w) compared to 12.2% and 12.4% sucrose (w/w) for the plasma-binding component and serum albumin, respectively. At a pregnenolone concentration of 1 X 10(-5) M, specific cytosolic binding of 1 X 10(-8) M [3H]pregnenolone was decreased by 42%. The fractions from sucrose gradients which bound pregnenolone maximally contained 3 beta-hydroxysteroid dehydrogenase-isomerase. The cytosolic supernatant of porcine adrenal gland was resolved by chromatography on hydroxyapatite into eleven fractions, four of which bound added pregnenolone and three of which displayed enzymatic activity. Electrophoretic analysis of the enzymatically active fractions in polyacrylamide gel showed that two of them were of heterogeneous composition, whereas the third, most enzymatically active, fraction consisted principally of one band of high molecular weight.