Activation of Solubilized Steroid-Transforming Enzymes of Adrenal Microsomal Origin by Serum Proteins

Abstract

The reactions which result in the conversion of pregnenolone to progesterone and of progesterone to deoxycorticosterone in undisrupted microsomal preparations from rat adrenal glands were stimulated by homologous serum. The active materials were shown to be firmly associated with serum proteins. The dialysable fraction of serum was either without effect on these transformations or was inhibitory. The enzyme systems involved were partially solubilized by exposure of the microsomal preparation to prolonged sonic treatment or to 1% Triton N-101. After either treatment, 35-40% of the original specific activity of the steroid 21-hydroxylase system responsible for the conversion of progesterone to deoxycorticosterone was found in the supernatant fraction after high-speed centrifuga-J Reprint requests to S. R. hydroxysteroid dehydrogenase activity, but did not activate 5-ene-3oxosteroid isomerase in the microsomal fraction. This finding suggested that activation of 5-ene-3/?-hydroxysteroid dehydrogenase was responsible for stimulation of progesterone synthesis from pregnenolone. The results indicate that the protein-bound factor in rat serum which was capable of stimulating the conversion of progesterone to deoxycorticosterone in microsomal preparations from rat adrenal glands was different from that which activates the conversion of pregnenolone to progesterone. Moreover, these diverse factors appeared to act by different mechanisms.-60°C. The frozen

Expression of ACTH-induced corticosteroid biosynthesis in newborn rat adrenocortical cells cultured in serum-free and carrier protein-free medium containing a cholesterol-?-cyclodextrin complex

“…In SFM-S containing cholesterol albumin, however, the 21-hydroxylated steroid biosynthetic pathway was low, corresponding to a ratio of 0.5, when compared to the 20a-reduced steroid metabolic route, even if the total steroid production was slightly higher. Other reports using subcellular systems have described interactions between albumin and steroid producing enzymes showing an activating effect of this protein on the 3/3-hydroxysteroid dehydrogenase (Hamilton et al, 1972;Bertolino et al, 1979). It may be hypothesized that, in our adrenal cell cultures, albumin itself or impurities of albumin will interact with the steroid metabolizing enzymes by increasing the activity of 20a-steroid dehydrogenase and/or decreasing that of 21-steroid hydroxylase ( Table 1).…”

5-Ene-3β-Hydroxysteroid DEHYDROGENASE OF HUMAN AND BOVINE ADRENOCORTICAL ENDOPLASMIC RETICULUM: SOLUBILIZATION AND FRACTIONATION

“…Previous authors attempting such an investigation have reported the disruption of microsomes into smaller, heterogeneously sized particles, often remaining in suspension after high-speed centrifugation, in which 5-ene-3/?-hydroxysteroid dehydrogenase or 5-en-4-en-3-oxosteroid isomerase activities were observed. Such results were obtained by Ewald, Werbin & Chaikoff (1964), Neville & Engel (1968) and Hamilton, McCune & Roberts (1972) who attempted solubilization with various detergents, Cheatum et al (1967) using sonication, andGeynet, Gallay &Alfsen (1972), who exposed their preparations to high concentrations of divalent cations. It is possible that some of these authors achieved solubilization of the enzymes, only to be obscured by the presence of paniculate matter which possessed active steroidogenic enzymes.…”

Enzyme-Like Activities Associated With Albumin

“…Hamid et al (49) reported that a protamine stimulated trigylceride hydrolyzing enzyme from rat ventricle was stimulated two-fold by albumin, but no explanation of the effect was presented and other proteins were not examined for similar effects. Hamilton et al (51) reported that the microsomal enzyme from rat adrenal which catalyzes the conversion of pregnenolone to progesterone could be stimulated by a factor of about 40-60% by a variety of animal serum albumins and lactalbumin. Hamilton et al (51) reported that the microsomal enzyme from rat adrenal which catalyzes the conversion of pregnenolone to progesterone could be stimulated by a factor of about 40-60% by a variety of animal serum albumins and lactalbumin.…”