The conversion of progesterone into 5 alpha-pregnane-3,20-dione, 3 beta-hydroxy-5 alpha-pregnan-20-one, and its fatty acid esters by preparations of bovine corpora lutea.

Homogenates obtained from bovine corpora luteal tissue were found to catalyze the synthesis of 3 beta-hydroxy-5 alpha-pregnan-20-one (allopregnanolone) from progesterone but not from pregnenolone. The major metabolites of progesterone included allopregnanolone, 5 alpha-pregnane-3,20-dione, and fatty acid esters of allopregnanolone. Incubation with labeled pregnenolone resulted in the formation of pregnenolone esters; however, neither allopregnanolone nor esterified derivatives of it were detected. The esterifying enzyme(s) leading to the formation of allopregnanolone esters was associated primarily with the microsome-enriched subcellular fraction and was stimulated by the addition of ATP and coenzyme A. With these added cofactors, the pH optimum was 6.0-6.5. The rate of steroid ester formation was enhanced by the addition to the homogenate fraction of oleic acid, which was incorporated into the steroid ester fraction. Thus, enzymatic activity, with characteristics similar to either cholesteryl ester hydrolase (EC 3.1.1.13) or acyl cholesterol acyltransferase (EC 2.3.1.26), catalyzed the esterification of allopregnanolone. The data suggest that the allopregnanolone esters found in vivo are derived from progesterone rather than from pregnenolone.