Conversion of a C-20-deoxy-C21, steroid, 5-pregnen-3beta-ol, into testosterone by rat testicular microsomes

5-[7ALPHA-3H] Pregnen-3beta-ol, a C-20-deoxy analog of pregnenolone, was synthesized and tested as a substrate for the enzyme system occurring in testes that cleaves the side chain of C21 steroids between C-17 and C-20. This C-20-deoxy C21 steroid was incubated with a microsomal preparation obtained from rat testis and was converted into testosterone in 5% yield. Another C-20-deoxy analog of pregnenolone, 5,20-pregnadien-3beta-ol, was not converted into testosterone by this enzyme system. The significance of this finding for the natural processes by which pregnenolone is converted by the same subcellular fraction into the male sex hormone is examined in the light of the hypothesis that intermediates involved in steroidogenesis are transient, reactive complexes of the appropriate reactants (steroids, oxygen, etc.) with specific enzymes.