The effect of adenosine 3',5'-cyclic-monophosphoric acid on the 17β-hydroxysteroid dehydrogenase of rat testis

The effect of adenosine 3',5'-cyclic-monophosphoric acid on the conversion of 4-androstene-3,17 dione (4-androstenedione) to 17β-hydroxy-4-androsten-3-one (testosterone) catalyzed by a 17β-hydroxysteroid dehydrogenase (EC 1.1.1.64) was studied. Mitochondrial and microsomal fractions isolated from rat testicular tissue served as the source of enzyme employed in the present experiments. The conversion of testosterone to 4-androstenedione, in the presence of NAD⁺, was inhibited by adenosine 3',5'-cyclic-monophosphoric acid. However, the cyclic nucleotide had no effect on this conversion when NADP⁺ was used as co-factor. Furthermore, the transformation of 4-androstenedione to testosterone in the presence of NADPH was not influenced by the cyclic nucleotide. The inhibitory effect of the cyclic nucleotide on the NAD⁺ dependent conversion of testosterone to 4-androstenedione was counteracted by increasing the concentration of exogenous NAD⁺. The inhibition of NAD⁺ dependent 17β-hydroxysteroid dehydrogenase by the cyclic nucleotide confirms early reports on the inhibitory effect of this nucleotide on the NAD⁺ dependent 5-ene-3β-hydroxysteroid dehydrogenase (EC 1.1.1.51). The results also indicate that steroid dehydrogenase which utilizes NADP⁺ for the transfer of electrons is not influenced by adenosine 3',5'-cyclic-monophosphoric acid.