Influence of Transcortin and Albumin on the Rate of Reduction of Progesterone by Human Placental 20α-Hydroxysteroid Dehydrogenase

Abstract

Purified human placental 20α-hydroxysteroid dehydrogenase was incubated with progesterone-4-¹⁴C in the presence or absence of purified transcortin or albumin. Transcortin inhibited the conversion of progesterone to 20α-hydroxypregn-4-en-3-one. As the progesterone concentration was increased, the transcortin inhibition decreased. The trans-cortin inhibition of the enzymatic conversion correlated directly with the binding of progesterone by transcortin. In the absence of trans-cortin, cortisol had no effect on the conversion to 20α-hydroxypregn-4-en-3-one, but cortisol did reduce the transcortin inhibition of the pro-gesterone-4-14C metabolism. The data are interpreted to indicate that progesterone bound to transcortin is not available for the enzymatic reaction. Relatively high concentrations (2–64 mg/3 ml) of human albumin decreased the enzymatic 20α-reduction of progesterone-4-¹⁴C while low concentrations (0.1−1.0 mg/3 ml) stimulated this reaction. (Endocrinology84: 1152, 1969)