[Specificity of 3 alpha, 20 beta-hydroxysteroid: nad+ -oxidoreductase (author's transl)].

The enzyme 3 alpha, 20 beta-hydroxysteroid:NAD+ oxidoreductase (EC 1.1.1.53) catalyses the stoichiometric reduction of 20-oxo groups of C-21 steroids by NADH, and the non-stoichiometric oxidation of 3 alpha-hydroxy groups of 5 alpha-androstane derivatives by NAD. The activity of the enzyme towards the most important C-18, C-19 and C-21 steroids of human urine was tested in the presence of NAD and NADH. The rate of reduction of 20-oxo steroids is influenced by substituents at various positions of the steroid skeleton. These studies are intended as the basis of an eventual clinical chemical application.