Stereochemistry of Hydrogen Transfer from Pyridine Nucleotides Catalyzed by Δ⁴‐3‐Oxosteroid 5β‐Reductase and 3α‐Hydroxysteroid Dehydrogenase from Rat Liver

The stereochemistry of hydrogen transfer from NADPH in the conversion of Δ 4 ‐3‐oxosteroids into 3‐oxo‐5β‐steroids and from NADH and NADPH in the conversion of 3‐oxo‐5β‐and 3‐oxo‐5α‐steroids into 3α‐hydroxysteroids, catalyzed by rat liver Δ 4 ‐3‐oxosteroid 5β‐reductase and 3α‐hydroxysteroid dehydrogenase, respectively, was studied with C 19 ‐, C 21 ‐, C 24 ‐, and C 27 ‐steroids. In all cases, the hydrogen transferred from the pyridine nucleotides was the 4A‐hydrogen.