In enzymology, a 3-β(or 20-α)-hydroxysteroid dehydrogenase () is an enzyme that catalyzes the chemical reaction
5α-androstan-3β,17β-diol + NADP+ 17β-hydroxy-5α-androstan-3-one + NADPH + H+
This enzyme possesses the combined activities of the 3-β-hydroxysteroid dehydrogenase/Δ-5-4 isomerase and 20-α-hydroxysteroid dehydrogenase enzymes.
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