In enzymology, a cholest-5-ene-3β,7α-diol 3β-dehydrogenase (EC 1.1.1.181) is an enzyme that catalyzes the chemical reaction^[1]

cholest-5-ene-3β,7α-diol + NAD⁺ ${\displaystyle \rightleftharpoons }$ 7α-hydroxycholest-4-en-3-one + NADH + H⁺

Thus, the two substrates of this enzyme are cholest-5-ene-3β,7α-diol and NAD⁺, whereas its 3 products are 7α-hydroxycholest-4-en-3-one, NADH, and H⁺.

The systematic name of this enzyme class is cholest-5-ene-3β,7α-diol:NAD⁺ 3-oxidoreductase. This enzyme is also called 3β-hydroxy-Δ5-C27-steroid oxidoreductase. The human version of this enzyme is known as hydroxy-Δ-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 7 or HSD3B7 which is encoded by the HSD3B7 gene.^[2][3]

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD⁺ or NADP⁺ as acceptor. This enzyme is involved in the initial stages of the synthesis of bile acids from cholesterol and a member of the short-chain dehydrogenase/reductase superfamily. This enzyme is a membrane-associated endoplasmic reticulum protein which is active against 7-alpha hydrosylated sterol substrates.^[4]

Mutations in the HSD3B7 gene are associated with a congenital bile acid synthesis defect which leads to neonatal cholestasis, a form of progressive liver disease.^[4]

• 3-beta-HSD