3-oxo-5alpha-steroid 4-dehydrogenase

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In enzymology, a 3-oxo-5alpha-steroid 4-dehydrogenase (EC 1.3.99.5) is an enzyme that catalyzes the chemical reaction

a 3-oxo-5alpha-steroid + acceptor $\rightleftharpoons$ a 3-oxo-Delta₄-steroid + reduced acceptor

Thus, the two substrates of this enzyme are 3-oxo-5alpha-steroid and acceptor, whereas its two products are 3-oxo-Delta4-steroid and reduced acceptor.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with other acceptors. The systematic name of this enzyme class is 3-oxo-5alpha-steroid:acceptor Delta4-oxidoreductase. Other names in common use include steroid 5alpha-reductase, 3-oxosteroid Delta4-dehydrogenase, 3-oxo-5alpha-steroid Delta4-dehydrogenase, steroid Delta4-5alpha-reductase, Delta4-3-keto steroid 5alpha-reductase, Delta4-3-oxo steroid reductase, Delta4-3-ketosteroid5alpha-oxidoreductase, Delta4-3-oxosteroid-5alpha-reductase, 3-keto-Delta4-steroid-5alpha-reductase, 5alpha-reductase, testosterone 5alpha-reductase, 4-ene-3-ketosteroid-5alpha-oxidoreductase, Delta4-5alpha-dehydrogenase, and 3-oxo-5alpha-steroid:(acceptor) Delta4-oxidoreductase. This enzyme participates in 3 metabolic pathways: bile acid biosynthesis, androgen and estrogen metabolism, and prostate cancer.