In enzymology, 12alpha-hydroxysteroid dehydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are the bile acid, cholic acid, and oxidised nicotinamide adenine dinucleotide phosphate (NADP<sup>+</sup>). Its products are 12-ketochenodeoxycholic acid, reduced NADPH, and a proton.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD<sup>+</sup> or NADP<sup>+</sup> as acceptor. The systematic name of this enzyme class is 12alpha-hydroxysteroid:NADP<sup>+</sup> 12-oxidoreductase. Other names in common use include 12alpha-hydroxy steroid dehydrogenase, 12alpha-hydroxy steroid dehydrogenase, NAD<sup>+</sup>-dependent 12alpha-hydroxysteroid dehydrogenase, and NADP<sup>+</sup>-12alpha-hydroxysteroid dehydrogenase. This enzyme is involved in a metabolic pathway that degrades bile acids into cholesterol.