7alpha-hydroxysteroid dehydrogenase involved in the metabolism of bile acids in the gut. Catalyzes the NAD(+)-dependent oxidation of the 7alpha-hydroxy group of 7alpha-hydroxysteroids, such as cholate, chenodeoxycholate, taurochenodeoxycholate, glycochenodeoxycholate, taurocholate and glycocholate, to the corresponding 7-oxosteroids (PubMed:14756531). Since it is also able to catalyze the reduction of nonsteroidal carbonyl compounds such as various benzaldehyde analogs to their corresponding benzyl alcohols, this enzyme may also function in the detoxification of xenobiotics containing carbonyl groups in the large intestine (PubMed:21600233). cholate + NAD(+) = 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholanate + H(+) + NADH chenodeoxycholate + NAD(+) = 7-oxolithocholate + H(+) + NADH NAD(+) + taurochenodeoxycholate = 7-oxotaurolithocholate + H(+) + NADH glycochenodeoxycholate + NAD(+) = 7-oxoglycolithocholate + H(+) + NADH NAD(+) + taurocholate = 7-oxo-taurodeoxycholate + H(+) + NADH glycocholate + NAD(+) = 7-oxo-glycodeoxycholate + H(+) + NADH an aromatic primary alcohol + NAD(+) = an aromatic aldehyde + H(+) + NADH benzyl alcohol + NAD(+) = benzaldehyde + H(+) + NADH 4-cyanobenzyl alcohol + NAD(+) = 4-cyanobenzaldehyde + H(+) + NADH 4-acetoxybenzyl alcohol + NAD(+) = 4-acetoxybenzaldehyde + H(+) + NADH 4-(trifluoromethyl)benzyl alcohol + NAD(+) = 4-(trifluoromethyl)benzaldehyde + H(+) + NADH Optimum pH is pH 8.5 (NAD reduction, bile acid oxidation) and 6.5 (NADH oxidation, bile acid reduction). Is relatively thermostable, retaining 95% of initial activity after 1 hour at 65 degrees Celsius. Homotetramer. Up-regulated by cholate and after the transition of the cells from log phase to stationary growth phase. Belongs to the short-chain dehydrogenases/reductases (SDR) family.