7alpha-hydroxysteroid dehydrogenase involved in the metabolism of bile acids. Catalyzes the NAD(+)-dependent oxidation of the 7alpha-hydroxy group of 7alpha-hydroxysteroids, such as the major human bile acids cholate and chenodeoxycholate, to the corresponding 7-oxosteroids. To a lesser extent, can also act on taurochenodeoxycholate, taurocholate and glycocholate (PubMed:2007545). Can also use glycochenodeoxycholate as substrate (PubMed:8672472). Is not able to use NADP(+) instead of NAD(+) as the electron acceptor (PubMed:2007545). cholate + NAD(+) = 3alpha,12alpha-dihydroxy-7-oxo-5beta-cholanate + H(+) + NADH chenodeoxycholate + NAD(+) = 7-oxolithocholate + H(+) + NADH NAD(+) + taurochenodeoxycholate = 7-oxotaurolithocholate + H(+) + NADH NAD(+) + taurocholate = 7-oxo-taurodeoxycholate + H(+) + NADH glycocholate + NAD(+) = 7-oxo-glycodeoxycholate + H(+) + NADH glycochenodeoxycholate + NAD(+) = 7-oxoglycolithocholate + H(+) + NADH Inhibited by N-bromosuccinimide, diethyl pyrocarbonate, and some metal ions such as Co(2+), Fe(2+) and Cu(2+). kcat is 3798 sec(-1) with cholate as substrate (PubMed:2007545). kcat is 491 sec(-1) with chenodeoxycholate as substrate (PubMed:2007545). kcat is 206 sec(-1) with taurochenodeoxycholate as substrate (PubMed:2007545). kcat is 188 sec(-1) with taurocholate as substrate (PubMed:2007545). kcat is 25 sec(-1) with glycocholate as substrate (PubMed:2007545). kcat is 151 sec(-1) with cholate as substrate (PubMed:9722677). Optimum pH is 8.5 (PubMed:2007545). The enzyme is stable between pH 8 and 9 (PubMed:2007545). Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family.