7beta-hydroxysteroid dehydrogenase that catalyzes the reduction of the 7-oxo group of 7-oxo-lithocholate (7-oxo-LCA), to yield ursodeoxycholate (UDCA). As R.gnavus is a common core bacterium of the human gut microbiota, this enzyme contributes to the formation of UDCA in the human colon. UDCA is regarded as a chemopreventive beneficial secondary bile acid due to its low hydrophobicity; it protects hepatocytes and bile duct epithelial cells against necrosis and apoptosis induced by more hydrophobic secondary bile acids like deoxycholate (DCA). This enzyme is also able to catalyze the reverse reaction in vitro, i.e. the oxidation of the 7beta-hydroxy group of UDCA to 7-oxo-LCA, but much less efficiently than the reduction reaction, and this oxidation reaction is not observed in vivo. It is specific for NADPH/NADP(+) as the electron acceptor/donor since the activity observed with NADH/NAD(+) is less than 0.5% of that assayed using NADPH/NADP(+) in both directions. a 7beta-hydroxysteroid + NADP(+) = a 7-oxosteroid + H(+) + NADPH 7-oxolithocholate + H(+) + NADPH = NADP(+) + ursodeoxycholate kcat is 700 min(-1) for the reduction of 7-oxolithocholate (7-oxo-LCA) (at pH 6 and 37 degrees Celsius). kcat is 326 min(-1) for the oxidation of ursodeoxycholate (UDCA) (at pH 10 and 37 degrees Celsius). Optimum pH is 6 and 10 for the reduction and oxidation reactions, respectively. Optimum temperature is 37 degrees Celsius for the reduction reaction. The enzyme appears mostly inactivated at 60 degrees Celsius. Belongs to the short-chain dehydrogenases/reductases (SDR) family.