Article Molecular and enzymatic properties of 7α-hydroxysteroid dehydrogenase from Pseudomonas sp. B-0831

A novel 7α-hydroxysteroid dehydrogenase (7α-HSD) was purified from Pseudomonas sp. B-0831. The molecular weight of the purified enzyme was 25 k on SDS-PAGE and 108 k on gel filtration analysis, suggesting that the enzyme exists as a tetramer of an identical subunit, similar to those of 7α-HSD from E. coli HB101 and Eubacterium sp. VPI 12708. 7α-HSD from P. sp. B-0831 showed high NAD+-dependence and was able to catalyze the oxido-reduction of 7α-hydroxy bile acids including glycine and taurine conjugates. The Km value for cholic acid was determined to be 0.25 mM, which is similar to that for chenodeoxycholic acid and is about four times smaller than those for the conjugates of cholic acid. The kcat values for the conjugates were determined to be about 60-70 % of that for free cholic acid. In addition to NAD+, 7α-HSD from P. sp. B-0831 can utilize thio-NAD+ to the same extent