Xanthomonas maltophilia CBS 897.97 as a source of new 7β- and 7α-hydroxysteroid dehydrogenases and cholylglycine hydrolase:: Improved biotransformations of bile acids

The paper reports the partial purification and characterization of the 7 beta- and 7 alpha-hydroxysteroid dehydrogenases (HSDH) and cholylglycine hydrolase (CGH), isolated from Xanthomonas maltophilia CBS 897.97. The activity of 7 beta-HSDH and 7 alpha-HSDH in the reduction of the 7-keto bile acids is determined. The affinity of 7 beta-HSDH for bile acids is confirmed by the reduction, on analytical scale, to the corresponding 7 beta-OH derivatives. A crude mixture of 7 alpha- and 7 beta-HSDH, in soluble or immobilized form, is employed in the synthesis, on preparative scale, of ursocholic and ursodeoxycholic acids starting from the corresponding 7 alpha-derivatives. On the other hand, a partially purified 7 beta-HSDH in a double enzyme system, where the couple formate/formate dehydrogenase allows the cofactor recycle, affords 6 alpha-fluoro-3 alpha, 7 beta-dihydroxy-5 beta-cholan-24-oic acid (6-FUDCA) by reduction of the corresponding 7-keto derivative. This compound is not obtainable by microbiological route. The efficient and mild hydrolysis of glycinates and taurinates of bile acids with CGH is also reported. Very promising results are also obtained with bile acid containing raw materials. (c) 2005 Elsevier Inc. All rights reserved.