Regioselectivity of the enzymatic transgalactosidation of D- and L-xylose catalysed by beta-galactosidases

The regioselectivity of enzymatic transgalactosidation depends on the source of the beta-galactosidase used. When the galactosyl acceptor only contains secondary hydroxyl groups, e.g., D- or L-xylose, it is possible to find an enzyme that catalyses preferentially the synthesis of any of the three regioisomers 4-, 3- and 2-O-beta-D-galactopyranosyl-D-xylose (1, 2 and 3, respectively) or 4-, 3- and 2-O-beta-D-galactopyranosyl-L-xylose (4, 5 and 6, respectively). Enriched mixtures in 1, 2 or 3 were obtained using beta-galactosidases from Escherichia coli, bovine testes or Aspergillus oryzae, respectively, by transgalactosidation reaction of O-nitrophenyl-beta-D-galactopyranoside and D-xylose, and enriched mixtures in 4, 5 or 6 were obtained in a similar way using beta-galactosidases from Aspergillus oryzae, lamb small-intestine (intestinal lactase-phloridzin hydrolase) or Saccharomyces fragilis, respectively, using L-xylose as acceptor.