Study of the Regioselectivity in the Transglycosylation to D-Galactose Derivatives Using .BETA.-Galactosidases of Various Origins

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Although a recombinant β-1,3-galactosidase from Bacillus circulans has been recognized to catalyze a regioselective transglycosylation to give β-(1→3)-linked oligosaccharides, β-D-Galp-(1→6)-D-Gal derivatives were recently reported to be synthesized predominantly when D-galactose derivatives were used as acceptors. In the present study, the relation between the regioselectivity in the transglycosylation reaction and the hydrolysis specificity of the β-1,3-galactosidase was examined. Although β-D-Galp-(1→3)-D-GalNAc was hy-drolyzed much faster than β-D-Galp-(1→6)-D-GalNAc, β-D-Galp-(1→3)-β-D-Galp-OMe was hydrolyzed slower than β-D-Galp-(1→6)-β-D-Galp-OMe. This fact indicated preferential synthesis of β-D-Galp-(1→6)-β-D-Galp-OMe by transglycosylation. In the transglycosylation using other β-galactosidases of different origins such as from B. circulans, bovine testes, and E. coli, moderate regioselectivity was observed in reactions using D-galactose as an acceptor. The unexpected regioselectivity in the transglycosylation to D-galactose was concluded to be a result only found in the reaction using the β-1,3-galactosidase from Bacillus circulans, and could be attributed to irregular specificity in the hydrolysis reaction.
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