Enzymatic synthesis of a $beta;--galactopyranosyl cyclic tetrasaccharide by $beta;-galactosidases

Abstract

Graphic The galactosyl transfer reaction to cyclo -{→ 6)-α- d -Glc p -(1 → 3)-α- d -Glc p -(1 → 6)-α- d -Glc p -(1 → 3)-α- d -Glc p -(1 →} (CTS) was examined using lactose as a donor and β-galactosidases from Aspergillus oryzae and Bacillus circulans. The A. oryzae β-galactosidase produced three galactosyl derivatives of CTS. The main galactosyl derivative produced by the A. oryzae enzyme was identified as 6- O -β- d -galactopyranosyl-CTS, cyclo -{→ 6)-α- d -Glc p -(1 → 3)-[β- d -Gal p -(1 → 6)]-α- d -Glc p -(1 → 6)-α- d -Glc p -(1 → 3)-α- d -Glc p -(1 →}. The B. circulans β-galactosidase also synthesized three galactosyl-transfer products to CTS. The structure of main transgalactosylation product was 3- O -β- d -galactopyranosyl-CTS, cyclo -{→ 6)-α- d -Glc p -(1 → 3)-α- d -Glc p -(1 → 6)-[β- d -Gal p -(1 → 3)]-α- d -Glc p -(1 → 3)-α- d -Glc p -(1 →}. These results showed that β-galactosidase transferred galactose directly to the ring glucose residue of CTS.