Enzymic α-galactosylation of a cyclic glucotetrasaccharide derived from alternan

Abstract

Alternanase catalyzes the hydrolysis of alternan, an α-(1 → 3)-α-(1 → 6)-D-glucan produced by Leuconostoc mesenteroides, resulting in the formation of a cyclic tetramer cyclo { → 3)-α-D-Glcp-(1 → 6)-α-D-Glcp-(1 → }2 (cGlc4). Two α-galactosidases, one from coffee bean and the other produced by a fungus, currently described as Thermomyces lanuginosus, were found to catalyze an efficient 6-O-α-D-galactopyranosylation of cGlc4. The attachment of a nonreducing α-D-galactopyranosyl residue to the cGlc4 molecule opens new possibilities for future applications of the cyclic tetramer, since the D-galactopyranosyl residue can be easily modified by D-galactose oxidase to introduce a reactive aldehyde group. The results also extend our knowledge about the synthetic potential of T. lanuginosus α-galactosidase. © 2001 Elsevier Science Ltd.