Enzymic α-galactosylation of a cyclic glucotetrasaccharide derived from alternan Original Research Article

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.