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-Glc p-(1→6)-α- d-Glc p-(1→} 2 ( cGlc 4). 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 cGlc 4. The attachment of a nonreducing α- d-galactopyranosyl residue to the cGlc 4 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.