Enzymic α-galactosylation of a cyclic glucotetrasaccharide derived from alternan

Alternanase catalyzes the hydrolysis of alternan, an alpha-(1 --> 3)-alpha-(1 --> 6)-D-glucan produced by Leuconostoc mesenteroides, resulting in the formation of a cyclic tetramer cycle{ --> 3)-alpha -D-Glcp-(1 --> 6)-alpha -D-Glcp-(1 -->}(2) (cGlc(4)). Two alpha -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-alpha -D-galactopyranosylation of cGlc(4). The attachment of a nonreducing alpha -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 alpha -galactosidase. (C) 2001 Elsevier Science Ltd. All rights reserved.