an isomaltosyl residue were synthesized by alpha-glucosidase fromAspergillusniger by using maltotetraose as a glucosyl donor and trehalose as the acceptor. The one trisaccharide and two tetrasaccharides formed were isolated by successive column chromatography. The results of an enzymatic digestion, methylation analysis, and 13C-NMR studies indicated that these oligosaccharides were alpha-isomaltosyl