Monitoring the hydrolysis and transglycosylation activity of α-glucosidase from Aspergillus niger by nuclear magnetic resonance spectroscopy and mass spectrometry

α-Glucosidase from Aspergillus niger is an enzyme that catalyzes hydrolysis of α-1,4 linkages and transglucosylation to form α-1,6 linkages. In this study, an analytical method of oligosaccharides by nuclear magnetic resonance (NMR) was used to provide quantitative estimation of the fractions of each sugar unit and was applied to characterize the α-glucosidase reaction. Our data indicated that α-glucosidase reacts with the nonreducing end of oligosaccharides to form an α-1,6 linkage, and then a sugar unit with two α-1,6 linkages is gradually produced. Data from mass spectrometry suggested that the sugar unit with two α-1,6 linkages originates mainly from a 3mer and/or 4mer when oligosaccharides are used as substrates.