Characterization and Monitoring of Isomalto/Malto-Polysaccharide Formation by Different 4,6-α-Glucanotransferases

GtfB type I enzymes, a subfamily of 4,6-α-glucanotransferases, are enzymes which convert starch into isomalto/malto-polysaccharides (IMMPs) by synthesizing α-1,6-linked chains. The structure of IMMPs highly depends on the enzyme and the substrate used. In this study, the IMMP formation of eight GtfB type I enzymes was investigated in detail by using different substrates and conditions. ¹H NMR spectroscopy was used to analyze the structural composition (including the portion of released glucose) and revealed little impact of pH and temperature on the product composition for the investigated enzymes. However, enzymatic fingerprinting analysis revealed enzyme-dependent differences in the length distribution of the 1,6-linked sections of the IMMPs. A detailed reaction monitoring by HPAEC-PAD and NMR spectroscopy showed that larger oligosaccharides are initially used for IMMP synthesis and that branched malto-oligosaccharides are also converted. Overall, detailed information on the reaction time course and the structural composition of the products were obtained.