Characterisation of the in vitro products of potato starch branching enzymes I and II

An enzyme substrate obtained by ethanol fractionation of linear dextrins was branched by potato starch branching enzymes (SBE). During the branching process, samples were withdrawn from the incubation mixture and the chain length distributions were analysed by high performance anion exchange chromatography (HPAEC). The relative composition of chains with a degree of polymerisation of 9–35 was essentially constant throughout the branching process for both SBEI and SBEII. This showed that the change in size and structure of the substrate during the branching reaction did not considerably affect the patterns of chains produced by the enzymes. Chain length patterns as well as branching rates were different for the two SBE isoforms, supporting the theory that they have different roles in amylopectin synthesis. Despite the differences in chain length profiles, the degree of branching was found to be 3.7% for both SBE products when analysed by NMR. Using proton 2D-NMR, the structural differences between intact branching products and their β-limit dextrins were determined.