Abstract
Starch digestion requires two luminal enzymes, salivary and pancreatic alpha‐amylase (AMY), and four small intestinal mucosal enzyme activities from the N‐ and C‐terminals of maltase‐glucoamylase (MGAM) and sucrose‐isomaltase (SI) complexes. AMY is not a requirement for starch digestion to glucose but dramatically amplifies α‐glucogenesis by producing α‐limit dextrins (LDx) as favored substrates for the mucosal enzymes.Aimto study substrate specificity of α‐glucogenesis by four recombinant MGAM and SI subunits.MethodsRecombinant α‐glucosidase domains were produced in drosophila (N‐) or baculovirus (C‐) cell lines and purified by histags. LDx was produced with AMY from normal maize and three mutant cultivars with different amylopectin structures: normal, waxy, ae waxy and du waxy. Glucose released in vitro was measured by GOPOD.ResultsN‐MGAM subunit releases glucose from shortest linear oligomers while the other three subunits digest longer chains or branched molecules.ConclusionsThis is the first time that the individual α‐glucogenic activities of all four mucosal enzyme subunits have been tested. The individual α‐glucosidase subunits had different activities for each cultivar LDx substrate and selective affinities for LDx from different cultivars. Combinations of α‐glucosidase subunits thus provide a broader spectrum of α‐glucogenic activities from structurally varied starch LDx.
Published Version
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