title: Starch source influences dietary glucose generation at the mucosal α-glucosidase level.
abstract: The quality of starch digestion, related to the rate and extent of release of dietary glucose, is associated with glycemia-related problems such as diabetes and other metabolic syndrome conditions. Here, we found that the rate of glucose generation from starch is unexpectedly associated with mucosal α-glucosidases and not just α-amylase. This understanding could lead to a new approach to regulate the glycemic response and glucose-related physiologic responses in the human body. There are six digestive enzymes for starch: salivary and pancreatic α-amylases and four mucosal α-glucosidases, including N- and C-terminal subunits of both maltase-glucoamylase and sucrase-isomaltase. Only the mucosal α-glucosidases provide the final hydrolytic activities to produce substantial free glucose. We report here the unique and shared roles of the individual α-glucosidases for α-glucans persisting after starch is extensively hydrolyzed by α-amylase (to produce α-limit dextrins (α-LDx)). All four α-glucosidases share digestion of linear regions of α-LDx, and three can hydrolyze branched fractions. The α-LDx, which were derived from different maize cultivars, were not all equally digested, revealing that the starch source influences glucose generation at the mucosal α-glucosidase level. We further discovered a fraction of α-LDx that was resistant to the extensive digestion by the mucosal α-glucosidases. Our study further challenges the conventional view that α-amylase is the only rate-determining enzyme involved in starch digestion and better defines the roles of individual and collective mucosal α-glucosidases. Strategies to control the rate of glucogenesis at the mucosal level could lead to regulation of the glycemic response and improved glucose management in the human body.
authors.affiliation: Whistler Center for Carbohydrate Research and Department of Food Science, Purdue University, West Lafayette, Indiana 47907-2009, USA. amylin@purdue.edu
authors.forename: Amy Hui-Mei
authors.initials: AH
authors.lastname: Lin
authors.forename: Byung-Hoo
authors.initials: BH
authors.lastname: Lee
authors.forename: Buford L
authors.initials: BL
authors.lastname: Nichols
authors.forename: Roberto
authors.initials: R
authors.lastname: Quezada-Calvillo
authors.forename: David R
authors.initials: DR
authors.lastname: Rose
authors.forename: Hassan Y
authors.initials: HY
authors.lastname: Naim
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Hamaker
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism; D003912:Dextrins / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D051379:Mice; D008970:Molecular Weight; D009092:Mucous Membrane / Q000201:enzymology*; D021122:Protein Subunits / Q000737:chemistry; D013213:Starch / Q000737:chemistry; D003313:Zea mays / Q000737:chemistry; D000516:alpha-Amylases / Q000737:chemistry; D000520:alpha-Glucosidases / Q000737:chemistry*
chemical_list: D003912:Dextrins; D021122:Protein Subunits; D013213:Starch; D000516:alpha-Amylases; D000520:alpha-Glucosidases; D005947:Glucose