Submitted to: Journal of Pediatric Gastroenterology and Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 7/1/2207
Publication URL: http://www.jpgn.org
Citation: Quezada-Calvillo, R., Robayo-Torres, C.C., Ao, Z., Hamaker, B.R., Quaroni, A., Brayer, G.D., Sterchi, E.E., Baker, S.S., Nichols, B.L. 2007. Luminal substrate "brake" on mucosal maltase-glucoamylase activity regulates total rate of starch digestion to glucose. Journal of Pediatric Gastroenterology and Nutrition. 45:32-43. Interpretive Summary: This research studied the roles and interactions of two enzymes that are important in the digestion of starch. We conclude that one enzyme (sucrase-isomaltase) constrains glucose production in the presence of a large starch meal. We showed that the human capacity for digestion to glucose is sensitive to the botanical origin of food starches. This principal may be of value in dietary treatment of type 2 diabetes.
Technical Abstract: Starches are the major source of dietary glucose in weaned children and adults. However, small intestine alpha-glucogenesis by starch digestion is poorly understood due to substrate structural and chemical complexity, as well as the multiplicity of participating enzymes. Our objective was dissection of luminal and mucosal alpha-glucosidase activities participating in digestion of the soluble starch product maltodextrin (MDx). Immunoprecipitated assays were performed on biopsy specimens and isolated enterocytes with MDx substrate. Mucosal sucrase-isomaltase (SI) and maltase-glucoamylase (MGAM) contributed 85% of total in vitro alpha-glucogenesis. Recombinant human pancreatic alpha-amylase alone contributed <15% of in vitro alpha-glucogenesis; however, alpha-amylase strongly amplified the mucosal alpha-glucogenic activities by preprocessing of starch to short glucose oligomer substrates. At low glucose oligomer concentrations, MGAM was 10 times more active than SI, but at higher concentrations it experienced substrate inhibition whereas SI was not affected. The in vitro results indicated that MGAM activity is inhibited by alpha-amylase digested starch product "brake" and contributes only 20% of mucosal alpha-glucogenic activity. SI contributes most of the alpha-glucogenic activity at higher oligomer substrate concentrations. MGAM primes and SI activity sustains and constrains prandial alpha-glucogenesis from starch oligomers at approximately 5% of the uninhibited rate. This coupled mucosal mechanism may contribute to highly efficient glucogenesis from low-starch diets and play a role in meeting the high requirement for glucose during children's brain maturation. The brake could play a constraining role on rates of glucose production from higher-starch diets consumed by an older population at risk for degenerative metabolic disorders.