Luminal substrate "brake" on mucosal maltase-glucoamylase activity regulates total rate of starch digestion to glucose

Quezada-Calvillo, Roberto; Robayo-Torres, Claudia C; Ao, Zihua; Hamaker, Bruce R; Quaroni, Andrea; Brayer, Gary D; Sterchi, Erwin E; Baker, Susan S; Nichols, Buford 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(1), pp. 32-43. Hagerstown, Md.: Lippincott Williams & Wilkins 10.1097/MPG.0b013e31804216fc

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BACKGROUND: 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). PATIENTS AND METHODS: Immunoprecipitated assays were performed on biopsy specimens and isolated enterocytes with MDx substrate. RESULTS: 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. CONCLUSIONS: 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.

Item Type:

Journal Article (Original Article)

Division/Institute:

04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Biochemistry and Molecular Medicine

UniBE Contributor:

Sterchi, Erwin-Ernst

ISSN:

0277-2116

ISBN:

17592362

Publisher:

Lippincott Williams & Wilkins

Language:

English

Submitter:

Factscience Import

Date Deposited:

04 Oct 2013 14:53

Last Modified:

17 Mar 2015 21:59

Publisher DOI:

10.1097/MPG.0b013e31804216fc

PubMed ID:

17592362

Web of Science ID:

000247551100006

URI:

https://boris.unibe.ch/id/eprint/22698 (FactScience: 36071)

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