title: Contribution of mucosal maltase-glucoamylase activities to mouse small intestinal starch alpha-glucogenesis.
abstract: Digestion of starch requires activities provided by 6 interactive small intestinal enzymes. Two of these are luminal endo-glucosidases named alpha-amylases. Four are exo-glucosidases bound to the luminal surface of enterocytes. These mucosal activities were identified as 4 different maltases. Two maltase activities were associated with sucrase-isomaltase. Two remaining maltases, lacking other identifying activities, were named maltase-glucoamylase. These 4 activities are better described as alpha-glucosidases because they digest all linear starch oligosaccharides to glucose. Because confusion persists about the relative roles of these 6 enzymes, we ablated maltase-glucoamylase gene expression by homologous recombination in Sv/129 mice. We assayed the alpha-glucogenic activities of the jejunal mucosa with and without added recombinant pancreatic alpha-amylase, using a range of food starch substrates. Compared with wild-type mucosa, null mucosa or alpha-amylase alone had little alpha-glucogenic activity. alpha-Amylase amplified wild-type and null mucosal alpha-glucogenesis. alpha-Amylase amplification was most potent against amylose and model resistant starches but was inactive against its final product limit-dextrin and its constituent glucosides. Both sucrase-isomaltase and maltase-glucoamylase were active with limit-dextrin substrate. These mucosal assays were corroborated by a 13C-limit-dextrin breath test. In conclusion, the global effect of maltase-glucoamylase ablation was a slowing of rates of mucosal alpha-glucogenesis. Maltase-glucoamylase determined rates of digestion of starch in normal mice and alpha-amylase served as an amplifier for mucosal starch digestion. Acarbose inhibition was most potent against maltase-glucoamylase activities of the wild-type mouse. The consortium of 6 interactive enzymes appears to be a mechanism for adaptation of alpha-glucogenesis to a wide range of food starches.
authors.affiliation: CIEP-Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosi, Zona Universitaria, San Luis Potosí, S.L.P., Mexico 78360.
authors.forename: Roberto
authors.initials: R
authors.lastname: Quezada-Calvillo
authors.forename: Claudia C
authors.initials: CC
authors.lastname: Robayo-Torres
authors.forename: Antone R
authors.initials: AR
authors.lastname: Opekun
authors.forename: Partha
authors.initials: P
authors.lastname: Sen
authors.forename: Zihua
authors.initials: Z
authors.lastname: Ao
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Hamaker
authors.forename: Andrea
authors.initials: A
authors.lastname: Quaroni
authors.forename: Gary D
authors.initials: GD
authors.lastname: Brayer
authors.forename: Sigrid
authors.initials: S
authors.lastname: Wattler
authors.forename: Michael C
authors.initials: MC
authors.lastname: Nehls
authors.forename: Erwin E
authors.initials: EE
authors.lastname: Sterchi
authors.forename: Buford L
authors.initials: BL
authors.lastname: Nichols
mesh_terms: D020909:Acarbose / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000096:biosynthesis*; D007413:Intestinal Mucosa / Q000201:enzymology*; D007534:Isomaltose / Q000378:metabolism; D007583:Jejunum / Q000201:enzymology*; D008320:Maltose / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D013213:Starch / Q000378:metabolism*; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D007534:Isomaltose; D008320:Maltose; D013213:Starch; D000520:alpha-Glucosidases; D005947:Glucose; D020909:Acarbose