title: Maltase-glucoamylase modulates gluconeogenesis and sucrase-isomaltase dominates starch digestion glucogenesis.
abstract: OBJECTIVE
  Six enzyme activities are needed to digest starch to absorbable free glucose; 2 luminal α-amylases (AMY) and 4 mucosal maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) subunit activities are involved in the digestion. The AMY activities break down starch to soluble oligomeric dextrins; mucosal MGAM and SI can either directly digest starch to glucose or convert the post-α-amylolytic dextrins to glucose. We hypothesized that MGAM, with higher maltase than SI, drives digestion on ad limitum intakes and SI, with lower activity but more abundant amount, constrains ad libitum starch digestion.
  
  
  METHODS
  Mgam null and wild-type (WT) mice were fed with starch diets ad libitum and ad limitum. Fractional glucogenesis (fGG) derived from starch was measured and fractional gluconeogenesis and glycogenolysis were calculated. Carbohydrates in small intestine were determined.
  
  
  RESULTS
  After ad libitum meals, null and WT had similar increases of blood glucose concentration. At low intakes, null mice had less (f)GG (P = 0.02) than WT mice, demonstrating the role of Mgam activity in ad limitum feeding; null mice did not reduce fGG responses to ad libitum intakes demonstrating the dominant role of SI activity during full feeding. Although fGG was rising after feeding, fractional gluconeogenesis fell, especially for null mice.
  
  
  CONCLUSIONS
  The fGNG (endogenous glucogenesis) in null mice complemented the fGG (exogenous glucogenesis) to conserve prandial blood glucose concentrations. The hypotheses that Mgam contributes a high-efficiency activity on ad limitum intakes and SI dominates on ad libitum starch digestion were confirmed.
authors.affiliation: *USDA/ARS Children's Nutrition Research Center and the Department of Pediatrics, Baylor College of Medicine, Houston, TX †Whistler Center for Carbohydrate Research, Department of Food Sciences, Purdue University, West Lafayette, IN.
authors.forename: Maricela
authors.initials: M
authors.lastname: Diaz-Sotomayor
authors.forename: Roberto
authors.initials: R
authors.lastname: Quezada-Calvillo
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Avery
authors.forename: Shaji K
authors.initials: SK
authors.lastname: Chacko
authors.forename: Li-Ke
authors.initials: LK
authors.lastname: Yan
authors.forename: Amy Hui-Mei
authors.initials: AH
authors.lastname: Lin
authors.forename: Zi-hua
authors.initials: ZH
authors.lastname: Ao
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Hamaker
authors.forename: Buford L
authors.initials: BL
authors.lastname: Nichols
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004063:Digestion / Q000235:genetics; D005943:Gluconeogenesis; D005947:Glucose / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000201:enzymology / Q000378:metabolism; D007421:Intestine, Small / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D019518:Postprandial Period; D013213:Starch / Q000378:metabolism*; D013394:Sucrase-Isomaltase Complex / Q000378:metabolism*; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D013213:Starch; D013394:Sucrase-Isomaltase Complex; D000520:alpha-Glucosidases; D005947:Glucose