ARS | Publication request: Sucrase-isomaltase damps rate of mealtime small intestinal mucosal starch oligomer digestion to glucose while maltase-glucoamylase amplifies during snacking

Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2006
Publication Date: May 1, 2006
Citation: Nichols, B.L., Quezada-Calvillo, R., Robayo, C.C., Sterchi, E.E., Baker, S.S. 2006. Sucrase-isomaltase damps rate of mealtime small intestinal mucosal starch oligomer digestion to glucose while maltase-glucoamylase amplifies during snacking [abstract]. Journal of Federation of American Societies for Experimental Biology. 20(4):A575.

Technical Abstract: Food starches contribute about half of the energy content of the human diet. Starches are first hydrolyzed by amylases to soluble glucose oligomers which are hydrolyzed to free glucose by small intestinal sucrase-isomaltase (SI) and maltose-glucoamylase (MGAM). Pooled human duodenal biopsies were assayed for starch digestion activity by partially hydrolyzed starch oligomer substrates. Activities were immunoprecipitated (IPed) with monoclonal antibodies (mAbs) against human SI and MGAM. Kinetics of whole homogenate and IPed activities were assayed with 1 to 16 mM substrate. Enzyme concentrations were measured by scanning blots of the IPs. Mathematical models were built using Michaelis-Menten equation. 80% of starch digesting activity of mucosal homogenates was IPed by SI mAbs. The remainder was IPed by MGAM mAbs. The homogenate SI concentration was 15 ±10 X MGAM. The Km of SI (40 mM) was 10 X higher than MGAM (3.7 mM). MGAM activity was inhibited by 5 mM maltotriose but SI was not. Conclusions: MGAM provides rapid glucose production when snacking and at the beginning and end, but during mid-meal becomes competitively inhibited by lumenal maltotriose. SI has low activity but high capacity for glucose production. The net effect is a "square wave" production of glucose from food starch during meals.