Submitted to: Federation of European Biochemical Societies Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 7/1/2007
Citation: Ao, Z., Quezada-Calvillo, R., Sim, L., Nichols, B.L., Rose, D.R., Sterchi, E.E., Hamaker, B.R. 2007. Evidence of native starch degradation with human small intestinal maltase-glucoamylase (recombinant). FEBS Letters. 581:2381-2388. Interpretive Summary: Contemporary theory states that amylase digestion is required before starch can be converted to absorbable glucose. In this study recombinant N-terminal human recombinant maltase-glucoamylase was used to digest genetically engineered starch granules. The experiments were done with and without added human pancreatic amylase. We found that maltase-glucoamylase can digest starch granules without amylase but that addition of amylase amplifies the rate of maltase-glucoamylase glucose production from starch. These findings suggest that the recombinant enzyme can be used to redefine the resistance of native starches to glucose digestion. We showed that the botanical source of the starch plays a major role in starch digestion by maltase-glucoamylase and may be of value in dietary treatment of type 2 diabetes.
Technical Abstract: Action of human small intestinal brush border carbohydrate digesting enzymes is thought to involve only final hydrolysis reactions of oligosaccharides to monosaccharides. In vitro starch digestibility assays use fungal amyloglucosidase to provide this function. In this study, recombinant N-terminal subunit enzyme of human small intestinal maltase-glucoamylase (rhMGAM-N) was used to explore digestion of native starches from different botanical sources. The susceptibilities to enzyme hydrolysis varied among the starches. The rate and extent of hydrolysis of amylomaize-5 and amylomaize-7 into glucose were greater than for other starches. Such was not observed with fungal amyloglucosidase or pancreatic alpha-amylase. The degradation of native starch granules showed a surface furrowed pattern in random, radial, or tree-like arrangements that differed substantially from the erosion patterns of amyloglucosidase or alpha-amylase. The evidence of raw starch granule degradation with rhMGAM-N indicates that pancreatic alpha-amylase hydrolysis is not a requirement for native starch digestion in the human small intestine.