Evidence of native starch degradation with human small intestinal maltase‐glucoamylase (recombinant)

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 (rhM-GAM-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 a-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 a-amylase. The evidence of raw starch granule degradation with rhMGAM-N indicates that pancreatic a-amylase hydrolysis is not a requirement for native starch digestion in the human small intestine.

Effect of Novel Maize-based Dietary Fibers on Postprandial Glycemia and Insulinemia

“…AMG primarily hydrolysis smaller molecules and can cleave both ␣-1,4 and 1,6-glycosidic bonds [35,36]. The action of fungal AMG used in vitro has been shown to be significantly different from the action of human brushborder enzymes [35] making a correlation of in vitro to in vivo digestion more difficult for samples that are significantly digested by these enzymes. Pullulan, Soluble Corn Fiber-70 and Soluble Fiber Dextrin are products that are much more affected by the action of amyloglucosidase (in vitro) or brush border enzymes (in vivo).…”

“…AMG is added in vitro assays to mimic the action of brushborder enzymes present in the human body and to prevent ␣-amylase inhibition of small molecular weight digestion products in vitro [34]. AMG primarily hydrolysis smaller molecules and can cleave both ␣-1,4 and 1,6-glycosidic bonds [35,36]. The action of fungal AMG used in vitro has been shown to be significantly different from the action of human brushborder enzymes [35] making a correlation of in vitro to in vivo digestion more difficult for samples that are significantly digested by these enzymes.…”

Unexpected High Digestion Rate of Cooked Starch by the Ct-Maltase-Glucoamylase Small Intestine Mucosal α-Glucosidase Subunit

“…Our research group has investigated gut mucosal α-glucosidase digestion at various starch structural levels. Recombinant human Nt-MGAM was found to be capable, albeit at a very low rate, to digest intact starch granules to glucose [34]. Mucosal α-glucosidase digestion was also examined at the α-limit dextrin (LDx) level.…”

Copy Number Polymorphism of the Salivary Amylase Gene: Implications in Human Nutrition Research

“…MGAM is more active than SIM at low concentrations of oligosaccharides, while MGAM, contrary to SIM, is inhibited by substrate at high oligomer concentration. Interestingly, it has been shown that MGAM is able to hydrolyze not only malto-oligosaccharides of low molecular weight, but also undigested large native starch chains in the intestine [40]. The enormous surface provided by the villi and microvilli of the brush border of the small intestine area ensures complete absorption of glucose [4] that is transported via the hepatic portal vein to the liver.…”