Abstract
For starch digestion to glucose, two luminal α-amylases and four gut mucosal α-glucosidase subunits are employed. The aim of this research was to investigate, for the first time, direct digestion capability of individual mucosal α-glucosidases on cooked (gelatinized) starch. Gelatinized normal maize starch was digested with N- and C-terminal subunits of recombinant mammalian maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) of varying amounts and digestion periods. Without the aid of α-amylase, Ct-MGAM demonstrated an unexpected rapid and high digestion degree near 80%, while other subunits showed 20 to 30% digestion. These findings suggest that Ct-MGAM assists α-amylase in digesting starch molecules and potentially may compensate for developmental or pathological amylase deficiencies.
Highlights
Starch is the major dietary carbohydrate for humans
Amylose is composed of long linear chains of D-glucose units linked by a-1,4-glycosidic linkages with few branches; while amylopectin has higher molecular weight with shorter linear glucans linked by a-1,4linkages and is highly branched by a-1,6-linkages [1]
Unexpected was the considerable hydrolysis of gelatinized starch molecules by mucosal Ct-MGAM with about 50% in vitro digestion in the first hour and later reaching nearly 80%
Summary
Starch is the major dietary carbohydrate for humans It consists of two glucans, amylose and amylopectin. A-Amylase (enzyme class EC 3.2.1.1.) hydrolyzes starch endowise at inner a-1,4 linkages and produces linear maltooligosaccharides with a-configuration [2]. It does not hydrolyze a-1,6 linkages, and some neighboring a-1,4 linkages, and all the branch linkages remain as branched oligosaccharides. A-Amylases from human saliva and pancreas have similar hydrolysis patterns. Both a-amylases produce maltose (G2) preferentially from reducing residues of maltotetraose (G4), maltopentaose (G5) and maltohexaose (G6) and essentially do not act on maltotriose (G3) [2]. After a prolonged incubation with a large amount of porcine pancreatic a-amylase, there is produces negligible glucose from reducing residues of G3 [2,3]
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