Alpha‐glucogenic activity of mammalian mucosal enzymes on different disaccharides

Small intestine mucosal maltase‐glucoamylase (MGAM) and sucrase‐isomaltase (SI) have two subunits each (N‐ and C‐ terminal) that are involved in the digestion of glycemic carbohydrates to glucose and fructose from diets. In this study, recombinant MGAM and SI enzymes were reacted with disaccharides, namely kojibiose, nigerose, maltose, and isomaltose each containing two glucose molecules as well as sucrose, but with different á‐linkages, to elucidate their digestion abilities. Reactions were carried at 37°C in 10 mM PBS and one unit (U) enzyme activity was defined as 1 μg of glucose released from maltose per 10 min. After enzyme reactions, released glucose was measured by the GOPOD method. Notably, each of the four subunits had á‐(1, 2), (1, 3) and (1, 4) hydrolysis activities, but N‐SI at 100 U was the only one to have á‐(1, 6) hydrolysis activity. Moreover, every subunit had á‐(1, 6) hydrolysis activity at higher enzyme concentration (above 2500 U of subunits except N‐SI). Each subunit had á‐glucosidase activity on different glycosidic linkages though maltase activity was at least 25 times greater than isomaltase activity. Also, only C‐SI and C‐MGAM showed sucrase activity with relatively lower than maltase activity. This is the first report of á‐glucogenic activity of disaccharides for each mucosal enzyme subunit and provides a new view of carbohydrate digestion model in the small intestine. Grant Funding Source : CNRC/ARS/USDA