Regulatory Functions of α-Amylase in the Small Intestine Other than Starch Digestion: α-Glucosidase Activity, Glucose Absorption, Cell Proliferation, and Differentiation

Abstract

Pancreatic α-amylase binds to the N-glycan of glycoproteins. Here, I will show that pancreatic α-amylase has regulatory functions in the small intestine other than starch digestion. These new functions were revealed by identification of α-amylase-binding proteins in the intestinal brush border membrane (BBM). This topic will include the following four parts: 1) identification of glycoproteins that bind pancreatic α-amylase in the small intestinal BBM; 2) interactions between pancreatic α-amylase and the binding glycoproteins, sucrose-isomaltase (α-glucosidase), and sodium/glucose co-transporter 1 (SGLT1), in which pancreatic α-amylase enhanced maltose degradation of sucrose-isomaltase under conditions including calcium and sodium, and inhibited glucose uptake of SGLT1; 3) localization of pancreatic α-amylase in the small intestine by binding to the BBM and being internalized into lysosomes through the endocytic pathway; and 4) expression of endogenous α-amylase in the duodenum: AMY2B, a pancreatic type α-amylase, is highly expressed in the human duodenum next to the pancreas. The α-amylase expression in the duodenum is required for proliferation and differentiation of human small intestinal epithelial cells.