Glc Transporter Assay and the New Intestinal Glycobiology

Abstract

Human and porcine pancreatic α-amylases were found to bind to N-linked glycans of glycoproteins and the component sugar residues of N-glycans including α-mannose, α-N-acetylneuraminic acid, and α-N-acetyllactosamine. Immunostaining revealed that pancreatic α-amylase carbohydrate specifically binds to the brush border membrane (BBM) of enterocytes in the duodenum. The ligands for pancreatic α-amylase in BBM were identified as glycoprotein N-glycans that are significantly involved in the assimilation of glucose, including sucrase-isomaltase (SI) and Na+/Glc cotransporter 1 (SGLT1). Using BBM vesicles, interaction between α-amylase and glycoligands in duodenum BBM was shown to activate glucose production on the one hand and to inhibit glucose absorption by enterocytes via SGLT1 at high but physiologically possible α-amylase concentrations on the other to prevent a rapid increase in blood sugar. A new concept of the modulatory roles of BBM glycoprotein N-glycans and carbohydrate recognition of pancreatic α-amylase, which contribute to blood glucose homeostasis, is presented. The protocol for the Glc transporter assay that gave conclusive evidence for this study is described. Pancreatic α-amylase.