Proton-coupled peptide transport in the small intestine and kidney

Abstract

Carrier-mediated transport of small peptides is a well established phenomenon in the small intestine and kidney (Ganapathy & Leibach, 1986, 1991; Ganapathy et al., 1991; Matthews, 1991; Silbernagl, 1988). In the small intestine, absorption of intact peptides into the enterocytes across the brush border membrane via the peptide transport system plays an important role in the assimilation of dietary proteins. The substrates for the peptide transport system are generated by concerted actions of gastric and pancreatic proteases and brush border peptidases. Of these enzymes, dipeptidylpeptidase IV (DPP IV) and angiotensin converting enzyme (ACE), both of which are associated with the brush border membrane, are of significant importance because they directly generate dipeptides from the amino terminus and the carboxy terminus respectively, of large polypeptides and proteins by sequential action. The enterocytes, in addition, possess highly active cytosolic peptidases which hydrolyze the peptides entering the cell via the brush border membrane peptide transport system. Thus, even though protein digestion products are absorbed into the enterocytes to an appreciable extent in the form of intact peptides, what enters the circulation is predominantly in the form of free amino acids.