Dipeptides

Dipeptides are peptides composed of two amino-acid residues. In a typical linear dipeptide, the carboxyl group of one amino acid is joined to the amino group of another by a peptide bond. This leaves one amino end, called the N-terminus, and one carboxyl end, called the C-terminus. The order of the two amino acids matters, so glycylalanine and alanylglycine are chemically distinct dipeptides .¹

Dipeptides can form when proteins and larger peptides are broken down by proteolytic enzymes. During digestion, gastric, pancreatic, and intestinal enzymes progressively hydrolyze dietary proteins into smaller peptides and free amino acids. Dipeptides, together with tripeptides and amino acids, are therefore important products of intestinal protein digestion .^2,3

In the small intestine, many dipeptides are taken into enterocytes through peptide transporter 1 (PEPT1). PEPT1 is located in the brush-border membrane and uses a proton electrochemical gradient to transport dipeptides and tripeptides into the cell. Free amino acids use different transport systems. Once inside enterocytes, most absorbed dipeptides and tripeptides are further hydrolyzed by intracellular peptidases into their component amino acids .^2,3

A dipeptide is therefore distinct from two separate free amino acids. Its two amino-acid residues are chemically joined as a single molecule by a peptide bond. It is also distinct from a tripeptide, which contains three amino-acid residues .^1,2