Figure 1: Locations of the epsilon Nitrogen, isopeptide bond, and peptide bond.

An Isopeptide bond usually occurs with the amino group of lysine or the carboxyl group of glutamate. In a peptide bond, which joins amino acids in a polypeptide, bonds form with the carboxyl and amino groups attached to a common alpha-carbon. With amino acids which happen to contain a carboxyl or amino group in their side chain, it is possible for an isopeptide bond to form.

An example of a small peptide containing an isopeptide bond is glutathione, which has a bond between the side chain of a glutamate residue and the amino group of a cysteine residue. An example of a protein involved in isopeptide bonding is ubiquitin, which gets attached to other proteins with a bond between the C-terminal glycine residue of ubiquitin and a lysine side chain of the substrate protein.

See also

• Organic Chemistry
• Biochemistry