Many natural and synthetic peptides end in an amide rather than a free acid. The amide removes the C-terminal negative charge and can make the peptide more resistant to carboxypeptidases in in vitro systems.
Amidation lowers the mass by 0.98 Da compared with the free acid, a difference that mass spectrometry can resolve, so the C-terminal form is part of a peptide's identity. Amidated peptides are made on resins (such as Rink amide) that release the amide on cleavage.
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.