Chemically synthesized peptides have a free amino group at the N-terminal and a free carboxyl group at the C-terminal end. The acetylation of the N-terminal end and amidation of the C-terminal end does not add a charge to the peptide, this could reduce the solubility of the peptide soemwhat.
However, these modifications are desirable since it imitates the natural structure of a peptide. It increases the metabolic stability of the peptides and their ability to resist enzymatic degradation by aminopeptidases, exopeptidases, and synthetase. These modifications enhance the ability of a peptide to enter cells, and may increase the biological activity. The modifications are recommended if the peptides are used for intracellular, in-vivo assays, or in-vitro studies. These modified peptides can be used as substrates in enzyme assays. Amidation not only enhances the activity of peptide hormones, it also prolongs their shelf life. The modifications can reduce the influence of charged C- or N-terminal during ELISA binding assays.