Modifications: N-Terminal Acetylation and C-Terminal Amidation

Free Modifications: N-Terminal Acetylation and C-Terminal Amidation

Chemically synthesized peptides have free N- and C-termini. Please state any need for N-terminal acetylation or C-terminal amidation during the ordering process, because these modifications are introduced during synthesis (amidation requires an amide resin, and acetylation is performed on the resin before cleavage).

N-terminal acetylation and C-terminal amidation reduce the overall charge of a peptide; therefore, its overall solubility might decrease. However, blocking the termini makes a peptide derived from inside a protein sequence a closer mimic of the native protein, which often improves its stability and can increase its biological activity.

Advantages:

• The altered peptide ends are uncharged, so the modified peptides more closely mimic the corresponding region of the native protein. We recommend these modifications for in vitro functional studies, enzyme assays, and in vivo experiments.
• The modifications increase the metabolic stability of peptides as well as their resistance to exopeptidases: N-terminal acetylation slows digestion by aminopeptidases, and C-terminal amidation slows digestion by carboxypeptidases. The modified peptides can then be used as substrates in enzyme assays.
• Amidation not only enhances the activity of peptide hormones, but also prolongs their shelf life.
• The changes reduce the effect of charged C- or N-termini during ELISA binding.

Reference: One published example is a study of channel-blocking peptides (Biophysical Journal Volume 95 November 2008 4879–4889, Figure 2), in which acetylating the N-terminus and amidating the C-terminus improved the channel-blocking efficiency of the peptides (Figure 2).