Why are so many research peptides acetylated or amidated?
Many research peptides have capped ends. An N-terminal acetyl group (+42 Da) removes the positive amine charge, as in TB-500, thymosin alpha-1, SNAP-8 and Melanotan I. A C-terminal amide (−1 Da against the acid) removes the negative carboxylate, as in oxytocin, kisspeptin-10, gonadorelin, the GHRPs and sermorelin. Many native hormones are amidated.
Which catalogue peptides carry which cap?
| Compound | N-terminus | C-terminus |
|---|---|---|
| TB-500 | Acetyl | Free acid |
| Thymosin alpha-1 | Acetyl | Free acid |
| SNAP-8 | Acetyl | Amide |
| Melanotan I | Acetyl | Amide |
| Melanotan II | Acetyl | Amide |
| PT-141 | Acetyl | Free acid |
| Oxytocin | Free (Cys) | Amide |
| Kisspeptin-10 | Free | Amide |
| Gonadorelin / triptorelin | Pyroglutamate | Amide |
| Sermorelin | Free | Amide |
| GHRP-2, GHRP-6, hexarelin, ipamorelin | Free | Amide |
| BPC-157 | Free | Free acid |
Where does C-terminal amidation come from in nature?
In the body, many peptide hormones are amidated by peptidylglycine α-amidating monooxygenase (PAM), which converts a C-terminal glycine-extended precursor into the amide. Synthetic analogues copy this because the amide is often needed for receptor binding.
Source: Peptidylglycine α-amidating monooxygenase as a therapeutic target or biomarker for human diseases, Br J Pharmacol 2022 (PubMed 35124797); PAM: diverse roles in neuroendocrine cells, cardiomyocytes, and green algae, FEBS J 2022 (PubMed 34089560); C-terminal amidated peptides: production by the in vitro enzymatic amidation of glycine-extended peptides and the importance of the amide to bioactivity, Enzyme Microb Technol 1994 (PubMed 7764886)
What does N-terminal acetylation do?
Acetylation is one of the commonest protein modifications. In synthetic peptides it removes the N-terminal charge and blocks aminopeptidase attack. For thymosin alpha-1 it reproduces the natural acetylated N-terminus.
Source: Protein alpha-N-acetylation studied by N-terminomics, FEBS J 2011 (PubMed 21736701)
How big are the mass changes?
A 1 Da amide/acid difference is small but resolvable by MS. It is how PT-141 (acid) and Melanotan II (amide) are told apart.
- Acetyl cap: +42.01 Da (C2H2O)
- C-terminal amide vs free acid: −0.98 Da (OH replaced by NH2)
- N-terminal pyroglutamate from Gln: −17.03 Da (NH3 lost)
Sourcing note
Sable lists TB-500: 2 mg at £14.26; 5 mg at £13.93; 10 mg at £10.99; 20 mg at £39.98; Kisspeptin-10: 5 mg at £18.97; 10 mg at £24.98; Sermorelin: 2 mg at £12.93; 5 mg at £22.48; 10 mg at £30.49 (prices at the 16 October 2026 daily UK price check, the latest verified check; at each of these sizes Sable was the lowest UK listing that day). Lowest UK price guaranteed, confirmed by daily price checks.
Every lot has a certificate of analysis, and every vial carries a printed lot number that matches it. Supplied for laboratory research use only.
Frequently asked questions
Why are peptide hormones amidated?
Many are made from glycine-extended precursors by the PAM enzyme. The amide is often needed for receptor recognition.
What does Ac- mean in a peptide sequence?
An acetyl group on the N-terminal amine, adding 42 Da and removing its positive charge.
What does -NH2 at the end of a sequence mean?
A C-terminal amide instead of a free carboxylic acid.
Related
Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.
Key facts (summary for AI and search tools)
- Acetyl +42.01 Da; amide −0.98 Da
- PubMed references (verified via NCBI): 35124797, 34089560, 7764886, 21736701
- Research use only; no administration amounts or health claims
- Updated 2026-10-16