--- title: "Why are so many research peptides acetylated or amidated? | Sable Peptides" description: "N-terminal acetylation and C-terminal amidation across the Sable catalogue: which peptides carry them, what each modification removes, the mass change, and how it relates to the native hormone." canonical: https://www.sablepeptides.co.uk/guides/n-terminal-acetylation-and-c-terminal-amidation-across-the-catalogue dateModified: 2026-10-16 publisher: Sable Peptides Limited (UK company 17488610) note: Research use only. Not for human or veterinary use. --- # 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)](https://pubmed.ncbi.nlm.nih.gov/35124797/); [PAM: diverse roles in neuroendocrine cells, cardiomyocytes, and green algae, FEBS J 2022 (PubMed 34089560)](https://pubmed.ncbi.nlm.nih.gov/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)](https://pubmed.ncbi.nlm.nih.gov/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)](https://pubmed.ncbi.nlm.nih.gov/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 - [Cyclic peptides](/guides/cyclic-peptides-in-the-catalogue-disulfide-and-lactam-rings) - [N-acetyl Epitalon](/guides/epitalon-vs-n-acetyl-epitalon-vs-epitalon-sodium) - [Thymosins](/guides/thymosin-alpha-1-vs-thymosin-beta-4-and-tb-500) - [D-amino acids](/guides/d-amino-acids-in-catalogue-peptides) 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