Oxytocin: structure, disulfide ring and research background
Oxytocin is a nine-residue peptide, Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2. A disulfide bond between Cys1 and Cys6 closes a six-residue ring, and a three-residue tail ends in a C-terminal amide. Its molecular weight is about 1007 g/mol. It was the first peptide hormone to be chemically synthesised, in 1953.
What is the structure of oxytocin?
- Class: cyclic nonapeptide
- Sequence: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (Cys1-Cys6 disulfide)
- Molecular formula (PubChem): C43H66N12O12S2
- Molecular weight (PubChem): 1007.20 g/mol
- CAS: 50-56-6
- Ring: residues 1–6 closed by the Cys1–Cys6 disulfide
- Tail: Pro7-Leu8-Gly9-NH2
Source: PubChem CID 439302: Oxytocin
How does oxytocin differ from vasopressin?
The two hormones differ at two positions only, which is why receptor cross-reactivity is a recurring theme in the literature.
| Position | Oxytocin | Arginine vasopressin |
|---|---|---|
| 3 | Ile | Phe |
| 8 | Leu | Arg |
| Other positions | Identical framework: Cys1–Cys6 ring, Pro7, Gly9-NH2 | Same |
Why was oxytocin historically important?
Vincent du Vigneaud's synthesis of oxytocin was cited in his 1955 Nobel Prize in Chemistry, awarded for the first synthesis of a polypeptide hormone.
What is known about the oxytocin receptor's structure?
A crystal structure of the human oxytocin receptor, a class A GPCR, was published in 2020. Earlier work described how oxytocin is released within the brain, not only into the circulation.
Source: Crystal structure of the human oxytocin receptor, Sci Adv 2020 (PubMed 32832646); Vasopressin and oxytocin release within the brain: a dynamic concept of multiple and variable modes of neuropeptide communication, Front Neuroendocrinol 2004 (PubMed 15589267)
What does the disulfide mean for a laboratory sample?
The intact disulfide is part of identity. A reduced (open-chain) form is 2 Da heavier and is a recognisable impurity by mass spectrometry. Oxytocin contains no Met or Trp, but the disulfide can scramble or reduce under harsh conditions.
Sourcing note
Sable lists Oxytocin: 5 mg at £23.98 (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
How many amino acids are in oxytocin?
Nine: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with a Cys1–Cys6 disulfide.
What is the difference between oxytocin and vasopressin?
They differ at positions 3 (Ile vs Phe) and 8 (Leu vs Arg). The rest of the structure is the same.
What is the molecular weight of oxytocin?
About 1007.2 g/mol (PubChem CID 439302), formula C43H66N12O12S2.
Related
- Which catalogue peptides are cyclic, and how are their rings formed
- Oxytocin research vials
- Kisspeptin-10, gonadorelin and triptorelin
- LL-37 structure
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)
- Oxytocin PubChem CID 439302
- Cys1–Cys6 disulfide; C-terminal amide
- PubMed references (verified via NCBI): 11274341, 32832646, 15589267
- PubChem CIDs: 439302
- Research use only; no administration amounts or health claims
- Updated 2026-10-16