---
title: "Oxytocin: structure, disulfide ring and research background | Sable Peptides"
description: "Oxytocin is a cyclic nonapeptide with a Cys1–Cys6 disulfide and an amidated C-terminus. Its structure compared with vasopressin, PubChem data, the 2020 receptor crystal structure, and what this means for lab handling."
canonical: https://www.sablepeptides.co.uk/guides/oxytocin-structure-disulfide-ring-and-research-background
dateModified: 2026-10-16
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# 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](https://pubchem.ncbi.nlm.nih.gov/compound/439302)

## 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 |

Source: [The oxytocin receptor system: structure, function, and regulation, Physiol Rev 2001 (PubMed 11274341)](https://pubmed.ncbi.nlm.nih.gov/11274341/)

## 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.

Source: [The Nobel Prize in Chemistry 1955 (nobelprize.org)](https://www.nobelprize.org/prizes/chemistry/1955/summary/)

## 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)](https://pubmed.ncbi.nlm.nih.gov/32832646/); [Vasopressin and oxytocin release within the brain: a dynamic concept of multiple and variable modes of neuropeptide communication, Front Neuroendocrinol 2004 (PubMed 15589267)](https://pubmed.ncbi.nlm.nih.gov/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](/guides/cyclic-peptides-in-the-catalogue-disulfide-and-lactam-rings)
-   [Oxytocin research vials](/products/oxytocin)
-   [Kisspeptin-10, gonadorelin and triptorelin](/guides/kisspeptin-10-gonadorelin-and-triptorelin-compared)
-   [LL-37 structure](/guides/ll-37-human-cathelicidin-structure-and-research)

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