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Oxytocin is an endogenous cyclic nonapeptide and principal agonist of the oxytocin receptor (OXTR). Its sequence, CYIQNCPLG-NH₂, contains an intramolecular Cys1-Cys6 disulfide bridge that forms a six-residue cyclic core followed by a short Pro-Leu-Gly-NH₂ tail.
The compact molecular architecture makes oxytocin a useful model for studying neurohypophysial peptide recognition, GPCR signaling, receptor internalization and the pharmacological overlap between oxytocin and vasopressin receptor systems.
Product Information
| Property | Specification |
|---|---|
| Product Name | Oxytocin |
| CAS No. | 50-56-6 |
| Sequence | Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH₂ |
| One-Letter Sequence | CYIQNCPLG-NH₂ |
| Peptide Length | 9 amino-acid residues |
| Molecular Formula | C43H66N12O12S2 |
| Molecular Weight | Approximately 1007.2 Da |
| Disulfide Bond | Cys1-Cys6 |
| C-Terminus | Gly-NH₂ |
| Primary Receptor | Oxytocin receptor / OXTR |
| Receptor Family | Oxytocin / vasopressin GPCR family |
Cyclic Architecture of the Native Peptide
Oxytocin contains four residues outside the immediate disulfide linkage context but only two cysteines, positioned at residues 1 and 6. Oxidation of these thiols creates the characteristic ring of the mature hormone.
The Pro7-Leu8-Gly9-NH₂ tail extends beyond the cyclic region and also contributes to receptor recognition. C-terminal amidation should therefore be regarded as part of the native chemical identity rather than an optional synthetic modification.
Oxytocin Receptor Signaling
OXTR is a rhodopsin-family GPCR most commonly associated with Gq/11-dependent signaling. Receptor activation can stimulate phospholipase C, generate inositol phosphates and mobilize intracellular Ca2+.
The receptor can also engage additional G-protein and β-arrestin-dependent pathways depending on cellular context. This makes oxytocin useful for experiments extending beyond a single calcium endpoint.
Receptor Desensitization and Internalization
After agonist stimulation, OXTR can undergo phosphorylation, recruit β-arrestins and internalize from the plasma membrane. Receptor trafficking can subsequently lead to recycling or degradation depending on the cellular system and duration of stimulation.
For experiments comparing acute and prolonged exposure, we recommend recording ligand concentration and stimulation time because receptor availability and signaling state can change substantially after sustained agonist treatment.
Oxytocin Is Not Absolutely OXTR-Specific
Oxytocin and arginine vasopressin differ by only two amino-acid residues and act through closely related receptor families. Pharmacological overlap is therefore biologically relevant.
Oxytocin has measurable agonist activity at vasopressin receptors, particularly V1a, although its affinity is generally lower than that of AVP at those receptors.
High peptide concentrations can consequently produce responses outside the intended OXTR pathway. We recommend receptor-selective controls when experiments are intended to assign a biological response specifically to OXTR.
Oxytocin and Argipressin
| Feature | Oxytocin | Argipressin |
|---|---|---|
| Length | 9 residues | 9 residues |
| Position 3 | Ile | Phe |
| Position 8 | Leu | Arg |
| Disulfide Bond | Cys1-Cys6 | Cys1-Cys6 |
| Primary Receptor Preference | OXTR | Vasopressin receptors |
The close sequence relationship provides a natural structure–activity system for studying receptor discrimination within the oxytocin–vasopressin family.
Experimental and Quality Considerations
Correct disulfide formation and C-terminal amidation should be confirmed when oxytocin is used for quantitative receptor studies. Reduced or incorrectly oxidized material should not be treated as equivalent to the native cyclic form.
Our Peptide Quality Control capabilities support analytical HPLC and mass spectrometry according to the selected specification.
Research Applications
Oxytocin can support OXTR pharmacology, intracellular calcium assays, receptor internalization and trafficking studies, neuroendocrine research, peptide structure–activity analysis and comparison with vasopressin-family ligands.
A defined acetate form is available as Oxytocin Acetate.
Modified cyclic peptides, receptor-selective analogs and labeled oxytocin derivatives can be evaluated through Chemical Peptide Synthesis.
Frequently Asked Questions
What is the sequence of Oxytocin?
The sequence is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH₂, abbreviated CYIQNCPLG-NH₂.
Which cysteines form the Oxytocin disulfide bond?
Cys1 and Cys6 form the intramolecular disulfide bridge.
Does Oxytocin activate only OXTR?
No. OXTR is its principal receptor, but measurable agonist activity can also occur at vasopressin-family receptors depending on concentration, species and receptor expression.
Is Oxytocin the same chemical entity as Oxytocin Acetate?
The active peptide sequence is the same, but Oxytocin Acetate includes an associated acetate counterion and therefore has a different defined salt composition and molecular weight.