Oxytocin is a cyclic nonapeptide — nine amino acids, Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, closed into a six-residue ring by a disulfide bridge between the two cysteines, with a three-residue tail terminating in an amide. Molecular formula C43H66N12O12S2, molecular weight 1007.19 g/mol.
It occupies a particular place in the history of the field: oxytocin was the first polypeptide hormone to be sequenced and then chemically synthesised, work by Vincent du Vigneaud that won the 1955 Nobel Prize in Chemistry and established that biologically active peptides could be built to specification in a laboratory. Essentially every synthetic peptide in this catalogue descends from that demonstration.
Research context
Published research covers signalling through the oxytocin receptor, a G-protein-coupled receptor expressed in uterine and mammary tissue and across several regions of the central nervous system. Peripheral work concerns smooth muscle contraction; central work examines social recognition, pair bonding and anxiety-related endpoints in animal models.
Two structural details matter for handling. The disulfide bridge is essential to activity — reduce it and the molecule loses its conformation. And oxytocin differs from vasopressin at only two of nine positions, so cross-reactivity at vasopressin receptors is a real consideration in experimental design rather than a theoretical one.
For a fuller treatment of the sequence, published models and technical data, see the Oxytocin research guide.
Specification
CAS number 50-56-6. Supplied as a white lyophilized powder, soluble in water. This batch assayed at 99.45% purity, verified by HPLC and LC-MS at ILS Lab.
Handling
Reconstitute with bacteriostatic or sterile water, introducing the diluent against the vial wall and swirling gently rather than shaking. Avoid reducing agents in buffer preparations, which will cleave the disulfide bridge and inactivate the peptide.
Store lyophilized at −20°C protected from light; refrigerate at 2–8°C once reconstituted.
Ships with a batch-specific Certificate of Analysis. Cross-check the batch ID printed on your vial against the CoA before use — see the guide to reading a CoA if you are unfamiliar with the format.
Frequently asked questions about oxytocin
Why must reducing agents be avoided?
Because the disulfide bridge between Cys1 and Cys6 is what holds the molecule in its active conformation. Reducing agents — DTT, TCEP, beta-mercaptoethanol — cleave that bond, and the ring opens into a linear peptide that no longer binds the receptor. The amino acid sequence is unchanged, so the loss is invisible to a simple mass check. Screen buffer components before use.
Does oxytocin cross-react with vasopressin receptors?
Yes, and it is a practical concern rather than a theoretical one. Oxytocin and vasopressin differ at only two of nine positions, and the receptors are correspondingly similar. Cross-reactivity has to be controlled for in experimental design — particularly in central nervous system work where both receptor families are expressed and endpoints can be driven by either.
What makes oxytocin historically significant?
It was the first polypeptide hormone to be sequenced and then chemically synthesised — work by Vincent du Vigneaud that won the 1955 Nobel Prize in Chemistry. That demonstration established that biologically active peptides could be built to specification in a laboratory rather than only extracted from tissue. Every synthetic peptide in this catalogue descends from it.
How stable is oxytocin in solution?
Reasonably stable if the disulfide bridge is protected. The main risks are reducing agents, elevated pH which promotes disulfide scrambling, and repeated freeze-thaw cycles. Reconstitute with bacteriostatic or sterile water, swirl gently rather than shaking, store lyophilized at −20°C protected from light and refrigerate at 2–8°C once reconstituted.
Research use only. Not for human or veterinary use, not for use in diagnostic procedures, and not evaluated by the U.S. Food and Drug Administration.
