Oxytocin Amino Acid Sequence
Understanding the precise amino acid sequence and structural conformation of oxytocin is critical for designing valid in vitro assays, receptor-binding studies, and preclinical research. This reference guide provides the primary structure, biochemical characteristics, comparison metrics, and analytical standards required for rigorous laboratory experimentation.
Quick answer
Understanding the precise amino acid sequence and structural conformation of oxytocin is critical for designing valid in vitro assays, receptor-binding studies, and preclinical research. This reference guide provides the primary structure, biochemical characteristics, comparison metrics, and analytical standards required for rigorous laboratory experimentation.
Key takeaways
- The [oxytocin](/research-peptides/oxytocin) amino acid sequence is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (CYIQNCPLG-NH2).
- The primary structure of [oxytocin](/research-peptides/oxytocin) consists of nine standard L-amino acid residues arranged in a conserved sequence: L-Cysteinyl-L-Tyrosyl-L-Isoleucyl-L-Glutaminyl-L-Asparaginyl-L-Cysteinyl-L-Prolyl-L-Leucyl-Glycinamide.
- [Oxytocin](/research-peptides/oxytocin) belongs to a highly conserved superfamily of neurohypophyseal peptide hormones that share high sequence homology with arginine vasopressin.
- In vitro models demonstrate that [oxytocin](/research-peptides/oxytocin) acts as a full agonist at the human oxytocin receptor (OXTR), a Class A Rhodopsin-like G-protein coupled receptor (GPCR).
Direct Chemical Overview of the Oxytocin Amino Acid Sequence
The oxytocin amino acid sequence is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (CYIQNCPLG-NH2). It is a nonapeptide (nine amino acids) featuring a single intramolecular disulfide covalent bond between the cysteine residues at position 1 and position 6. This internal linkage forms a cyclic hexapeptide loop at the N-terminus, attached to an amidated tripeptide carboxyl-terminal tail.
With a molecular formula of C43H66N12O12S2 and an average monoisotopic molecular weight of 1007.19 g/mol, oxytocin relies entirely on this specific sequence and secondary cyclic loop architecture to selectively engage its target receptor. In laboratory research, maintaining sequence integrity and structural folding is vital, as modifications to any single amino acid residue drastically alter receptor affinity and biological activity.
Primary and Secondary Structure Breakdown
The primary structure of oxytocin consists of nine standard L-amino acid residues arranged in a conserved sequence: L-Cysteinyl-L-Tyrosyl-L-Isoleucyl-L-Glutaminyl-L-Asparaginyl-L-Cysteinyl-L-Prolyl-L-Leucyl-Glycinamide. The disulfide bridge between Cys1 and Cys6 imposes structural rigidity, constraining the backbone into a stable ring configuration that presents the key binding side chains outward.
The hydrophobic Tyr2 and Ile3 residues reside within the cyclic ring structure and play a central role in hydrophobic interactions with the transmembrane helices of the oxytocin receptor (OXTR). The carboxyl-terminal tail—composed of Pro7, Leu8, and Gly9-NH2—maintains flexibility while contributing to the specific electrostatic interactions required for high-affinity receptor stabilization during in vitro assays. Modification of the C-terminal amide to a free carboxylic acid significantly attenuates receptor binding, underscoring the necessity of using authentic, fully amidated research peptides in empirical protocols.
Comparative Analysis: Oxytocin, Vasopressin, and Synthetic Analogs
Oxytocin belongs to a highly conserved superfamily of neurohypophyseal peptide hormones that share high sequence homology with arginine vasopressin. A direct structural comparison highlights how minor sequence substitutions yield vastly different receptor selectivities across mammalian tissue targets.
While the oxytocin sequence is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, arginine vasopressin differs by only two amino acids, possessing a phenylalanine at position 3 and an arginine at position 8 (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2). This dual residue shift shifts primary affinity from the OXTR to the V1a, V1b, and V2 receptors. Synthetic nonapeptide derivatives, such as carbetocin, incorporate structural modifications—including a deaminated N-terminus and a thioether bridge replacing the native disulfide bond—to enhance enzymatic stability during preclinical evaluation. Researchers comparing these nonapeptide variants can reference our detailed structural guides within the research peptide library to evaluate receptor selectivity profiles.
Preclinical Mechanisms and Receptor Kinetics
In vitro models demonstrate that oxytocin acts as a full agonist at the human oxytocin receptor (OXTR), a Class A Rhodopsin-like G-protein coupled receptor (GPCR). Receptor activation triggers coupling primarily with Gαq/11 proteins, stimulating phospholipase C-beta (PLC-β) cleavage of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG).
This intracellular cascade induces rapid mobilization of ionized calcium (Ca2+) from the endoplasmic reticulum into the cytoplasm. Preclinical cell culture assays reveal that sustained exposure to native oxytocin leads to rapid receptor phosphorylation by G-protein coupled receptor kinases (GRKs), followed by beta-arrestin recruitment, receptor internalization, and transient homologous desensitization. Understanding these molecular dynamics is essential when modeling cell-line signaling trajectories or tissue contractility assays.
Preclinical Literature Findings in Rodent and Cell Models
Preclinical studies in rodent models have utilized central and peripheral administration of research-grade oxytocin to map neural pathways involved in social recognition, stress mitigation, and neuroendocrine regulation. Microinjection into specific brain regions, such as the central nucleus of the amygdala or the paraventricular nucleus (PVN) of the hypothalamus, demonstrates marked alterations in local neurotransmitter release, including GABAergic modulation.
In peripheral tissue models, isolated smooth muscle strip preparations confirm that oxytocin binding induces dose-dependent, calcium-dependent contractile responses. Animal research investigating metabolic pathways also indicates that oxytocin signaling participates in adipocyte lipolysis and systemic glucose homeostasis in rodent models of metabolic dysregulation. All such findings reflect controlled laboratory settings designed to elucidate physiological pathways.
Chemical Synthesis: Solid-Phase Peptide Synthesis (SPPS) and Folding
Producing high-purity oxytocin requires advanced Solid-Phase Peptide Synthesis (SPPS) using Fmoc (9-fluorenylmethyloxycarbonyl) protecting group chemistry. Resin-bound assembly proceeds step-wise from the C-terminal glycine residue up to the N-terminal cysteine, with specialized side-chain protecting groups ensuring regioselective assembly.
Following cleavage from the resin support using a trifluoroacetic acid (TFA) cocktail, the linear nonapeptide undergoes controlled oxidative folding to construct the critical Cys1–Cys6 disulfide bridge. Air oxidation or iodine-mediated cyclization must be precisely monitored using high-performance liquid chromatography (HPLC) to prevent improper intermolecular dimer formation or misfolded cyclic species, ensuring a homogeneous final yield.
Analytical Quality Standards: HPLC and Mass Spectrometry
To ensure reproducible data across cell-based and cell-free research applications, reagents must undergo rigorous analytical verification. Reversal-Phase High-Performance Liquid Chromatography (RP-HPLC) is utilized to measure chemical purity, verifying that the main peak accounts for ≥98% of total integrated UV absorbance, free from deletion sequences or oxidized impurities.
Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) or Electrospray Ionization Mass Spectrometry (ESI-MS) provides absolute mass verification, confirming the target theoretical molecular weight of 1007.19 Da. Every lot of oxytocin for research supplied by PX1 Research undergoes rigorous testing, with documented spectrum results provided on a lot-specific Certificate of Analysis (COA).
Endotoxin Verification and ISO 17025 Compliance
Bacterial endotoxins (lipopolysaccharides) introduce significant artifacts into cell culture, receptor binding, and tissue assays by stimulating toll-like receptor 4 (TLR4) pathways and inducing non-specific inflammatory cytokine release. Therefore, high-purity peptides intended for laboratory research must undergo stringent bioburden screening.
PX1 Research enforces strict quality control standards, screening compounds using chromogenic Limulus Amebocyte Lysate (LAL) or recombinant Factor C assays to guarantee endotoxin levels remain below strictly controlled thresholds (<0.01 EU/μg). Analytical testing is performed in ISO 17025 accredited facilities, ensuring absolute compliance and traceability for academic, biotech, and institutional accounts evaluating bulk research materials.
Laboratory Handling, Reconstitution, and Storage Protocols
Oxytocin is typically supplied as a lyophilized (freeze-dried) cake or powder. Lyophilized peptides should be stored in a sealed desiccated container at -20°C or -80°C upon arrival, shielded from light exposure, to preserve long-term chemical stability.
For reconstitution in laboratory environments, the peptide should be dissolved in sterile, bacteriostatic, or deionized water, or buffered aqueous solutions such as Phosphate-Buffered Saline (PBS, pH 7.4). Avoid high-shear mechanical vortexing, which can induce physical aggregation. Once reconstituted, stock solutions should be divided into single-use laboratory aliquots and stored at -20°C or colder to avoid repeated freeze-thaw cycles, which accelerate peptide backbone degradation.
Sourcing Verified Oxytocin Peptides for Research Applications
Selecting a reliable supplier for research-grade materials requires verifying raw material origin, facility compliance, and analytical transparency. Inconsistent peptide purity introduces unmanageable confounding variables into published experimental designs.
PX1 Research manufactures peptides in the United States using GMP-compliant facilities. Every lot is subjected to independent third-party verification, including RP-HPLC purity analysis, ESI-MS sequence mass matching, and quantitative endotoxin testing. Orders ship rapidly from our California and Arizona logistics hubs, providing research laboratories with fully documented, high-purity reagents backed by lot-traceable COAs.
Frequently Asked Questions
What is the exact amino acid sequence of oxytocin?
The primary amino acid sequence of oxytocin is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (CYIQNCPLG-NH2), characterized by a Cys1–Cys6 disulfide bond that forms a cyclic N-terminal ring attached to an amidated C-terminal tripeptide tail.
What is the molecular weight of oxytocin?
Oxytocin has a theoretical average molecular weight of approximately 1007.19 g/mol and a monoisotopic mass of 1006.44 Da.
How does oxytocin differ from vasopressin in sequence?
Oxytocin differs from arginine vasopressin at two positions: position 3 contains isoleucine in oxytocin versus phenylalanine in vasopressin, and position 8 contains leucine in oxytocin versus arginine in vasopressin.
How should lyophilized oxytocin be stored in the laboratory?
Lyophilized oxytocin should be stored at -20°C or -80°C in a desiccated, light-protected environment. Once reconstituted into liquid aliquots, store at -20°C or lower to prevent degradation and avoid repeated freeze-thaw cycles.
What solvents are recommended for reconstituting oxytocin in vitro?
Oxytocin reconstitutes readily in sterile water, 0.9% sodium chloride, or standard laboratory buffer solutions such as PBS (pH 7.4). Gentle inversion or mild swirling is recommended over vigorous mechanical vortexing.
How is oxytocin purity verified by PX1 Research?
PX1 Research verifies oxytocin lot purity via Reversal-Phase High-Performance Liquid Chromatography (RP-HPLC) to confirm ≥98% purity, Mass Spectrometry (ESI-MS/MALDI-TOF) to verify molecular mass, and LAL testing to ensure low endotoxin levels.
Why is the disulfide bond critical to oxytocin function?
The Cys1–Cys6 disulfide bond maintains the rigid cyclic ring structure required for selective binding and activation of the oxytocin receptor (OXTR). Linear or reduced oxytocin lacks biological activity.
Is oxytocin available from PX1 Research for human therapeutic use?
No. All compounds supplied by PX1 Research, including oxytocin, are strictly intended for laboratory research use only (RUO) and in vitro experimentation, and are never for human consumption, medical treatment, or clinical application.
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