Disulfide bridges in peptides
Last reviewed 2026-10-10 · Sable Peptides · Research use only
Sable research method explainer. Updated 2026-10-10. Research use only.
Short answer
A disulfide bridge is a covalent S-S bond between the thiol groups of two cysteine residues. It can link two parts of one chain, closing a ring, or link two separate chains. Disulfides lock a peptide into a narrower set of shapes and are central to the structure of many natural peptides. Góngora-Benítez, Tulla-Puche and Albericio review their chemistry and roles in detail (Góngora-Benítez et al., 2014).
Examples on the reference pages
Oxytocin, Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, has a disulfide between Cys1 and Cys6. This closes a six-residue ring, followed by a three-residue tail.
AOD-9604 is a 16-residue modified growth-hormone fragment with one disulfide bridge.
Larger proteins listed on the reference pages, such as IGF-1 LR3, contain several disulfides that must pair correctly to give the folded structure.
Formation and mass
A disulfide forms by oxidation: two thiols (-SH) lose a hydrogen atom each and join. The oxidised peptide is therefore about 2.016 g/mol lighter than the reduced, open form. Mass spectrometry easily distinguishes the two, and this is one of the checks behind an identity result on a certificate of analysis. PubChem formulas, such as oxytocin's C43H66N12O12S2, describe the oxidised, bridged form.
How disulfides are made in synthesis
The linear chain is assembled by solid-phase synthesis with the cysteine thiols protected. After cleavage, the peptide is oxidised in dilute solution, by air, dimethyl sulfoxide, iodine or other oxidants, so that the intramolecular bridge forms in preference to intermolecular dimers. For peptides with two or more disulfides, chemists use orthogonal cysteine protecting groups and open them one pair at a time, so that each bridge forms between the intended residues (Góngora-Benítez et al., 2014).
Why the bridge matters structurally
A disulfide holds two parts of the chain close together, whatever the surrounding sequence would otherwise do. In a small ring such as oxytocin's, this fixes the relative positions of the residues inside the ring and restricts the tail. In larger peptides and proteins, several bridges together define the folded shape, which is why correct pairing is part of identity and not just a detail of synthesis.
Typical impurities
- Reduced (open) form: about 2 Da heavier, often at a different HPLC retention time.
- Dimers and oligomers formed between chains: roughly double the mass.
- Mispaired isomers in multi-disulfide peptides: the same mass as the correct product but a different HPLC retention time. HPLC and mass identity are needed together to rule these out.
Handling notes for the lab
- Reducing agents such as dithiothreitol, beta-mercaptoethanol and TCEP break disulfides, so check buffer compatibility before use.
- Free thiols and basic pH can promote disulfide exchange (scrambling). Keep conditions in line with your SOP.
- Store lyophilised material sealed and dry, as for other peptides, and record the lot number against each experiment.
At Sable
The /ref structure text states where a disulfide is present, and formulas are given for the bridged form. Batches are released at ≥99% purity by HPLC with identity checked against the expected mass. Certificates are available for every lot at /coa. Sable Peptides has been operating since 2019 and supplies every compound mentioned here as laboratory research material only. Nothing on this page is advice on use in people or animals, and no administration or medical-use information is provided.
Key terms
- Thiol
- An -SH group, as on the cysteine side chain.
- Oxidation (here)
- Removal of hydrogen atoms from two thiols so that they join as -S-S-.
- Reduction
- The reverse reaction, which breaks a disulfide back into two thiols.
- Disulfide scrambling
- Rearrangement of disulfide pairings, which gives isomers of identical mass.
- TCEP
- Tris(2-carboxyethyl)phosphine, a thiol-free reducing agent.
Common questions
How much lighter is the oxidised form?
About 2.016 g/mol, the mass of two hydrogen atoms.
Which Sable compounds contain a disulfide?
Examples include oxytocin (Cys1 to Cys6) and AOD-9604.
What breaks a disulfide?
Reducing agents such as DTT, beta-mercaptoethanol or TCEP.
Related explainers
- Cyclic vs linear peptides: what ring closure changes
- Monoisotopic vs average mass: reading peptide mass data
Related reference pages
Sources
- Góngora-Benítez M, Tulla-Puche J, Albericio F. Multifaceted roles of disulfide bonds. Peptides as therapeutics. Chem Rev. 2014;114(2):901-926. https://doi.org/10.1021/cr400031z
- Zorzi A, Deyle K, Heinis C. Cyclic peptide therapeutics: past, present and future. Curr Opin Chem Biol. 2017;38:24-29. https://doi.org/10.1016/j.cbpa.2017.02.006
- Jones J. Amino Acid and Peptide Synthesis. Oxford Chemistry Primers. Oxford University Press; 2002. https://doi.org/10.1093/hesc/9780199257386.001.0001
Questions
How much lighter is the oxidised form?
About 2.016 g/mol, the mass of two hydrogen atoms.
Which Sable compounds contain a disulfide?
Examples include oxytocin (Cys1 to Cys6) and AOD-9604.
What breaks a disulfide?
Reducing agents such as DTT, beta-mercaptoethanol or TCEP.
Sources
CoA for every lot — request yours and we email it within 2 hours.
Research use only. Not for human or veterinary use. No health claims.