(1) The single covalent bond formed from the coupling of thiol groups, especially of cysteine residues.
(2) The linkage formed by the oxidation of two SH groups, each attached to a cysteine, stabilizing the structure of many protein molecules (during protein synthesis).
Disulphide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium.
Below is an example of a disulphide bond:
Cysteine---SH + HS---Cysteine → Cysteine---S-S---Cysteine + 2H+ + 2e-
Two cysteines linked by a disulphide bond forms a cystine.
Variant: disulfide bond