For many proteins and peptides, disulfide bridges are prerequisite for their proper biological function. Many commercialized proteins are cross-linked by disulfide bridges that increase their resistance to destructive effects of extreme environment used in industrial processes or protect protein-based therapeutics from rapid proteolytic degradation. Manufacturing of these products must take into account oxidative refolding—a formation of native disulfide bonds by specific pairs of cysteines located throughout a sequence of linear protein.

Disulfide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium. Since most cellular compartments are reducing environments, in general, disulfide bonds are unstable in the cytosol, with some exceptions as noted below, unless a sulfhydryl oxidase is present.

Cystine is composed of two cysteines linked by a disulfide bond, disulfide bonds in proteins are formed between the thiol groups of cysteine residues by the process of oxidative folding. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. The prototype of a protein disulfide bond is the two-amino-acid peptide cystine, which is composed of two cysteine amino acids joined by a disulfide bond.