Disulphide bonds

A disulphide bond (also known as S-S bonds, disuphide bridges and disulfide bonds) is a covalent bond between two sulphur atoms.

The general equation for the formation of a disulphide bond:

2 R-SH ⇔  R-S-S-R + 2H⁺ + 2e^-

(Note: "R" represents a side chain)

They are the most common cross-linkage found in polypeptides. Disulphide bonds can form by oxidation, between the thiol (-SH) groups on two adjacent cysteine residues.The cysteine residues may be on the same polypeptide chain (an intrachain disulphide bond) or on two separate polypeptide chains (an interchain disulphide bond). Disulphide bonds are an important structural characteristic of polypeptides, providing stability to the protein because only large amounts of energy are able to break the covalent cross-link. Reinforcement of the polypeptide conformation is provided by the disufide bond in order for the protein to maintain its structure (and hence function) in extracellular conditions. Proteins to do not require the additional support inside the cell, the reducing environment of cytosol converts a disulphide bond back to thiol groups by reducing agents.