Disulphide bond

A disulphide bond is a covalent linkage between two sulfhydryl groups on the R groups of two cysteine residues on a polypeptide backbone. It can either be a inter or intra molecular bond. This type of linkage forms during the processing of the protein in the rough endoplasmic reticulum. The disulphide bond is responsable for the stability of the tertiary and quaternary structure of a majority of known proteins.

References 

• Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2008). Molecular Biology of the Cell. New York. Garland Science