Disulphide bond

A disulphide bond is a covalent S-S bond formed between the sulphur atoms of two cysteine side chains. Disulphides are the strongest non-backbone bonds in peptide / protein structure and dramatically stabilise tertiary fold. Many endogenous peptides depend on disulphide bonds for activity — insulin (3 disulphides), oxytocin (1 disulphide), and somatostatin (1 disulphide). Reduction of disulphide bonds (e.g. by DTT or β-mercaptoethanol) destroys the peptide's bioactivity. Research peptides containing cysteines are typically synthesised with disulphide formation as a final step.