Insulin is a relatively simple protein consisting of 51 amino acids arranged as two polypeptide chains, an α- chain and β-chain, connected by disulfide bonds.
Two-chain polypeptide hormone produced by the β-cells of pancreatic islets. Its molecular weight is ~5800 Da. The α and β chains are joined by two interchain disulfide bonds. The α chain contains an intrachain disulfide bond.