Two-chain polypeptide hormone produced by the Î²-cells of pancreatic islets. Its molecular weight is ~5800 Da. The Î± and Î² chains are joined by two interchain disulfide bonds. The Î± chain contains an intrachain disulfide bond. Insulin regulates the cellular uptake, utilization, and storage of glucose, amino acids, and fatty acids and inhibits the breakdown of glycogen, protein, and fat.