Insulin is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the INS gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism of carbohydrates, fats and protein by promoting the absorption of glucose from the blood into liver, fat and skeletal muscle cells. Proinsulin is cleaved into insulin and C-peptide. The two are stored in the secretory granules of the pancreatic β-cells and eventually released together in equimolar amounts. C-peptide has an important role in facilitating the correct folding of insulin and formation of its disulfide bridges.