Insulin is a polypeptide hormone synthesized by the beta cells of the Islets of Langerhans within the pancreas. Insulin stimulates the cells of the body to take up glucose for cellular metabolism and storage. People who have an insulin deficiency develop the disease diabetes. Suffers either manifest insulin insensitivity where cells are rendered unresponsive to the hormone, or autoimmune destruction of the beta cells leading to decreased secretion of insulin.
Insulin that is administered in the treatment of diabetes is now made biosynthetically by a genetically modified, non-disease producing strain of Escherichia coli bacteria. This method creates an insulin with relatively few impurities compared to the old method of extraction from bovine (cow) or porcine (pig) pancreas, although high-pressure liquid chromatography (HPLC) methods ensure that all forms of insulin reach a high level of purity.