A protein hormone, secreted by the β‎ (or B) cells of the islets of Langerhans in the pancreas, that promotes the uptake and metabolism of glucose by body cells, and thereby controls its concentration in the blood. Following a meal, and the consequent rise in blood glucose concentration, insulin secretion enhances energy metabolism, prompts liver cells to convert excess glucose to the storage carbohydrate glycogen, and in adipose tissue promotes fat synthesis from glucose. Then, as glucose levels fall, so does insulin secretion. However, if blood glucose falls markedly, the pancreas secretes glucagon, a hormone that counteracts the effects of insulin. Underproduction of insulin results in the accumulation of large amounts of glucose in the blood (hyperglycaemia) and its subsequent excretion in the urine in abnormally high concentrations (glycosuria). This condition, known as diabetes mellitus, can be treated successfully. Type 2, or non-insulin-dependent, diabetes mellitus is caused by failure of target cells to respond to insulin; it can generally be treated by diet alone. Type 1, or insulin-dependent, diabetes mellitus is an autoimmune disease in which the β‎ cells of the pancreas are destroyed; it is more severe and requires treatment by insulin injections. Insulin was the first protein whose amino-acid sequence was fully determined (in 1955). Therapeutic human insulin is now manufactured using recombinant human DNA in cultured bacteria or yeast cells.