Glucagon is an endocrine hormone that helps to control blood sugar levels. Glugacon is the "opposite" of the better known insulin. While insulin reduces the level of glucose in the blood glucagon increases it. Both glucagon and insulin are secreted in the islets of Langerhans in the pancreas. Glucagon is produced by the alpha cells in these islets.

Glucagon is a short hormone, its peptide chain being made up of only 29 amino acids. In solid form it looks like a white powder.
Molecular mass: 3483
Empirical Formula:C153H225N43O49S

Role in the Body
When blood glucose levels are too low alpha cells in the islets of Langerhans produce proglucagon, which is processed into glucagon and released. This glucagon is carried through the bloodstream and when it interacts with liver cells causes them to break down glycogen to glucose. Glycogen is normally stored within the liver. It provides a source of energy that can be acessed much more quickly than that of fat. As glycogen is broken down the level of glucose in the blood increases, and the secretion of glycogen ceases. Glucagon also encourages the breakdown of fats, and their increased use within the body.

Glycogen production is also stimulated by eating a lot of protein. This is why there are some high-protein diets that are supposedly effective. If glucagon secretion remains high then less of the energy taken in in food should be stored as fat or glycogen.

Glucagon and the Diabetic
Glucagon is not needed in the daily regime of diabetics, but should be available in case of emergency hypoglycemia. If a diabetic falls unconscious it isn't possible to raise their blood-sugar level by feeding them, so unless an intravenous drip is available then an injection of glucagon is the only way to quickly raise this level and prevent brain damage or death. The glucagon in these kits is produced by transgenic Escherichia coli bacteria.

Biology 2
Collins Medical dictionary