The U16-850 monoclonal antibody specifically binds to glucagon, a member of the secretin family of active peptides. Glucagon is an evolutionarily conserved peptide hormone that participates in the regulation of carbohydrate metabolism by counteracting the effects of insulin. Glucagon is produced by α cells in the islets of Langerhans of the pancreas. The CGC gene encodes the precursor molecule preproglucagon, which is cleaved to form proglucagon that is in turn cleaved to form at least four distinct peptides, including glucagon, in different tissues. Hypoglycemia causes the secretion of glucagon, which binds to the class B G-protein-coupled glucagon receptor that is mainly expressed in liver and kidney, causing reduced glycogenesis and glycolysis and increased glycogenolysis and gluconeogenesis. The expression of glucagon can be used to monitor the pancreatic differentiation of pluripotent stem cells.