Figure 1. Proglucagon expression in α cells. Alternative cleavages of proglucagon to glucagon and GLP-1. The relative levels of expression of the pro-hormone covertases PC2 and PC1/3 determine the production of glucagon or GLP-1, respectively. Glucagon is a metabolic (gluconeogenic) hormone produced in fully differentiated α-cells and GLP-1 is both an insulinotropic (insulin-releasing) hormone and a growth and survival peptide produced in undifferentiated pro-α-cells. GRPP, glucagon-related polypeptide. GLP-2, glucagon-like peptide-2 involved in intestinal growth.