The protein encoded by the human proglucagon (GCG) gene is processed after translation into several polypeptides, each of which undergoes further modification. Two of these polypeptides constitute the biologically active forms of glucagon-like polypeptide 1 (GLP-1): GLP-1-(7-36)NH2 and GLP-1-(7-37). These active forms have a short half-life in the blood and are rapidly degraded by dipeptidyl peptidase 4 (DPP-4) into the inactive forms: GLP-1-(9-36)NH2 and GLP-1-(9-37).
GLP-1 is produced mostly in the intestinal L cells. It is a potent stimulator of glucose-dependent insulin secretion and a suppressor of plasma glucagon levels. Additional roles for GLP-1 have been proposed, including inhibition of gastric cell motility and secretion, stimulation of pancreatic beta cell proliferation, and inhibition of pancreatic beta cell apoptosis. The GLP-1 ELISA kits are solid-phase sandwich ELISAs that use two highly specific antibodies to either the active or inactive forms of human GLP-1.