Source:http://linkedlifedata.com/resource/umls/id/C1511122
NCI: Many different peptides act as signaling molecules, including the proinflammatory peptide bradykinin, the protease enzyme thrombin, and the blood pressure regulating peptide angiotensin. While these three proteins are distinct in their sequence and physiology, and act through different cell surface receptors, they share in a common class of cell surface receptors called G-protein coupled receptors (GPCRs). Other polypeptide ligands of GPCRs include vasopressin, oxytocin, somatostatin, neuropeptide Y, GnRH, luteinizing hormone, follicle stimulating hormone, parathyroid hormone, orexins, urotensin II, endorphins, enkephalins, and many others. GPCRs form a broad and diverse gene family that responds not only to peptide ligands but also small molecule neurotransmitters (acetylcholine, dopamine, serotonin and adrenaline), light, odorants, taste, lipids, nucleotides, and ions. The main signaling mechanism used by GPCRs is to interact with G-protein GTPase proteins coupled to downstream second messenger systems