Pendetide (GYK-DTPA) is a chelating agent. It consists of pentetic acid (DTPA) linked to the tripeptide glycine (G) – L-tyrosine (Y) – L-lysine (K). Chelation is the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central atom. Usually these ligands are organic compounds, and are called chelants, chelators, chelating agents, or sequestering agents. The ligand forms a chelate complex with the substrate. Chelate complexes are contrasted with coordination complexes composed of monodentate ligands, which form only one bond with the central atom.