A plasma protein produced by the liver that maintains fluid balance in the blood and transports fatty acids in the plasma and interstitial fluid. It is the most abundant protein in human serum, and one of the first discovered and earliest studied proteins. Serum albumin was precipitated from urine in 1500 by Paracelsus, and was crystallized in 1894 by A. Gürber. Probably no other protein has been studied as extensively as serum albumin, and our knowledge of its structure and interactions with its ligands has come from many researchers, using a great variety of experimental approaches. Its ability to bind many different ligands, most of which are hydrophobic anions, and several molecules of the same ligand (fatty acid) is well documented. Fatty acids, bilirubin (an orange-yellow bile pigment formed in the breakdown of red blood cells), and hematin (a blue to blackish-brown compound formed in the decomposition of hemoglobin) represent the endogenous ligands of albumin with highest affinity.