Can be isolated from calf's liver, thymus, and yeast. The commercial product is derived from yeast. Pentose nucleic acids (isolated from yeast) are digested with rattlesnake venom (freed of 5′-monoesterase) and the nucleotides are separated by chromatography: Cohn, Volkin, Arch. Biochem. Biophys. 35, 465 (1952); J. Biol. Chem. 203, 319 (1953). For alternate procedures see the refs under Uridine Diphosphate Glucose. Syntheses: Chambers, J. Am. Chem. Soc. 81, 3032 (1959); Moffatt, Khorana, ibid. 83, 649 (1961).