Uridine diphosphate pentoses

Uridine 5 -Diphosphate. Uridine 5. (trihydrogen diphosphate) UDP uridine 5 -pyrophosphate uridine-5-pyrophosphoric acid. C9HI4N20,jPj mol wt 404.18. C 26.75%, H 3.49%, N 6.93%, O 47.50%, P 15.33%. Can be isolated from calf s fiver, thymus, and yeast. The commer -cial 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 (19S3). 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). 

Reactions (2) and (3) would be similar to those leading to the formation and transformation of cytosine diphosphate-choline 106) or uridine diphosphate 107). It is conceivable, of course, that the reduction of the pento l group to ribityl does not occur with the free pentose phosphate as pictured [reaction (1)], but by a mechanism involving the conversion of a cystosine diphosphate-pentose to cytorine diphosphate-ribitol. This type of reaction would be distantly related to reactions such as the oxidation of uridine diphosphate-glucose to uridine diphosphate-glucuronic acid 108,109). 

Biochemical epimerizcUum at certain asymmetric centers has been discovered relatively recently. An example is glucose galactose the coenzyme is uridine diphosphate, whose reactions will be discussed in another context (cf. Chapt. XVII-4). Among the pentoses, there is the conversion of ribvilose 5-phosphate to xylulose 5-phosphate (epimerization at C-3). 

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