511 Pyrimidines 



adenosine-5'-diphosphate (ADP), guanosine-5'-diphos- 

 phatc mannose (GDPM), adenosine-5'-triphosphate (ATP) 

 and guanosine-5'-triphosphate (GTP). 



The UTP is an intermediate in the formation of the 

 diphosphate: '• "" 



UTP + Sugar-l-phosphate ;=i UDP-Sugar + Pyrophosphate 



Once in the form of UDP esters, sugars are susceptible 

 to a variety of enzymic transformations, some of which 

 were mentioned in the section on polypeptides. For ex- 

 ample, 4-epimerization may be caused : '• '■' 



UDP-Glucose :;=± UDP-Galactose 



and 

 UDP-D-Xylose ;=± UDP-L-Arabinose 



Since there is a DPN requirement in these reactions, it 

 is likely that the 4-hydroxyl group of the sugar is oxidized 

 to a ketone, then reduced stereospecifically. Isotope work 

 supports this hypothesis.^"' ^^' ^- UDPG can be oxidized 

 also to UDP-glucuronate : '^' ^* 



2DPN 3H^ 



UDP-GIucose — ^ { >UDP-Glucuronic Acid 



H.O 2DPNH 



A yeast enzyme catalyzes the reaction : ^^- ^^ 



UDP-GIucose + Glucose-6-phosphate > Trehalose Phosphate + UDP 



Similarly, di- and polysaccharides seem to be formed 



' Paul E. Trucco, Arch. Biochem. and Biophys. 34 482 (1951). 



^ Agnete Munch-Petersen, Herman M. Kalckar, Enrico Cutolo and 

 Evelyn E. B. Smith, Nature 172 1036 (1953). 



•'Luis F. Leloir, Arch. Biochem. aiid Biophys. 33 186 (1951). 



'" Arthur Kowalsky and Daniel E. Koshland, Biochim. et Biophys. 

 Acta 22 575 (1956). 



" Laurens Anderson, Aurora M. Landel and Donald F. Diedrich, 

 ibid. 22 573 (1956). 



1- Herman M. Kalckar and Elizabeth S. Maxwell, ibid. 22 589 

 (1956). 



^■■' V. Ginsburg, E. F. Neufeld and W. Z. Hassid, Proc. Nat. Acad. 

 Sci. U. S. 42 333 (1956); V. Ginsburg, /. Biol. Chem. 232 55 (1958). 



^* Evelyn E. B. Smith, Agnete Munch-Petersen and George T. Mills, 

 Nature 172 1038 (1953). 



^^E. Cabib and Luis F. Leloir, J. Biol. Chem. 231 259 (1958). 



'•^Luis F. Leloir and E. Cabib, /. Am. Chem. Soc. 75 5445 (1953). 



