CHEMISTRY OF NUCLEOSIDES AND NUCLEOTIDES 165 



for giianosine-5'-phosphate, and its identity with synthetic cytidine-5'- 

 phosphate has been established. 



e. Uridine-5' -phosphate (XXV) 



Although uridine-5'-phosphate may be formed by enzymic hydrolysis of 

 ribonucleic acid'^^ it is also present as a structural unit in the uridme di- 

 phosphate coenzymes. It is hydrolyzed either enzymically or chemically to 

 uridine and consumes 1 mol. periodate, so it must be a 5'-phosphate. 

 It is identical with synthetic uridine-5'-phosphate. 



-0- 



OH OH 



CH-CH-CH-CH-CH.-OPOjH^ 



I 



N^ 

 OH 



XXV 



Uridine-5'-phosphate 



/ Adenylic Acids a and b 



When ribonucleic acid is subjected to cautious hydrolysis, a material 

 known as "yeast adenylic acid" is obtained, together with other nucleotides 

 and nucleosides.!" • 1^^' ^"^ The early workers considered that this was a 

 single substance, but recent work has shown that two isomeric adenylic 

 acids (a and h) are formed by hydrolysis of ribonucleic acid, and it is not 

 quite certain which isomer was under investigation at each stage of the 

 initial structural work. In fact, it is probable that both isomers were present 

 on some occasions. For these reasons, and also because of the ready inter- 

 conversion of the isomers under mild acid conditions, the early work on the 

 location of the phosphate group in yeast adenylic acid is unreliable. How- 

 ever, it was clear that yeast adenylic acid is a monophosphate (or mixture 

 of monophosphates) of adenosine, since it yields adenosine and phosphoric 

 acid in equal amounts on hydrolysis in ammonia.i^^ Furthermore, the phos- 

 phate group must be situated on the sugar residue, since after treatment 

 with nitrous acid it gives an inosine phosphate which hydrolyzes readily to 

 hypoxanthine and a ribose phosphate (or mixture of ribose phosphates). i«« 

 This "ribose phosphate" differs from ribose-5-phosphate. It would appear, 

 then, that yeast adenylic acid is adenosine-2'- or adenosine-3'-phosphate 

 (XXVI, XXVII). The ribose phosphate obtained from yeast adenylic acid 



i«3 A. C. Paladini and L. F. Leioir, Biochem. J. 51, 426 (1952). 

 1" W. Jones and R. P. Kennedy, J. Pharmacol. 13, 45 (1919). 

 166 S. J. Thannhauser, Z. physiol. Chem. 107, 157 (1919). 

 166 p. A. Levene and S. A. Harris, J. Biol. Chem. 101, 419 (1933). 



