529 



Purines 



CN 



>f< 



CN 



° r "'"^ 



0<-P— O— P— O— CH . 



I I 



OH OH 



OH 



Guanosine Diphosphate 



Factor B 



(Factor B = Vitamin B12 



minus the 



dimethylbenzimidazole 



nucleotide moiety) 



OH OH 



This substance has been suggested as an intermediate 

 near the end of the vitamin B12 synthesis just prior to 

 introduction of the dimethylbenzimidazole nucleotide. 



There is evidence that labeled guanine is an isotopic 

 precursor of riboflavin in Eremothecium ashbyii. Ade- 

 nine also is a precursor of this vitamin. In each case 

 the Cs atom is lost. In the case of adenine, at least, the 

 pyrimidine ring is incorporated intact into riboflavin^* 

 although pyrimidines such as uracil and thymine are in- 

 effective precursors." 



Inosine is an intermediate in the biosynthesis of ade- 

 nine and guanine, but beyond the phosphoenol pyruvate 

 formation and some of the less specific reactions of the 

 purine nucleotides (phosphate transfer, etc.) few func- 

 tions have been discovered. 



The purine nucleotides have been reviewed.^" ^^' ^*- ^^- ^°- ^^ 



i-* Walter S. McNutt, Jr., /. Biol. Chem. 219 365 (1956). 



15 John A. MacLaren, /. Bacteriol. 63 233 (1952). 



1'' Paul D. Boyer, Henry Lardy and Karl Myrback, "The Enzymes" 

 Vol. II, Robert M. Bock, Adenine nucleotides and properties of pyro- 

 phosphate compounds. Academic Press, New York, 1960, pp. 3-27. 



1" Ibid., Merton F. Utter, Guanosine and inosine nucleotides, pp. 

 75-87. 



18 Jack L. Strominger, Physiol. Rev. 40 55-111 (1960). 



"J. Baddiley and J. G. Buchanan, Quart. Rev. 12 152-172 (1958). 



-° Standish C. Hartman and John M. Buchanan, Advances in En- 

 zymology 21 199-261 (1959). (Copyright 1959 by Interscience 

 Publishers, Inc., New York) 



21 G. E. W. Wolstenholme and Cecilia M. O'Connor (Eds.), "CIBA 

 Foundation Symposium on the Chemistry and Biology of Purines," 

 J. M. Buchanan, J. G. Flaks, L. C. Hartman, B. Levenberg, L. N. 

 Lukens and L. Warren, The enzymatic synthesis of inosinic acid 

 de novo. Little, Brown and Co., Boston, 1957, pp. 233-255. 



