336 r. SCHLENK 



reactions are remote from the ring assembly by several steps; hence 'their 

 discussion will be omitted. 



3. p-Aminobenzoic Acid and Folic Acid 



An obvious function of p-aminobenzoic acid and folic acid in purine and 

 pyrimidine metabolism is to serve as part of the structure of citrovorum 

 factor. There are numerous experimental results pointing to this relation- 

 ship ; in most instances fastidious bacteria or organisms with an antagonist- 

 induced deficiency have been used, but no in vitro observations permitting 

 exact formulations have been made. Since numerous reviews on this sub- 

 ject are available, a discussion will be omitted.^* '^-^"^^^ 



VI. Addendum 



Nucleoside-5' -triphosphates 



The most significant recent development is the isolation of various 

 ribonucleoside-5'-triphosphates. These compounds may occupy a key posi- 

 tion in future concepts of polynucleotide synthesis. Guanosine-5'-triphos- 

 phate and uridine-5'-triphosphate were obtained from rabbit muscle;"^ the 

 concentration was 2 to 4 % of that of the ATP fraction. Yeast appears to be 

 a good source of uridine-5'-triphosphate.'^^ All of the ribonucleoside tri- 

 phosphates were found in tumor and other tissues. ^^*'^'^ The occurrence of 

 deoxyadenosine diphosphate and triphosphate in muscle and kidney has 

 been suggested. '^^ 



The studies of Kalckar and his co-wojkers'^^'^^^ have revealed important 

 information about the function and biogenesis of ribonucleotide triphos- 

 phates.'*^'*'^ The following enzymic reactions were observed: 



Uridine triphosphate + adenosine diphosphate :^ uridine diphosphate ,^., 



+ adenosine triphosphate 



'2^ W. Shive, Vitamins and Hormones 9, 76 (1951) 

 "0 T. H. Jukes, Federation Proc. 12, 633 (1953). 

 "1 J. R. Totter, J. Cellular Comp. Physiol. 41, Suppl. 1, 241 (1953). 

 "3 R. Bergkvist and A. Deutsch, Acta Chem. Scand. 7, 1307 (1953). 

 "^ S. H. Lipton, S. A. Morell, A. Frieden, and R. M. Bock, J. Am. Chem. Soc. 75, 

 5449 (1953). 



135 R. B. Hurlbert, H. Schmitz, A. F. Brumm, and V. R. Potter, J. Biol. Chem. 209, 

 23 (1954) ;H. Schmitz, R. B. Hurlbert, and V. R. Potter, ibid. 209, 41 (1954); L. 

 Hecht, V. R. Potter, and E. Herbert, Biochim. et Biophys. Acta 15, 134 (1954). 



136 J. Sacks, L. Lutwak, and P. D. Hurley, /. Am. Chem. Soc. 76, 424 (1954). 



1" H. Z. Sable, P. B. Wilber, A. E. Cohen, and M. R. Kane, Biochim. et Biophys 



Acta 13, 156 (1954). 

 138 H. M. Kalckar, Biochim. et Biophys. Acta 12, 250 (1953). 

 1" A. Munch-Petersen, H. M. Kalckar, E. Cutolo, and E. E. B. Smith, Nature 172, 



1036 (1953); H. M. Kalckar, Science 119, 479 (1954). 

 135=' I. Lieberman, A. Kornberg, and E. S. Simms, /. Ain. Chem. Soc.76, 3608 (1954). 

 i"*' J. L. Strominger, L. A. Heppel, and E. S. Maxwell, Arch. Biochem. and Biophys. 



52, 488 (1954). 



