310 JOHN M. BUCHANAN 







H ? C — NH, H ? C — NH 



I I \ 



-X n-^C CHO 



0IP0CH 2 NH 0=POCH NH 



OH OH OH OH 



Fig. 4. Structures of glycinamide ribonucleotide and formylglycinamide ribo- 

 nucleotide. 



class of enzymes called nucleotide pyrophosphorylases. 3537 A nucleotide 

 phosphorylase has been isolated which utilizes the bases hypoxanthine, 

 guanine, and 6-mercaptopurine 38 and is different from another enzyme of 

 the same class which reacts adenine and 5-amino-4-imidazolecarboxamide. 39 

 Still other nucleotide pyrophosphorylases are involved in the synthesis of 

 the pyrimidine nucleotides. 36 ■ 40 



5-Phosphoribosylpyrophosphate is a reagent of great versatility in the 

 enzymic reactions concerned with the synthesis of phosphoribosyl com- 

 pounds. Of considerable interest is the fact that it is also involved in the 

 synthesis of glycinamide ribonucleotide from glycine. 27 An enzyme 4142 

 5-phosphoribosylpyrophosphate amidotransferase has been isolated from 

 avian liver which catalyzes the reaction of 5-phosphoribosylpyrophosphate 

 with glutamine to yield 5-phosphoribosylamine, glutamic acid, and inor- 

 ganic pyrophosphate according to Eq. (2). Although 5-phosphoribosyl- 



5-Phosphoribosylpyrophosphate + glutamine + H 2 -+ 



5-phosphoribosylamine + glutamic acid + pyrophosphate 



amine is presumed to be the product of Eq. (2), it has not been isolated so 

 far because of its chemical instability. Incubation of the purified enzyme 

 with P 32 -labeled pyrophosphate or with C 14 -labeled glutamic acid and other 

 participants of the reaction does not lead to the formation of radioactive 

 5-phosphoribosylpyrophosphate or glutamine. These experiments are taken 

 as evidence of the essential irreversibility of the reaction. There is evidence 

 that an inversion of the configuration at position 1 of the ribose takes place 



36 C. N. Remy, W. T. Remy, and J. M. Buchanan, J. Biol. Chem. 217, 885 (1955). 



36 I. Lieberman, A. Romberg, and E. S. Simms, J. Biol. Chem. 215, 403 (1955). 



37 A. Romberg, I. Lieberman, and E. S. Simms, J. Biol. Chem. 215, 417 (1955). 



38 L. N. Lukens and R. A. Herrington, Biochim. et Biophys. Acta 24, 432 (1957). 



39 J. G. Flaks, M. J. Erwin, and J. M. Buchanan, /. Biol. Chem. 228, 201 (1958). 



40 I. Crawford, A. Romberg, and E. S. Simms, J. Biol. Chem. 226, 1093 (1957). 



41 D. A. Goldthwait, J. Biol. Chem. 222, 1051 (1956). 



42 S. C. Hartman and J. M. Buchanan, J. Biol. Chem. 233, 451 (1958). 



