36 



W. G. OVEREND AND M. STAGEY 



TABLE VI 

 Rf Values of Pentose Phosphates 



separated by ion exchange with the use of the borate complex, ^*^' '^° and 

 it is also possible that paper ionophoresis can be used. [Compare Chapter 8.] 

 (1) Ribose-1 -phosphate. Kalckar"''- '^i-i^^ discovered that enzymic phos- 

 phorolysis of some nucleosides (inosine, guanosine) leads to the production 

 of a pentose phosphate, isolable as its barium salt, which is most probably 

 D-ribose-1 -phosphate. [Cf. Schlenk, Chapter 24.] The yield of pentose phos- 

 phate generally was low (i.e., 7-10 mg. of the barium salt from 40-60 mg. 

 of inosine). Probably losses are due to acid hydrolysis, to nonspecific and 

 specific contaminant phosphatase action during the incubation with the 

 enzyme and to retention on the bulky barium phosphate precipitate during 

 the working up stage. Moreover the position of the equilibrium favors the 

 formation of hypoxanthine riboside. Although Kalckar'^^ was unable to 

 demonstrate that adenosine or xanthosine or the pyrimidine ribosides 

 would act in the system, it appears that the following relation might 

 hold true: 



Ribose-1-purine + PO4 ^ Ribose-1 -phosphate -t- purine 



Subsequent work has demonstrated that in addition to the examples stud- 

 ied by Kalckar mammalian purine nucleoside phosphorylase catalyzes the 

 synthesis from the respective base and ribose-1 -phosphate of xanthosine, >^* 

 8-azaguanine riboside, '^^ nicotinamide riboside'^''' and 4-amino-5-imidazole- 



•89 J. X. Khym and W. E. Cohn, /. Ain. Chem. Soc. 75, 1153 (1953). 



190 J. X. Khym, D. G. Doherty, E. Volkin, and W. E. Cohn, J. Ajh. Chem. Soc. 75, 



1262 (1953). 

 '9' H. M. Kalckar, Federation Proc. 4, 248 (1945). 

 192 H. M. Kalckar, J. Biol. Chem. 158, 723 (1945). 

 '93 H. M. Kalckar, Symposia Soc. Exptl. Biol. 1, 38 (1947). 

 '94 H. M. Kalckar, Biochim. et Biophys. Ada 4, 232 (1950). 

 196 M. Friedkin, J. Am. Chem. Soc. 74, 112 (1952). 

 196 M. Friedkin, Federation Proc. 11, 216 (1952). 

 19V J, W. Rowen and A. Kornberg, J. Biol. Chem. 193, 497 (1951). 



