The biosynthesis of pentoses and their incorporation into mononucleotides 



least two enzymes which could be separated by alcohol fractionation. The first 

 enzyme reaction consisted in a reaction between ribose-5-phosphate and adenosine 

 triphosphate to yield an activated ribose phosphate ester. 



In Dr. Kalckar's laboratory similar observations have been made. Adenine is 

 known to be incorporated into the nucleic acids on a large scale (Brown, 1948), and 

 Goldwasser (1953) found that in pigeon-liver extract 14 C-labelled adenine is 

 incorporated into adenosine monophosphate, adenosine diphosphates and adenosine 

 triphosphates at an appreciable rate. Saffran and Scarano (1953) working with the 



^265 \ 



800 



700 

 600 

 500 

 WO 

 300 

 200 

 WO 





**-*x-x— x . 



'X+AZP022/S/V 



\ 



••+, 



ATP 0.22/jM+R5P3/jM 







to 



20 



30 



w SO 



60 m/n. 



Figure 3. Phosphorylation of ribose-yphosphate with adenosine-triphosphate. 



The reference cuvette contained 0-22 /*m adenosine triphosphate in 3 ml., and 

 the spectrophotometer was brought to zero at an optical density of 0*5. The 

 experimental cuvettes contained 0-39 him potassium chloride, 0-03 mM magnes- 

 ium chloride, 0-045 him dipotassium hydrogen phosphate, 5-adenylate kinase 

 207- of protein per ml., 5-adenylate deaminase 25?- of protein per ml., total 

 volume 3-19 ml., pH 6-8. At o min. no?- of protein per ml. of 5-phospho- 

 ribokinase was added to the experimental cuvettes 



Abscissa: time in minutes; ordinate: extinction X io 3 at 265 rru*. From Scarano 

 (1953)- 



same system found that here also the presence of ribose-5-phosphate and adenosine 

 triphosphate stimulated the incorporation of adenine into adenosine monophosphate. 

 They found furthermore that in the dialysed extract the incorporation was com- 

 pletely dependent on both of these two compounds (Table III). In this system ribose- 

 5-phosphate could, however, be replaced by ribose- 1 -phosphate, whereas ribose-2- 

 phosphate and ribose-3-phosphate were inactive. In addition they were able to 

 demonstrate that this reaction also proceeds in at least two steps, the first one being 

 an activation of ribose phosphate with adenosine triphosphate, and the second one 

 being the reaction between this activated compound and adenine to form the 

 5 / -adenylic acid. 



73 



