140 NITROGEN METABOLISM 



ribose- 5 -phosphate may likewise be synthesized from 

 phosphoglyceraldehyde and glycolaldehyde, Esch. colt and 

 Sac. cerevisiae are known to be capable of performing 

 the series of reactions, glucose — > glucose-6-phosphate — >- 

 6-phosphogluconate — > 3(2)-ketogluconic acid — > ribulose- 

 5-phosphate — > ribose-5-phosphate — > ribose- 1 -phosphate 

 [22, 36]. In view of the reversible nature of the nucleosidases, 

 it is reasonable to suggest that transfer reactions between 

 the pentose- 1 -phosphates and purines or pyrimidines are a 

 possible route of nucleoside synthesis. There is, however, 

 no proof that this is the natural pathway and mention has 

 already been made of some evidence, admittedly indirect, 

 which indicates that glycosidation precedes completion of 

 the heterocylic rings present in purines and pyrimidines. 

 With regard to the phosphorylation of nucleosides to form 

 nucleotides, all of our present knowledge concerns nucleo- 

 tides known to be constituents of coenzymes rather than of 

 nucleic acids. The following syntheses, catalysed by enzyme 

 preparations obtained from yeast {c, d, f) and from liver 

 \e, g) have been described [24, 46]: 



(c) adenosine+ATP — > adenosine-5-phosphate+ADP 



Id) riboflavin+ATP — > FMN+ADP 



{e) nicotinamide-riboside+ATP — >■ 



nicotinamide-riboside-5-phosphate+ADP 

 (/) FMN+ATP — > FADN+pyrophosphate 



(^) Nicotinamide-riboside-5-phosphate+ATP — > 



DPN +pyrophosphate 



Effect of bacteriophage on nucleic acid metabolism of host 

 cell [17] 

 All viruses consist essentially of nucleic acids and pro- 

 teins, and, in addition, the more complex types infecting 

 animals also contain fatty material. Deoxypentose nucleic 

 acids and PNA are found respectively in bacteriophages and 

 plant viruses, and although most animal viruses contain only 

 one type of nucleic acid, a few, e.g. the influenza virus, 

 appear to contain both DPNA and PNA. When purified 

 fully infective preparations of various viruses have been 

 examined for the presence of known enzymes, no activity 



