BIOSYNTHESIS OF PENTOSES 261 



creased.^" This may be interpreted as a diversion of glucose utilization from 

 the oxidative pathway to the glycolytic route and occurred under con- 

 ditions in which ribonucleic acid synthesis was eliminated and deoxyribo- 

 nucleic acid synthesis stimulated. 



Also of interest are the recent investigations of Gibbs, Gunsalus, and 

 DeMoss on the fermentation of glucose by Leuconostoc mesenteroides^^-^^ 

 and Pseudomonas lindneri^^ to CO2 , ethanol, and lactic acid. Isotope data 

 have indicated the participation of an anaerobic hexose monophosphate 

 pathway in both organisms since, when glucose-1-C^^ was used, all the 

 radioactivity was recovered in the CO2 originating from Ci of the glucose 

 whereas if the fermentation had proceeded by the anaerobic glycolytic, 

 route, Ci of the glucose would have appeared in the ethanol. ^^ L. mesen- 

 teroides was shown to possess an active glucose-6-phosphate dehydrogenase 

 which is active with either DPN or TPN in contrast to the TPN-specificity 

 of this enzyme from other sources. 



The utilization of glucose-1-C'^ by growing yeast has been investigated 

 by Gilvarg,®^ but, since no evidence was found of preferential conversion 

 of Ci to CO2 , it was concluded that the direct oxidative pathway is not a 

 major route of carbohydrate degradation in growing yeast. 



3. As A Source of Pentose Phosphate for Nucleic Acid Synthesis 



The experiments of Cohen®" on the utilization of glucose by intact cells 

 of E. coll both during growth, when approximately three times as much 

 PNA as DNA is being synthesized,^" and during virus infection, when 

 DNA only is formed, were described in the previous section. Utilization of 

 Ci-labeled gluconate was also studied. Gluconate-adapted E. coli produces 

 a specific gluconokinase^^ catalyzing the phosphorylation of gluconate to 

 6-phosphogluconate, which then enters the direct oxidative pathway. 

 Since growth on gluconate was almost as good as on glucose, and 6-phos- 

 phogluconate cannot be converted enzymically to glucose-6-phosphate in 

 this organism, it appears that uninfected E. coli cells can produce sufficient 

 ribose and deoxyribose for their needs via the direct oxidative pathway. 

 During virus infection however, when the demand for deoxyribose is 

 greatly increased, gluconate is much inferior to glucose for virus and DNA 

 synthesis. Cohen concluded that ribose for PNA synthesis possibly origi- 

 nates in the direct oxidative pathway but that deoxyribose is generated 

 more readily from the anaerobic glycolytic route. 



" M. Gibbs and R. D. DeMoss, Federation Proc. 10, 189 (1951). 



6^ I. C. Gunsalus and M. Gibbs, J. Biol. Chem. 194, 871 (1952). 



«5 M. Gibbs and R. D. DeMoss, Arch. Biochem. and Biophys. 34, 478 (1951). 



66 D. E. Koshland and F. H. Westheimer, /. Am. Chem. Sac. 72, 3383 (1950). 



"C. Gilvarg, /. Biol. Chem. 199, 57 (1952). 



68 S. S. Cohen and D. B. M. Scott, Nature 166, 781 (1950), 



