STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



177 



most often for the synthesis of the appropriate pentose phosphate derivable 

 from ghicose metaboHsm. 



2. " De Novo " Synthesis 



a. Pentose and Deoxypentose Synthesis. The rapid growth of knowledge in 

 this area began in 1948 with a resumption of study of the oxidative pathway 

 of phosphogluconate metabolism. The development of this subject through 

 1952 has been discussed by the author (Cohen, 1954). Pathways existing in 

 E. coli and indeed in most cells for the origin of ribose and deoxyribose can 

 be schematized as shown in formula (XXVI). 



ATP ATP 

 Glucose »'ClucQse-6-phosphQte'^ — ^Frvjctose-6-phosphQte >"Fructose-l, 6-diphosphate 



Dihydroxyacetone phosphate 

 i 



TPN 

 6-phosphogluconolactone 



i 



ATP 



Gluconate »-6-phosphogluconate. 



■CO2 



KPN 

 Ribulose-S-phosphate — Cj fragment Clyceraldehyde-3-phosphate 



1i 



Ri bose- 5- phosphate 



1i 



Ribose nucleotides . 



1i 



RNA 



II+CH3CHO 

 Deoxyribose-S-phosphate 



1 



-► Deoxyribotides 



i 



DNA 



Two alternative patlis of glucose utilization present in E. coli and in most other cells. 



(XXVI) 



It can be seen that each of the alternative paths stemming from glucose- 

 6-phosphate may produce the carbon atoms which form the sugars of the 

 nucleic acids. The determination of the quantitative relations of these 

 possible pathways in different organisms under different physiological condi- 

 tions has become a serious effort in many laboratories (Wood, 1955; AxeLrod, 

 1956a). The effect of virus infection on these pathways has been studied in 

 phage-infected E. coli (Cohen, 1954). 



The detailed enzymology of the pathways of pentose phosphate meta- 

 boUsm has been discussed m many recent reviews, e.g., AxeLrod (1956a), 

 which elaborate more recent information of the complex cycle involved. A 

 scheme of the reactions involving the pentose phosphates is presented in 

 formula (XXVII) (Horecker and Mehler, 1955). 



