BIOSYNTHESIS OF PENTOSES 249 



Glucose-6-phosphate 



TPN K'02 

 6-Phosphogluconate 



TPN 



HO2 



2-Keto-6-phosphogluconate 

 — CO2 

 Ribose-5-phosphate 



TPN 



MO2 



5-Phosphopentonate 



Tetrose-4-phosphate, etc. 

 Fig. 1. Dickens' scheme for oxidation of glucose-6-phosphate bj^ j'east enzymes. 



spect. It was suggested that during the oxidation of 6-phosphogluconate the 

 necessary change of configuration occurred at carbon atom 2 of the pentose 

 to give D-ribose-5-phosphate. Isolation of the oxidation products of 6- 

 phosphogluconate was attempted by both Dickens^ and Warburg and 

 Christian^ and evidence obtained of the formation by successive oxidations 

 and decarboxylations of 65,04, and C3 phosphates, but none of these was 

 identified. One of the Cs compounds^ gave a strong pentose color reaction. 

 Dickens' scheme for the sequence of events in this pathway is given in 

 Fig. 1. 



2. Recent Work on the Identification of Pentose Phosphates 



a. Ribose-5 -phosphate 



The possible physiological significance of this oxidative pathway was 

 apparently not appreciated by the early workers in this field since no 

 further systematic work was done for over ten years when Scott and Cohen 

 reinvestigated Dickens' yeast system. Their primary interest was in the 

 origin of ribose and deoxyribose for incorporation into nucleic acids and in 

 the nature of the diverted metabolism in virus-infected bacteria. ^° Using 

 a crude yeast enzyme preparation," the products of enzymic degradation 

 of 6-phosphogluconate were isolated, fractionated, and analyzed,^^ pentose 



9 O. Warburg and W. Christian, Biochem. Z. 292, 287 (1937). 

 " S. S. Cohen, Cold Spring Harbor Symposia Quant. Biol. 12, 35 (1947) ; J. Biol. Chem. 



174, 281 il9i8); Bacterial. Revs. 13, 1 (1949); 15, 131 (1951). 

 11 F. Dickens and H. Mcllwain, Biochem. J. 32, 1615 (1938). 



" D. B. M. Scott and S. S. Cohen, Science HI, 543 (1950); J. Biol. Chem. 188, 509 

 (1951); J. Celhdar Comp. Physiol. 38, Suppl. 1, 173 (1951). 



