BIOSYNTHESIS OF PENTOSES 273 



additional reactions must also occur. Similar results were obtained with 

 pea root extracts.^^" 



Bloom and his co-workers"^ have attempted to evaluate the relative 

 importance of glycolytic and "oxidative" pathways using glucose-1-C^*, 

 glucose-U-C'^ (uniformly labeled glucose), lactate-1-C'*, lactate-2-C^'', and 

 lactate-3-C^^ as substrates. By relating the yields of C"02 from the labeled 

 lactates to those from the labeled glucoses, the maximal contribution of the 

 glycolytic pathway to the overall conversion of glucose to CO2 has been 

 calculated. No evidence of a nonglycolytic pathway was found either in the 

 intact rat or in diaphragm sections, whereas in kidney, and more strikingly 

 in liver slices, preferential conversion of Ci of glucose to CO2 indicated the 

 occurrence of an alternative pathway. In liver, this alternative pathway 

 accounted for at least 75 % of the CO2 formed from glucose. This somewhat 

 complicated experimental procedure has recently been modified and essen- 

 tially the same results have been obtained by comparing the yields of 

 C^^02 from glucose-6-C^'* and glucose-1-C^l"- The apparent discrepancy 

 between the results for the intact animal and for liver slices may be due to 

 a maskmg of the liver effect in the whole animal by muscle. The interpre- 

 tations of these results has been questioned by Katz et a?."^ Applying re- 

 vised equations to the same experimental data they calculated that with 

 rat liver slices, under the special conditions of Bloom et a/."' who incorpo- 

 rated acetate, lactate and gluconate into the medium, only 20 % of the CO2 

 is derived from glucose via the "oxidative" pathway. Without these addi- 

 tions less than 10% of the CO2 is formed by this route. Agranoff et a/.,"* 

 also using glucose-1-C^^ and glucose-6-C^^, have reported that with rat 

 liver slices there is a shift from the "oxidative" to the glycolytic pathway 

 in regenerating and embryonic liver and in butter yellow carcinomas. 

 Similar results were obtained after fasting and dinitrophenol treatment. 

 Additional work with C'^ labeled glucose has indicated the participation 

 of the "oxidative" pathway in the metabolism of Torula iitilis,^^^ Sac- 

 charomyces cerevisiae^^^ and various bacteria (see footnote 137). These 

 results with yeast conflict with those of Gilvarg^^ and Chance (see footnote 

 138). Bernstein"^ has continued his investigations on synthesis of ribose in 



3" M. Gibbs and B. L. Horecker, J. Biol. Chem. 208, 813 (19S1). 



" B. Bloom, M. R. Stetten and DeW. Stetten, Jr., J. Biol. Chem. 204, 681 (1953). 



3* B. Bloom and DeW. Stetten, Jr., J. Am. Chem. Soc. 75, 5446 (1953). 



« J. Katz, S. Abraham, R. Hill, and I. L. Chaikoff, J. Am. Chem. Soc. 76, 2277 (1954). 



" B. W. Agranoff, M. Colodzin, and R. O. Brady, Federation Proc. 13, 172 (1954). 



" J. C. Sowden, S. Frankel, B. H. Moore, and J. E. McClary, J. Biol. Chem. 206, 



547 (19S4). 

 " H. Beevers and M. Gibbs, Nature 173, 640 (1954). 

 " S. Weinhouse, Ann. Rev. Biochem. 23, 125 (1954). 

 '* E. Racker, Advances in Enzymol. 15, 141 (1954). 

 39 I. A. Bernstein, J. Biol. Chem. 205, 317, (1953). 



