EVALUATION OF METABOLIC PATHWAYS 39 



caused by oxidation of regenerated endogenous metabolites, 

 and have attempted to account for the recycling of carbon 

 atoms that occurs in the pentose cycle; extensive calculations 

 are offered to show how this recycling would influence the 

 specific activities of respiratory CO2 from carbons 1, 2, 

 and 3 of glucose. However, although these workers assume 

 that glucose-6-P and fructose-6-P are in complete equilib- 

 rium, their treatment of data does not seem to allow ade- 

 quately for the possibility of diversion of hexose-P from 

 the pentose cycle into glycolysis. Their calculations appear, 

 in effect, to assume that carbon in the pentose cycle tends 

 to be recycled until it is oxidized to CO2. Moreover, no 

 drainage of the cycle intermediates is envisaged for other 

 cellular functions, and it is assumed that pentose cannot 

 be formed by reversal of the cycle, that is, by reversal of 

 the transaldolase-transketolase sequence. These points will 

 be dealt with in greater detail in the discussion on B. sub- 

 tilis oxidations, where the bulk of glucose catabolism is 

 routed via glycolysis, and also under the topic of the role 

 of the reductive pentose cycle in organisms. 



RADIORESPIROMETRY 



The third method has been called by us the radiorespiro- 

 metric method. You might expect that we would favor it, 

 since it was developed in our laboratories; but I believe 

 it to possess certain attractive features, and since we are 

 especially familiar with the method, I would like to explain 

 it to you. 



As developed by Dr. Wang and his colleagues, the radio- 

 respirometric method does not stress specific activities; it 

 measures instead the yields of 0^*02 from various metabo- 



