EVALUATION OF METABOLIC PATHWAYS 43 



calculation of the fraction of the total metabolism that 

 travels by the pentose pathway (with and without recycling) 

 is measured as 



Gp — 



Gi — Gq 



Gt 



where Gp = fraction of glucose participating in phospho- 

 gluconate decarboxylation 

 Gi\ Gq^ = total activity in respiratory CO2 from cells uti- 

 lizing equal amounts of C-1 or C-6 labeled 

 glucose 

 Gt = total activity of the administered substrate (al- 

 ways taken as 100%, or unity) 



The fraction of glucose catabolized by glycolysis, G^ (Emb- 

 den-Meyerhof-Parnas pathway) is 



Ge = 1 — Gp 



This assumes that the Entner-Doudoroff pathway does not 

 simultaneously operate. In our experience W'ith various 

 organisms, this assumption seems generally safe. When the 

 Entner-Doudoroff pathway is present, glycolysis is seen gen- 

 erally to have subsided, and the recognition of Entner-Dou- 

 doroff activity (separately from the pentose cycle) is made 

 by noting the difference between the yield of CO2 from car- 

 bons 1 and 4 of glucose, since exclusive Entner-Doudoroff 



of incubation flask; c and p, aeration tubing (glass) with lower end 

 protruding into incubation flask; d, rubber tubing; e, air inlet; /, flow- 

 meter; g, three-way stopcock; h, CO2 trap; i, needle valve, to regulate 

 gas flow; /, tension clamp for release of trap solution; k, clamp for 

 holding trap solution receiver; n, trap solution receiver. (Courtesy of 

 Krishell Laboratories, Portland, Oregon.) 



