EVALUATION OF METABOLIC PATHWAYS 47 



Fig. 2.8. Time-course plots of radiochemical recoveries in CO2 from 

 metabolizing specifically labeled glucose. 



(A) Bakers' yeast: 1 RTU = 4 hours. 



(B) Zymomonas mohilis (formerly called Pseudomonas lindneri): 

 1 RTU = 4 hours. 



(C) A. suboxydans: 1 RTU = 4 hours. 



(D) B. subtilis: 1 RTU = 4.5 hours. 



In all systems, the following legends are employed: ., 



glucose-l-Ci4; -, glucose-2-Ci4; , glucose-3,4-Ci4; 



, glucose-4-Ci4; and — • — , glucose-6-Ci4. Inserts: cumu- 

 lative recoveries of Ci40o. 



Since oxidation of C-6, -5, or -4 required recycling, we can 

 assume that the maximal yield of C-4 in COo will be ap- 

 proximately 88% of C-6, = (33/100) X 0.88 = 29%. Also, 

 since C-3, 4 "average" recovery = 46%, recovery of C-3 -f 

 C-4 = 92%. Therefore, minimal recovery of C-3 = (92 — 

 29)/100 = 63%. 



This calculated value for recovery of C-3 in the respira- 

 tory COo agrees well with the observed value for C-2 re- 

 covery from glucose (63%; Table 2.1) and thus confirms 

 the pentose cycle as the only significant pathway for com- 

 plete oxidation of glucose in the organism concerned under 

 the conditions which prevailed. 



This calculation, although different from that of Katz 

 and Wood (9) nevertheless takes into account much of the 

 complexity of recycling of F-6-P. In an organism that relies 

 on the pentose cycle as extensively for oxidation of glucose, 

 one would expect that in resting cells the combustion of 

 glucose carbon atoms 2 through 6 should approach equal 

 magnitude with carbon 1, although they may do so more 

 slowly. The fact that they do not, even at the end of the 



