44 METABOLIC PATHWAYS IN MICROORGANISMS 



activity would show equal yields of CO2 from carbons 1 and 

 4 of glucose. 



Gp — 



Gi — G4 



Gt 



Ged (Entner-Doudoroff) is taken as the remainder 



The types of CO2 production curves obtained vary from 

 organism to organism; four of these are reproduced here 

 to show the characteristic differences that exist. 



1. In bakers' yeast, Fig. 2.SA shows that the greatest evo- 

 lution of CO2 is from carbons 3 and 4, characteristic of 

 glycolysis. (The general availability of this species of glu- 

 cose dictates its routine use over glucose-S-C^*; it is as- 

 sumed here that the yield in CO2 is equal from both car- 

 bon atoms.) C^^02 production from C-1, although higher 

 at first than from C-6, is much lower than from C-3,4- The 

 curve for interval recovery of CO2 from C-3,4 reaches a 

 maximum at about 2 hours, then drops to a minimum at 

 4 hours; the latter time coincides with complete removal 

 of the administered glucose from the medium. This time 

 is defined as I relative time unit (1 RTU) and is used to 

 make comparisons more relative among different organisms 

 (Streptomyces griseus, for example, exhibited a much slower 

 metabolism under the experimental conditions used than 

 did bakers' yeast; 1 RTU was about 10 hours). After 1 

 RTU the accumulated radioactivity in the cells and medium 

 undergoes depletion; yields of Ci^02 from carbons 2 and 6 

 increase in that order, as would be expected from oxidation 

 of acetate via the TCA cycle. 



2. The second type is exemplified by Zymomonas mo- 

 bilis; the C^^02 yields agree with the contention that the 



