34 METABOLIC PATHWAYS IN MICROORGANISMS 



C 1 COOH 



I I 



C 2 C^O Pyruvate 



I I 



C ^ 3 CH3 



+ < + 



C "^4 CHO 



I I 



C 5 CHOH Glyceraldehyde-3 -phosphate 



C 6 CH2OPO3H2 



2-Keto-3-deoxy- 

 6 - phosphogluconate 



Fig. 2.4. The fate of the carbon skeleton of ghicose in the Entner- 

 Dotidoroff pathway. 



group. The specific activity of the respiratory C^^Oo should 

 be identical whether glucose- l-C^^ or glucose-6-Ci^ is ad- 

 ministered to the test system. 



If, on the other hand, phosphogluconate decarboxylation 

 prevails, carbon 1 of glucose will be quickly converted 

 to respiratory COo. If this carbon is labeled, the CO2 will 

 be substantially enriched with C^^, whereas if carbon 6 

 is labeled instead, the CO2 will have little or no activity 

 at first, and will become more active only as the pentose 

 cycle operates to relocate active carbon atoms into the oxi- 

 dizable position of the glucose molecule. Figure 2.2 indi- 

 cates the fate of individual carbon atoms as they traverse 

 the cycle; this scheme has been reported by Beevers (1) 

 for plant systems, and work in Dr. Wang's laboratory with 

 B. siibtilis oxidations indicates that the scheme outlined 

 may operate in this fashion in this organism as well.^ 



1 Beevers' scheme is sHghtly different from the one presented by Kitos 

 et al. (4); see Fig. 2.3. The latter, which showed one molecule of hexose 



