54 



METABOLIC PATHWAYS IN MICROORGANISMS 



as the formation of triose phosphate or fructose-6-phosphate. 

 Now the disposition of these species is crucial: will the F-6-P 

 re-enter the pentose cycle as seems obligatory from the paper 

 by Katz and Wood, or will the triose be subjected in large 

 part to degradation via the Krebs cycle, as indicated for 

 this organism in the foregoing paragraphs? 



The radiorespirometric patterns in Fig. 2.9 and Table 

 2.2 provide the following information: (a) gluconate is 

 readily broken down, presumably after initial phosphoryla- 

 tion; (b) the route employed is not the Entner-Doudoroff 

 pathway, either alone or in combination with the pentose 

 cycle. In the Entner-Doudoroff pathway, there should be 

 metabolic equivalence between C-1 and C-4, C-2 and C-5, 

 or C-3 and C-6. This was not found. Instead, gluconate 

 appears to be metabolized via a sequence (Fig. 2.10): 



Glucose, 



G\ycoly 



Gluconate 



6-P 



Mg 



F-6>P 



i/f/ Glycolysis 



^ ^ Triose P 



i=F-l,6-P 



Glycolysis 



TCA Cycle 

 CO2, etc. 



Fig. 2.10. Simultaneous operation of glycol)sis and the pentose cycle, 

 and their effect on metabolism of administered glucose and gluconate. 

 Both circular loops represent pentose cycle operation: the outer loop 

 for the degradation of gluconate and a part of glucose; the inner, for 

 the portion of both glucose and gluconate metabolism that escapes 

 glycolysis after the first formation of triose phosphate, i.e., the portion 

 that recycles. 



