12 METABOLIC PATHWAYS IN MICROORGANISMS 



free passage of glucose or its phosphate from one oxidizing 

 system to another, yet this imphes that no "pool" of glu- 

 cose derivatives exists. While this has neither been proved 

 nor disproved, it seems not to be a tempting conclusion. 

 In the organism B. suhtilis, kinetic experiments with iso- 

 topically labeled gluconate suggest strongly that a "pool" 

 of glucose exists, and that gluconate when reconverted to 

 hexose via the pentose cycle is labeled in accordance with 

 expected patterns, as will be seen in the next chapter. Spa- 

 tial separation might seem to provide a plausible explana- 

 tion for the plethora of separate enzymes that exists for 

 oxidation of individual, or closely related, substrates. 



Dihydroxyacetone Phosphate, Dihydroxyacetone phos- 

 phate was converted, after its formation from glycerol, to 

 fructose 1, 6-diphosphate through the action of the iso- 

 merase-aldolase system, which was found to be very active 

 in this organism (19). With dihydroxyacetone as the start- 

 ing material, it was possible, in the presence of ATP and 

 Mg- + , to show the formation of fructose in amounts (as 

 measured by the resorcinol test) approaching theory based 

 on the ATP present, assuming activity of ADP. The re- 

 actions could also be followed through measurement of the 

 inorganic phosphate released. Under oxidative conditions 

 (DPN and triphenyltetrazolium) a further, slower release of 

 P^ was observed, as would be expected if the pentose cycle 

 were operating, and hexose accumulation dropped to about 

 one-tenth of the amount formed non-oxidatively. In the 

 presence of Mg- + , a material was formed that produced two 

 paper chromatogram spots characteristic of an authentic 

 mixture of glucose-6-P and fructose-6-P. The scheme is 

 shown in Fig. 1.3, together with subsequent reactions of the 

 pentose cycle. 



When the oxidation of glucose-6-phosphate was followed 



