26 METABOLIC PATHWAYS IN MICROORGANISMS 



rapidly. However, its specific activity does not reach that 

 of orthophosphate, but levels off at about half that value. 



4. After prolonged incubation, the specific activities of 

 the labile groups in ATP and ADP approach that of inor- 

 ganic p))?"ophosphate, not orthophosphate. 



5. About five to ten times as much high polymer meta- 

 phosphate is found as is ATP. This material is slowly 

 labeled by added P^-04^~, although there is some evidence 

 that metaphosphate may be formed in resting cells oxidiz- 

 ing fructose and glycerol. 



These data point strongly to inorganic pyrophosphate as 

 an intermediate in oxidative phosphorylation, in A. siib- 

 oxydans as well as in yeast. The origin of pyrophosphate 

 remains to be studied; it may arise through interaction of 

 polymetaphosphate with P^-0/~. 



SUMMARY 



The organism A. suhoxydans thus presents a variety of 

 behaviors that makes it seem curious indeed. Its special 

 behavior toward glucose has made it possible to recognize a 

 number of reactions, which, although present in other 

 organisms as well, are easier to view here because of the 

 absence of a functioning Krebs cycle. The Krebs cycle, 

 if present, might serve to remove many of the metabolites 

 that are now recognizable. The documentation of the 

 pentose cycle, both with respect to its extent and its abun- 

 dance, will be treated in the next chapter, where attention 

 is paid to the complex problem of evaluating pathway par- 

 ticipation in whole cells through the use of isotopes. 



