76 



METABOLIC PATHWAYS IN MICROORGANISMS 



general outline, except for the use of specific inhibitors; 

 there are no good ones that have been discovered that have 

 an exclusive effect on the pentose cycle. 



We have carried out this detailed type of investigation in 

 a few situations; but I think you will agree that if one wishes 

 to survey a large number of new organisms, progress by this 

 means will be painfully slow. As opposed to this rigorous 

 method of investigation, we usually use a more "vigorous" 

 one, in which two general operations are employed: (a) 

 demonstration of the presence of the dehydrogenases for 

 G-6-P and 6-PGA; and (b) measurement of the non-oxida- 

 tive disappearance of ribose, followed by a search for the 

 transient formation of sedoheptulose and triose phosphates, 

 and the somewhat delayed accumulation of hexose phos- 

 phate. This type of behavior is noted in Fig. 3.7, which is 



I I 



I 



+ — + Ribose-5-phosphate 

 * • Hexose phosphate 



Sedoheptulose-7- phosphate 



Triose phosphate 



Fig. 3.7. Non-oxidative disappearance of added pentose from extracts 

 of pea aphid. Evidence for the pentose cycle in soluble extracts of the 

 pea aphid. 



