THE PHOSPHOGLUCONATE OXIDATION PATHWAY 219 



pathway. One group of methods is based upon the fact that operation 

 of the phosphogluconate oxidation pathway results in a preferential 

 liberation of the aldehyde carbon of glucose as carbon dioxide. The 

 limitation of this approach is that glucose goes through many more 

 metabolic pools and is more diluted in the Embden-Meyerhof than in 

 the oxidative pathway before liberation of carbon dioxide; this results 

 in a bias which may exaggerate the contribution of the oxidative path- 

 way. Application of various modifications of this method indicates 

 that there is a substantial flow of carbon over some pathway prefer- 

 entially liberating carbon- 1 of glucose as carbon dioxide in Penicillium 

 chrysogenum (80, 124), Aspergillus oryzae (6), Streptomyces coelicolor 

 (66), and Neurospora crassa (293). A modification of this method 

 indicates that in growing mycelium of Penicillium chrysogenum 

 about 60 per cent of the glucose carbon goes over the oxidative path- 

 way (124), while in Fusarium lini a minimum of 17 per cent of the 

 glucose catabolic mechanism involves preferential liberation of car- 

 bon-1 (125). 



A more promising method involves determination of acetate, 

 ethanol, pyruvate, or compounds derived therefrom during aerobic 

 respiration of specifically labeled glucose (26, 318). Application of 

 this technique to Penicillium chrysogenum suggests that the Embden- 

 Meyerhof pathway is the principal route of glucose breakdown (172). 

 Still other methods may be applicable but have not yet been tested in 

 the fungi (18, 19, 23, 24, 105, 139, 156, 236, 268). Wood (327) discusses 

 the methods critically and points out their limitations. 



In Aspergillus niger the distribution of isotope in citric acid in- 

 dicates that the Embden-Meyerhof sequence accounts for 80 per cent 

 of the total aerobic glucose catabolism (261). Similarly, in Ustilago 

 zeae the labeling of the carbohydrate moiety of the glucolipid ustilagic 

 acid is consistent with the resynthesis of glucose from triose phosphate 

 and consequently with the operation of the Embden-Meyerhof path- 

 way (29). The labeling of kojic acid formed by Aspergillus flavus 

 from pentose is, on the other hand, suggestive of a preliminary con- 

 version of pentose, through the non-oxidative phase of the phospho- 

 gluconate pathway, to hexose (8). 



The various approaches which attempt to utilize labeled sugars each 

 has its own difficulties and ambiguities, and we should regard the data 

 collected so far as preliminary and tentative. Some attempt should be 

 made to see whether two different methods agree with regard to the 

 same material before reliance can be placed on any single method. 

 There seems little doubt that the phosphogluconate oxidation pathway 

 is utilized by many fungi and actinomycetes, and it is not unreasonable 



