22 METABOLIC PATHWAYS IN MICROORGANISMS 



organisms do. Moreover, the idea that such a universally 

 important complex of metabolic machinery should be com- 

 pletely absent from any aerobic organism that can oxidize 

 glucose to CO2 and H2O, is not likely to gain full accept- 

 ance—even by those who work with the organism— without 

 careful checking. We have scrutinized this problem care- 

 fully, but all data point to the absence of a traditional citric 

 acid cycle in A. suboxydans [to the extent that these reac- 

 tions have been studied, they have in general been verified 

 by Rao (42)]. The pertinent data are: 



1. Failure to form citrate from acetyl CoA, as outlined in 

 part 4 of the previous section. 



2. Failure of either whole cells or cell-free extracts of A. 

 suboxydans to oxidize, succinate, fumarate, malate, or a- 

 ketoglutarate. Oxalacetate is oxidized to pyruvate and ace- 

 tate. The only other citric acid cycle member to be oxidized 

 at all is citrate, and this only slightly. The possible signifi- 

 cance of this oxidation is being examined further. 



3. The quantitative data on C^^02 arising from cells 

 oxidizing glucose- or gluconate- 1-, 2-, 3,4-, 6-, or U-C^-^ 

 indicate that the pentose cycle is the terminal oxidation 

 route in this organism. There is no indication that glycoly- 

 sis or the Krebs cycle are operative (23). 



Glycolysis, A. suboxydans displays high aldolase and tri- 

 ose phosphate isomerase activity, and might be supposed 

 to carry out glycolysis in the usual manner. However, the 

 failure to produce significant amounts of acetate from 

 glucose (lactate and pyruvate are quantitatively converted 

 to acetate) has cast doubt upon the presence of a typical 

 Embden-Meyerhof dissimilation scheme. The presence of 

 individual enzymes characteristic of glycolysis does not of 

 itself assure glycolytic action, since every enzyme in the 



