29 METABOLIC PATHWAYS IN MICROORGANISMS 



dition to the stoichiometry already quoted (23) which 

 demonstrates the preponderant use of the pentose cycle for 

 terminal oxidation of carbohydrate, there are several other 

 lines of evidence which indicate that acetate cannot be oxi- 

 dized by this organism. These are: 



1. Added acetate is not oxidized in simple manometric 

 experiments by intact cells or by cell-free extracts, either 

 alone or in the presence of glucose or glycerol as a potential 

 "sparker." 



2. When CHgCi^OOH is added to respiring cells, only 

 0.013% of the added C^* appears in the respiratory CO2, 

 even under conditions where 25% of the added C^* is 

 incorporated into the lipid fraction of the cells (see Table 

 1.8) (39). 



3. A. suboxydans extracts can form acetyl CoA in good 

 yield by the ATP-acetate-CoA reaction, yet the acetyl CoA 

 formed cannot be converted to citrate or acetyl sulfanila- 

 mide. The organism evidently lacks a suitable acceptor 

 system; only when the acceptor fraction from pigeon liver 

 [Chou and Lipmann (40)] is added can acetyl sulfanilamide 

 be produced, and only when pigeon liver condensing en- 

 zyme is added can citrate be formed. 



4. Pyruvate does not form acetyl CoA during oxidation 

 unless ATP is added (39). This suggests that free acetate 

 is produced before acetyl CoA is formed. 



The Citric Acid Cycle, The statements in the four pre- 

 ceding paragraphs imply that the Krebs citric acid cycle may 

 not function in A, suboxydans. This is of course surprising, 

 for other species of Acetobacter such as A. pasteurianiim 

 (41) and A. aceti (42) have been shown to possess a full 

 complement of Krebs cycle enzymes, as indeed virtually all 



