THE ACETIC ACID BACTERIA 25 



a transient existence, due to the presence of a very active 

 glyoxylate reductase (glycolic dehydrogenase) in the organ- 

 ism (49). This enzyme, studied in detail in plants by Zelitch 

 (50), has an equilibrium constant of 1 X 10~^'^ in the 

 direction glycolate -^ glyoxylate; hence only traces of gly- 

 oxylate could be present at any moment. 



PHOSPHORYLATION 



The non-phosphorylative oxidations of this organism 

 presumably proceed without capture of the released energy, 

 at least as nucleotide polyphosphates. These oxidations 

 are not inhibited by dinitrophenol (51). In contrast, the 

 oxidations beyond the first step, i.e., those in the pentose 

 cycle, are phosphate dependent and, as mentioned earlier, 

 are dinitrophenol sensitive. 



This observation prompted a more complete investigation 

 of oxidative phosphorylation in A. suhoxydans. Using 

 glucose, glycerol, and fructose as substrates and P^-04^^ 

 as a tracer, it was found (52) that oxidative phosphorylation 

 in this organism differs in certain important respects from 

 the corresponding process in animal tissues. Thus, 



1. Unlike animal systems, but like many other microbial 

 systems, the P/O ratios are low, averaging about 0.5. 



2. The nucleotides that are active in phosphorylation 

 are present in low concentrations (about 1.5 /^moles ATP 

 per gram of respiring cells). It has not been possible to 

 increase these values through the addition of acceptors. 



3. Inorganic pyrophosphate is present in relatively large 

 amounts (about one-eighth that of ATP) and turns over 



