DISCUSSION ON BACTERIAL RESPIRATION 263 



teria. These bacteria either oxidize glucose directly without previous 

 phosphorylation {Pseudomonas aeruginosa) or oxidize directly phos- 

 phorylated hexose (hexose monophosphate and diphosphate). 



The same variety of mechanisms is found in the oxidation of pyru- 

 vate (CH3COCOOH + 'AO^ = CH3COOH + CO2): it requires an 

 iron porphyrin catalyst in gonococci; it proceeds without iron por- 

 phyrin in Bacterium Delbriickii, as Lipmann has shown. d-Amino 

 acid oxidase, isolated by Warburg and Christian, is an alloxazin 

 dinucleotide protein, the oxidation of alanine to pyruvate being 

 cyanide-insensitive; this oxidation when performed by cytochrome- 

 containing bacteria requires iron porphyrin as a component of the 

 enzyme system because the oxidation is completely inhibited by 

 cyanide. 



These examples are presented as proof of the existence of multiple 

 mechanisms of oxidation. A comprehensive study of biologic oxida- 

 tion-reduction demands, therefore, a continuous and simultaneous 

 attention to the oxidation mechanisms throughout living cells. 



P. W. Wilson, University of Wisconsin: 



A discussion of oxidations by aerobic bacteria should certainly 

 include reference to the fact that one of the most actively respiring 

 tissues known belongs to this group of organisms. I refer, of course, 

 to the extremely high rate of respiration possessed by certain cultures 

 of Azotobacter, the free-living nitrogen-fixing bacteria. One of our 

 distinguished guests and participants. Dr. Otto Meyerhof, first called 

 attention to this several years ago when he reported Q02 values of 

 500 to 8600 for Azotobacter chroococcum on glucose at 28° C. (1, 2). 

 The extremely high values were obtained with very young cultures 

 so diluted that the total dry weight involved was less than 10 micro- 

 grams. Its estimation may have been subject to some error, but it is 

 probable that young cultures of this organism have a Q02 value of 

 at least 5000. 



Since Meyerhof and his collaborators made these experiments, 

 important advances have been made toward developing cultural 

 conditions that are optimum for growth and nitrogen fixation by 

 Azotobacter. Bates of fixation are consistently obtained in experi- 

 ments today which are several times greater than those reported 

 several years ago. For example, Azotobacter vinelandii can fix as 

 much as 20-30 mg. of nitrogen in 24r-36 hours instead of 4-5 mg. in 

 one or two weeks which was the characteristic result of most of the 



