PASTEUR EFFECT 55 



Although a broader discussion of the theory of the Pasteur effect 

 is reserved for a later paragraph, some interesting experiments re- 

 lating to the constancy of the Meyerhof Quotient may be mentioned 

 here. These experiments on the effect on the oxidation quotient of 

 the Z-factor of v. Euler, a factor stimulating only fermentation, are 

 taken from a paper by Meyerhof and Iwasaki (11). See Table 3. 



For the same yeast, Q values, the oxidation quotient, and the 

 percentage of inhibition are hsted with and without the stimulating 



Table 3.— Influence of medium on fermentation and oxidation 



quotient 

 (Reference 11) 



* Meyerhof oxidation quotient. 



factor. Here with the same respiration but variations in anaerobic 

 and aerobic fermentation, the relative influence of respiration on 

 the disappearance of fermentation increases, whereas the per- 

 centage of inhibition remains constant. These experiments are more 

 consistent with an explanation of the Pasteur effect as an inhibition 

 of some kind resulting from the presence of oxygen but independent 

 of the magnitude of respiration. Similar results were recently re- 

 ported by Burk, Winzler, and du Vigneaud (12), who studied tlie 

 metabolism of a biotin-deficient yeast. They found oxidation quo- 

 tients up to 20, whereas 12 is the theoretical maximum for a re- 

 synthesis theory. 



The results of these experiments are discussed in some detail in 

 order to draw attention to two lines of approach to an explanation 

 of the phenomenon. The first set of data, showing parallel rates of 

 respiration and fermentation disappearance suggests an interaction 

 between the two lines of reaction which leads to the establishment 

 of a dynamic equilibrium of some kind. The second set of data 

 shows conditions where the aerobic inhibition of increased fermenta- 

 tion is independent of the rate of respiration, which remains prac- 

 tically constant. This suggests a direct inhibition through oxygen. 



