KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



the fermentative and oxidative metabolism of yeast in which it had 

 been shown that fermentation can be completely suppressed by con- 

 centrations of the poison that had no appreciable effect on the oxi- 

 dative metabolism. 



Kluyver and Hoogerheide [1933b], after having corroborated Lunds- 

 gaard's experiments and determined the exact concentration of iodo- 

 acetic acid that produced the differential effect under the conditions 

 of their experiments, then found that even the slightest raise in con- 

 centration of the inhibitor immediately affected the respiratory activ- 

 ity as well. This result was used to defend the thesis that the situation 

 was fully compatible with the unitary theory. The argument was 

 developed on the basis of the following assumptions : 

 /. Methyl glyoxal is the immediate substrate for both fermentation 

 and oxidation; 2. oxidation takes precedence over fermentation, but 

 the rate of the former is limited by the capacity of the oxygen-activ- 

 ating catalyst; 3. in the absence of iodoacetic acid the rate of methyl 

 glyoxal formation greatly exceeds that of oxygen activation, so that 

 under these conditions a considerable surplus fermentation will be 

 observable; and 4. the principal effect of iodoacetic acid is that it 

 diminishes the rate of formation of methyl glyoxal. 



From these assumptions it logically followed that an inhibition of 

 the oxidative sugar metabolism of yeast by iodoacetic acid can be 

 expected only if its concentration has become sufficiently high to 

 cause the rate of methyl glyoxal formation to drop to the point where 

 it is less than the rate of oxygen activation; at lower concentrations 

 the poison will merely cause a decrease in the rate of fermentation. 



This explanation is certainly not without merit. But the above as- 

 sumptions also imply that, at the concentration where iodoacetic 

 acid just begins to inhibit the respiratory metabolism, methyl glyoxal 

 must still be generated at a commensurate rate, so that at this concen- 

 tration a comparable rate of fermentation should still be observable 

 under anaerobic conditions. This is contrary to fact. Kluyver and 

 Hoogerheide were well aware of this difficulty, and explained the 

 disturbing fact by invoking the auxiliary hypothesis that, in addition 

 to inactivating the methyl glyoxal-producing enzyme system, iodo- 

 acetic acid also causes an oxidation of reduced glutathione which latter 

 substance would play a vital role in the fermentation reactions proper. 



Similarly, the early studies by Kluyver and co-workers on the oxi- 



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