KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



'We must, therefore, conclude that the question of the influence of 

 oxygen on the permeability of yeast cells has not yet definitely been 

 settled. 



'Nevertheless, it is difficult to conceive that anaerobiosis should 

 decrease the permeability of the yeast cells for the disaccharides under 

 consideration. For these cells show a normal Pasteur-effect with glu- 

 cose or well-fermentable disaccharides as fermentable substrates, prov- 

 ing that by withdrawal of oxygen the permeability for these sugars 

 either remains unchanged, or even - according to Dixon's conception 

 - is considerably increased. Now, it seems extremely improbable that 

 the cells behave quite differently towards supposedly unfermentable 

 disaccharides than towards the other sugars mentioned. 



'On rejecting the permeability hypothesis we have to accept the 

 second possibility, viz., that the inactivation is due to a reversible 

 change of the catalyst itself. Taking into account that withdrawal of 

 oxygen inevitably leads to an increase in the state of reduction in the 

 interior of the cell, it is only logical to assume that the said change is 

 connected with a reduction process. 



'Until now no evidence for the idea that carbohydrases are in- 

 activated by reducing agents is available' (p. 160). 



This statement is difficult to interpret. Does it mean that, by using 

 this negative phraseology, the authors tried to evade another problem 

 that could here be raised? For it is obvious that this explanation does 

 not answer the question why these same disaccharides can readily be 

 fermented by other yeasts under equally reducing conditions, so that 

 it could legitimately have been said that there was proof positive to 

 the effect that the hydrolases are not inactivated simply as a result 

 of the absence of oxygen. Moreover, Kluyver and Custers had ob- 

 tained from autolyzed yeast suspensions preparations exhibiting hydro- 

 lytic activity, and it should have been easy to test the effect of an- 

 aerobiosis and of reducing substances on the activity of the hydrolases. 

 Nevertheless, the publication contains no evidence that such experi- 

 ments were either carried out or even contemplated. These remarks 

 suggest that, once a reasonably satisfactory explanation had been 

 found, the problem was considered settled. It is, of course, possible 

 that the experiments had actually been made, but, contrary to expec- 

 tation, had yielded results that refuted the contention. A somewhat 

 similar situation has previously been discussed in connexion with 



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