BIOGRAPHICAL MEMORANDA 



Under anaerobic conditions all of these organisms, in suspensions 

 containing a fermentable sugar, caused the establishment of a redox 

 potential of 80-100 mV. The concordant data therefore suggested 

 that this is the potential characteristic for alcoholic fermentation. To- 

 gether with the marked difference in the potentials of cultures of 

 denitrifying bacteria, this further strengthened the belief that the 

 redox potential may serve to define a specific type of metabolism, a 

 first and important step in the direction of a quantitative description 

 of metabolic processes in electrochemical terms. But it soon appeared 

 that in the case of alcoholic fermentation the measured potentials 

 conflicted with observations made by the use of other techniques, for 

 shortly afterwards Fromageot and Desnuelle [1935] showed that a fer- 

 menting yeast suspension can reduce dyes, such as Nile blue, whose nor- 

 mal potential is considerably lower than the potentials determined by 

 Kluyver and Hoogerheide. This, of course, implied that the reducing 

 capacity of such a suspension must be much greater than what could 

 be surmised from the values established with the aid of noble metal 

 electrodes. 



Once again theoretical considerations of the situation provided a 

 solution of this problem. In a subsequent publication Kluyver and 

 Hoogerheide [1936b] argued that the potentials they had determined 

 must be ascribed to the presence around the electrodes of a redox 

 system of unknown composition that had diffused out of the metab- 

 olizing cells into the surrounding medium. At first the nature of this 

 system, referred to as the 'bio-indicator', had been deemed unim- 

 portant. But now it became clear that this was not necessarily so; 

 after all, the electrode can only measure a potential that is deter- 

 mined by the continuous interaction of the bio-indicator system with 

 the electrode on the one hand, and with the intracellular catalysts on 

 the other. The argument continues: 



'Now in the previous communications we had tacitly assumed that 

 the bio-indicators secreted by the cells would be able to display their 

 mediating function over the entire range of potentials concerned in 

 the metabolic activity. On closer consideration this may, however, be 

 doubted. ... It is by no means evident why it should be a general pro- 

 perty of living cells to excrete into the surrounding medium an unin- 

 terrupted series of redox systems with decreasing normal potentials. Thus 

 it is possible, nay, even probable that the oxido-reduction processes 



