KLUYVER S CONTRIBUTIONS TO MICROBIOLOGY AND BIOCHEMISTRY 



tures of these organisms, and Roelofsen [1934], in the course of his 

 investigations of the metabolism of the purple sulphur bacteria, meas- 

 ured the potentials in suspensions of a Chromatium species, both in 

 darkness and when exposed to light, thereby revealing that illumina- 

 tion caused an instantaneous shift of the potentials to a new level, 

 some 100 mV more positive than that of the suspension in darkness. 

 While these measurements were of a rather incidental nature, this 

 cannot be said of the study of Cozic [1936], who determined the poten- 

 tials of suspensions of acetic acid bacteria during the oxidation of 

 alcohol. This investigation was conducted with six different Acetobacter 

 species, including A. peroxydans and A. suboxydans, thus covering the 

 entire range of representatives with different oxidative capacities. It 

 was found that, regardless of the species used, the potential was the 

 same in all cases. This, no doubt, must have made Kluyver realize 

 that the measured potentials were determined exclusively by the par- 

 ticular metabolic process taking place in the suspensions of the mi- 

 crobes under investigation; and it is probable that this recognition 

 eventually convinced him that redox potentials could not provide the 

 requisite data to define the 'affinity for hydrogen' of different organ- 

 isms, which had been the primary aim of these studies and was in- 

 tended to serve as the basis for a quantitative theory of biocatalysis. 

 This would account for the fact that after 1936 no further work on 

 this subject appears to have been carried out in his laboratory. 



That the decision to abandon this project was a sound one has 

 become clear from the results of a quarter century's research on iso- 

 lated enzyme systems. For, although current knowledge of the redox 

 potentials of these entities has made it possible to assign to many of 

 them a definite place in the sequence in which they participate in 

 biochemical reactions, it is apparent that 'affinity for hydrogen' is 

 certainly not the only factor that determines their activity. However 

 much enzyme research may have contributed to our understanding 

 of the detailed mechanism of biocatalysis, it has not yet led to the 

 emergence of concepts that can explain the potentialities of various 

 microbes to metabolize diverse types of substrates without invoking a 

 considerable degree of arbitrariness in the distribution of specific en- 

 zymes among the organisms. Whether this will ever be feasible can 

 only be decided by future developments. 



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