BIOGRAPHICAL MEMORANDA 



cells, there is no clear reason why one should not go farther and 

 accept the supposition that in Pseudomonas putida there is only one 

 single oxido-reduction promoting agent which acts on all the sub- 

 strates . . . And the same conclusion holds good for all the primary 

 oxido-reductions which together constitute the typical fermentation 

 process of a cell. 



'This does not imply, however, that no specificity at all exists in 

 oxido-reduction promoting agents. On the contrary, we shall have to 

 seek, in the differences of the electrostatic properties of the agents of 

 different specific cells, the explanation why some of these cells dehy- 

 drogenate sugars only, others hydrocarbons as well, still others meth- 

 ylamine or nitrites. And we may cherish the hope that the time will 

 come when a wellfounded quantitative theory of catalysis will lead to 

 a sharp characterisation of the electrostatic properties of the different 

 catalysts, and in doing so make it possible to predict the nutritional 

 requirements of the corresponding cells' (p. 98-99). 



There is much in this reasoning that is as appealing as it is sound. 

 Ironically, the argument about a single dehydrogenating agent for a 

 large number of substrates has gained the strongest possible support 

 from the isolation of coenzymes I and II, their identification as di- 

 and triphosphopyridine nucleotides, and the finding that these are 

 the molecular species directly involved in the dehydrogenation of 

 numerous substrates. Admittedly, enzymological studies have also 

 established that these coenzymes function only in cooperation with 

 specific protein apoenzymes, so that the assumption of a multiplicity 

 of enzymes is still a necessary adjunct hypothesis. But this aspect has 

 gradually lost some of its perplexing consequences; the discoveries 

 pertaining to the apparently universal occurrence of common path- 

 ways, of a small number of cyclic mechanisms, and of the phenomenon 

 of induced enzyme synthesis have eliminated the need for assuming 

 that a particular cell is invariably equipped with as many types of 

 specific protein molecules as there are substrates it can utilize. 



In reading Kluyver's papers of this period during which he for- 

 mulated the general principles of metabolism, one may perhaps find 

 the approach too theoretical and speculative. This was also the crit- 

 icism of some of his contemporaries, one of whom complained that 

 what was really needed was 'more matter and less art'. Kluyver was 

 fully aware of this; but his philosophical inclination always made 



106 



