KLUYVER S CONTRIBUTION'S TO MICROBIOLOGY AND BIOCHEMISTRY 



carboxylic acid cycle, had been clarified that a rational interpretation 

 could be advanced. 



Meanwhile Kluyver's theory of metabolism had also opened the 

 way to a re-interpretation of the mechanism of photosynthesis. In 

 'Die Einheit in der Biochemie' this was foreshadowed in the brief 

 discussion of the properties of the purple sulphur bacteria. Here it was 

 pointed out that the earlier attempts of Winogradsky, Engelmann, 

 Molisch, and others to account for the behaviour of these organisms 

 suffered from the fact that they had attributed the importance of light 

 for the development of the purple bacteria to the production of oxygen 

 by a decomposition of carbonic acid with the aid of absorbed radiant 

 energy, even though 'no one has yet succeeded in demonstrating 

 oxygen production under the most diverse conditions'. But once the 

 dehydrogenation theory of biochemical reactions is accepted, this 

 fundamental difficulty disappears because 'it is then no longer im- 

 perative to assume that the acceptor for the dehydrogenation of hy- 

 drogen sulphide or sulphur must needs be oxygen ; it would be entire- 

 ly possible for some other acceptor to play this role. It is merely nec- 

 essary to retain the principle that the hydrogenated acceptor com- 

 pound can transfer the hydrogen to carbon dioxide with the aid of 

 radiant energy' (p. 175). 



The work begun in Kluyver's laboratory on the metabolism of the 

 purple bacteria soon led to a generalized formulation* of photosyn- 

 thesis as a light-dependent transfer of hydrogen to carbon dioxide with 

 a concomitant dehydrogenation of an appropriate oxidizable sub- 

 stance, H 2 A, according to the overall equation: 



light 

 C0 2 +2H 2 A -> CH 2 0+H 2 0+2A, 



an exact counterpart of Kluyver's equation expressing the metabolic 

 processes of non-photosynthetic organisms. This formulation made it 

 clear that oxygen evolution in photosynthesis will be observable only 

 if H 2 is the ultimate hydrogen donor for the reduction of carbon 

 dioxide; in all other cases a different dehydrogenation product, 'A', 

 should make its appearance. Afterwards Muller [1933Tb], on the 

 basis of experiments concluded in Kluyver's laboratory, established 

 that organic substances may serve as hydrogen donors in purple bac- 



* Ed. note: C. B. van Niel. Arch. Mikrobiol. 3, 1, 1931. 



