H. GAFFRON 



of obscure metabolic reactions. Among younger biochemists the 

 attitude toward a field like photosynthesis is one of waiting until dis- 

 agreeable obstacles have been cleared away by hand, so to speak, so 

 that they may roll in with modern methods. During the past twenty 

 years the moment when this will happen has quietly drawn nearer. 

 How near we shall try to demonstrate in the rest of this essay. 



It is mostly forgotten that, after Buchner had demonstrated 

 fermentation outside the living cell, some thirty years passed before 

 enzymes were isolated and the mechanism of organic catalysis could 

 be said to be clearly understood. Progress in the field of cellular break- 

 down reactions, slow in the beginning of this century, nevertheless 

 encouraged a handful of students to devote their lives to the investiga- 

 tion of respiration and fermentation. In contrast, the return for the 

 toil directed toward solving the problem of photosynthesis was so small 

 that even the leading biochemists, after establishing a few important 

 new facts such as the existence of a photochemical reaction distinguish- 

 able from an enzymic one, saw no point in pursuing the analysis any 

 further. In 1918, Willstatter wrote that it was evidently too early 

 to try to elucidate the mechanism of carbon dioxide assimilation in 

 living cells. We now know that he was right. At that time photo- 

 synthesis appeared as an absolutely unique process showing no con- 

 nection or analogy with other metabolic processes in the cell. It was 

 looked upon as a direct photochemical decomposition of carbon dioxide 

 and mysteriously connected with the phenomenon of life on earth. 



The absolute ignorance of the kind of reactions photosynthesis 

 might involve and, consequently, the lack of a theoretical framework 

 accurate enough to direct a reasonable approach barred further 

 progress. And as to purely empirical experimental attempts, they 

 all ended with the destruction of the intact living cell. Photosynthesis 

 stops the moment the cell is hurt. While this is still true, of course, 

 the great diflference is that today we know more or less why. Hence 

 there is hope we shall be able to overcome this difficulty. 



Despite Miller's verdict quoted above, there has been very 

 decisive progress between 1918 and 1938, not merely by the addition 

 of several important observations to a hundred earlier ones but, mainly, 

 by the change in our conception of what constitutes the problem of 

 photosynthesis. This change was due, on the one hand, to the under- 

 standing of the nature of other metabolic processes such as respiration 



32 



