H. GAFFRON 



boxyl group seems to be attached, Franck considers the influence 

 which the presence of carbon dioxide exerts on the intensity of chloro- 

 phyll fluorescence in vivo as the most cogent evidence supporting this 

 view. The scheme shown on page 35 does not do justice to these 

 important considerations. 



In case, however, the fluorescence experiments could be ex- 

 plained in another way, there would be no objection against assuming 

 the existence of an intermediate hydrogen donor. Perhaps catalyst B 

 of Franck and Herzfeld might play this part (4). Its concentration 

 should be about two thousand times smaller than that of chlorophyll 

 (the evidence can be found in the discussion about the photosynthetic 

 unit). 



Summing up, we may state that the heart of the photosynthesis 

 problem is the effective utilization of energy which has to be accepted 

 in a few big lumps. Franck and Herzfeld (4) calculate an immediate 

 and permanent gain of 21,000 calories for each quantum absorbed. 

 Does comparison with chemosynthesis point to an orthodox solution 

 of this problem? 



Possible Role of Energy- Rich Phosphale 



Recent research on the utilization of metabolic energy in living 

 cells had led to the discovery that this energy is handled in parcels 

 not surpassing 12,000 calories packed away in so-called energy-rich 

 phosphate bonds. Such phosphate bonds occur, for instance, in 

 substances like Lipmann's acetyl phosphate (11) which, for the purposes 

 of our discussion, may be regarded as stable for an indefinite period. 



Recently, Emerson, Stauff"er, and Umbreit (2) suggested "that 

 for each quantum of light absorbed one 'energy-rich' phosphate bond 

 (of ca. 10,000 cal./mole) is formed." There is no experiment or 

 observation new or old which requires such an assumption. The only 

 merit of this proposal, therefore, would lie in the complete analogy of 

 photosynthesis with synthesis by thermal reactions. Part of the energy 

 contained in the unstable first product formed in the photochemical 

 reaction, the tautomer mentioned above (4), would be stabilized by 

 conversion into a phosphate bond. The loss involved would be two- 

 thirds of the chlorophyll excitation energy. There is general agree- 

 ment among those who have considered carefully the theoretical 



40 



