Photosynthetic Phosphorylation and the Energy 

 Conversion Process in Photosynthesis* 



Daniel I. ARxoxf 



Laboratory of Cell Physiology, University of California, 

 Berkeley, Calif., U.S.A. 



I. Photosynthesis outside the Hving cell 



It is fitting to recall in a symposium devoted to biological structure and 

 function, that understanding of life phenomena at a molecular level was 

 always advanced by the separation of a physiological process from the 

 structural complexity of the living cell. This happened first for fermenta- 

 tion when Biichner in 1897 prepared from yeast a cell-free juice that 

 fermented sugar [2]. The most recent example is the cell-free synthesis of 

 DNA by Romberg [3], a development which demonstrated that the key 

 events in reproduction can be investigated with isolated enzyme systems. 



With regard to photosynthesis, in 1953 Rabinowitch wrote that "the 

 task of separating it from other life processes in the cell and analyzing it 

 into its essential chemical reactions has proved to be more difficult than 

 was anticipated. The photosynthetic process, like certain other groups of 

 reactions in living cells, seems to be bound to the structure of the cell; it 

 cannot be repeated outside that structure" [4]. 



There was no special reason why, at that late date in the development 

 of biochemistry, photosynthesis could not be reconstructed outside the 

 living cell. The simplest explanation for the repeated failures was that 

 inappropriate experimental methods had been used for this task in different 

 laboratories, including our own [5]. A continuing search for improved 

 experimental methods appeared therefore woith while. 



The most hopeful possibility for isolating photosynthesis from the 

 structural complexity of the whole cell seemed to lie in chloroplasts. Few- 

 physiological processes have such an obvious relation to a distinct cellular 

 particle as photosynthesis has to chloroplasts. In all plants which have 

 chloroplasts, not only do these particles contain all the chlorophvll (and 

 the accessory pigments) without which photosynthesis cannot proceed, 



* This article is based on a paper presented at the Symposiuni on "Light 

 and Life", at Johns Hopkins LTniversity, March 28-31, i960 [i]. 



t Aided by grants from the National Institutes of Health and the Office of 

 Naval Research. 



