366 DANIEL I. ARNON 



TABLE IV 



Cyclic Photophosphorylation by Purified Ghana with and without added 

 Chloroplast Extract. Illumination 35 000 Lux 



(Miiller, Steere, and Arnon [118]) 



Treatment Q,?''* 



Phenazine methosulphate 157 



Phenazine methosulphate + chloroplast extract 145 



Vitamin Kg 39 



Vitamin K3 + chloroplast extract 78 



FMN 46 



FMN + chloroplast extract 6g 



* Micromoles orthophosphate esterified per mg. chlorophyll per hour. 



and vitamin K systems (Table IV) suggests that the extract contains some 

 chloroplast constituents that are involved in these pathways but not in the 

 pathway catalyzed by phenazine methosulphate. 



The close structural association, in both chloroplasts and bacterial 

 chromatophores, of the phosphorylating activity with the chlorophyll 

 pigments suggests that the harnessing of light energy in photosynthesis is 

 more closely associated with ATP formation than w'ith CO2 assimilation. 

 The enzymes responsible for COo assimilation are easily dissociable from 

 granaf in the case of chloroplasts [38, 39, 37], and not even structurally 

 joined together in the case of bacterial chromatophores [68, 121]. These 

 facts are in agreement with the view [94, 95] that in the course of bio- 

 chemical evolution, photosynthesis first emerged as a process for con- 

 verting light energy into ATP and this "primitive" photosynthesis 

 became only later a process linked to CO., reduction. 



10. Cyclic photophosphorylation as primitive photosynthesis 



In the conventional view of photosynthesis, the chemical energy 

 obtained by the conversion of absorbed light is always used for the reduction 

 of CO.,. The case that cyclic photophosphorylation is a "primitive" 

 photosynthesis in the evolutionary sense, would therefore be strengthened, 

 if examples could be found today of cases in which the contribution of 

 light to carbon assimilation could be experimentally limited to the 

 formation of ATP. 



t Grana, as contrasted with whole chloroplasts, cannot assimilate CO., to the 

 level of carbohydrates but retain a capacity for photochemical oxygen evolution 

 and photosynthetic phosphorylation. These findings do not exclude the catalytic 

 participation of CO. 2 in the mechanism of oxygen evolution as has recently been 

 proposed by Warburg et al. (Z. Natio[f. 14b, 712-724, 1959). 



