408 DANIEL I. ARNON 



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Discussion 



Bergeron : The thiosulphate and light-driven fixation of nitrogen were not 

 cell-free extract studies, is that correct ? 



Arnon: Yes. 



Bergeron : Do you know how far the thiosulphate reaction is from the 

 chromatophores ? 



Arnon : The thiosulphate reduces the cytochromes of the chromatophores, so 

 it must be close. 



Allfrey : Is there any evidence that polynucleotides are involved here ? There 

 is a little RNA and perhaps a little DNA in the chloroplast. 



Arnon : There is nothing in our evidence to rule that out. 



Allfrey : Does ribonuclease affect any of these processes ? 



Arnon : It has not been tried. 



DiscHE: What is the relation between your non-cyclic phosphorylation and the 

 phenomenon which Ochoa and Vishniac describe. 



Arnon : The Vishniac and Ochoa system involved a collaboration between 

 chloroplasts and mitochondria. Chloroplasts reduced the pyridine nucleotide, 

 which then had to be given to mitochondria to carry out the phosphorylation 

 reaction. Thus the phosphorylation reactions proper were those of oxidative 

 phosphorylation by mitochondria. In photosynthetic phosphorylation no mito- 

 chondria are involved ; the chloroplasts do it themselves. In the Vishniac and 

 Ochoa phosphorylation by mitochondria oxygen is ro/WMwe</; in non-cyclic photo- 

 phosphorylation by chloroplasts you will observe that oxygen is produced. More- 

 over, in oxidative phosphorylation by mitochondria, DPNH2 is oxidized to DPN, 

 in non-cyclic photophosphorylation by chloroplasts it is just the reverse, TPN is 

 reduced to TPNH,. 



DisCHE : I would say that this leads to the question of the source of the hydro- 

 gen ; didn't Vishniac and Ochoa say that hydrogen came from water ? 



Arnon : There is no conflict between that statement and the experimental facts 

 of non-cyclic photophosphorylation. 



Dische: Have you any evidence that phosphorylation and reduction take place 

 in the same process ? 



Arnon: Yes, that is definite. It has been confirmed in several other laboratories. 



Dische: But I think that in the mitochondria TPN is not a good phosphoryla- 

 ting agent. 



