306 DOUGLAS C. PRATT, ALBERT W. FRENKEL, AND DONALD D. HICKMAN 



Vernon : I can give you some information about the relation between phos- 

 phorylation and photoreduction reactions. In our laboratory we have followed 

 photophosphorylation, the photoreduction of DPN and the photo-oxidation of 

 ascorbate. In the experiments we have performed, there is a large degree of 

 independence between these reactions. The photoreduction does not require an 

 associated phosphorylation and the photophosphorylation does not require an 

 associated photoreduction of DPN. This supports your idea that these two 

 reactions are separate and distinct. 



Frenkel : I believe in your paper on pyridine nucleotide reduction you men- 

 tioned that ADP and ATP inhibited reduction. Did you find that simultaneous 

 phosphorylation will inhibit the reduction ? 



Vernon : No, they are essentially independent. 



Arnon : I would like to state that we now have some evidence for non-cyclic 

 photophosphorylation in photosynthetic bacteria, that is coupled with the reduc- 

 tion of DPN. As in chloroplasts, non-cyclic photophosphorylation in bacteria, 

 does not replace cyclic photophosphorylation but supplements it. 



Frenkel: In the work of Smith and Baltscheffsky light-induced phosphoryla- 

 tion by Rhodospirillum chromatophores was shown to be linked to the oxidation of 

 cytochrome c and possibly also to the reduction of a 6-type cytochrome. 



Arnon: I am speaking of new evidence. It is perhaps premature to make the 

 comment before the evidence is presented but I wish to make it now for the sake 

 of completing the record of this discussion. 



