PHOSPHORYLATION BY ISOLATED CIILOROPLASTS 345 



think this would applj' to your phosphorylation reaction. In comparing it with the 

 Hill reaction, phosphorylation should be favored by hinh chloroplast concentra- 

 tions. 



Rabinowitch: You obtain from a preparation containing 0.5 /xM chlorophyll 

 about 12 nM ATP in a half hour? 



Whatley: In a half hour you can get up to 20 /nM fairly consistently. 



Rabinowitch: Dr. Arnon suggested that it is unimportant — but I think it is 

 important — to have a quantitative idea of the relative rates of the phosphoryla- 

 tion reaction and of photosynthesis. It seems to me that the first is only a few 

 per cent of the second (assuming that, the production of three high-energy phos- 

 phates is the equivalent of the reduction of one carbon dioxide molecule). You 

 should not think that I am prejudiced against the phosphorylation reaction as 

 something closely related to photosynthesis. I only suggest that it is important 

 to know the relative rates. 



Whatley: The maximum observed rate of phosplior\lation is approximately 80 

 moles phosphate per mole chlorophyll per hour.* 



Rabinowitch : This is about 40% of normal photosynthesis, on the basis of a 

 single ATP per O2 molecule. 



Gaffron: I thought that oxygen jM-oduction was inhibited by phthiocol and 

 that, under the influence of this poison, phosphorylation replaced oxygen produc- 

 tion. However, from the rates you report, it appears that these are not necessarily 

 two competitive processes. 



Whittingham : Chloroplasts can give 300 to 400 moles O2 per mole chlorophyll 

 per hour in the Hill reaction. 



* Recently the maximum rate of photosynthetic phosphorylation which we 

 have obtained was increased from 80 to approximately 400 moles phosphate per 

 mole chlorophyll per hour. 



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