623 



Thomas Punnet t 



In summary, the accumulated evidence suppor 

 phosphorylating site in the Hill reaction syst 

 supported by these data is that the practice o 

 for the "control" rates clearly leads to value 

 unacceptably high. It may be proper to correc 

 rate found in the absence of all three phospho 

 P04= rather than in the absence of ADP (12) . 

 much smaller and would probably have the effec 

 ratio from 0.80 to 1.0. In either case, this 

 limit . 



ts the view that there is one 

 em. A second conclusion 

 f correcting the reduction rates 

 s of the ATP/2e- ratio that are 

 t the reduction rate for the 

 rylation reagents, ADP, Mg-H- and 

 If so, the correction would be 

 t of increasing the ATP/2e- 

 ratio still approaches one as a 



100 



Fig. 4- Relative rates of cyclic and non-cyclic phosphorylation 

 as a function of light intensity. 



There may be two or more phosphorylating sites in the electron transport 

 system of the chloroplast, but they are still hypothetical at the moment. Up 

 to the present time, the experimental evidence given in support of the two 

 site hypothesis can be explained in other ways. If a second phosphorylation 

 site exists in chloroplasts , a different kind of experiment will be needed to 

 demonstrate its presence convincingly. 



This work was supported by a grant from the National Science Foundation 

 (G- 14337) and a grant from the Charles F, Kettering Foundation. 



