344 F. R. WHATI;KY, M. B. AIJ-KX, P. T. ARNO\ 



On the basis of the evidence now available a tentative scheme for 

 photosynthetic phosphorylation is presented below: 



hv 



1 



21H]< H-0 >10| 



i 



FMX > vitamin K > aseorbate 



ADP + Pi ATP 



It is suggested that the light energy used for the photolysis of water 

 is converted to the pyrophosphate bond energy of ATP during the 

 transport of [H] to [0] via a series of electron carriers, of which three, 

 FMN, vitamin K, and aseorbate, have so far been identified. The 

 identity of the electron carriers beyond aseorbate is unknown, but 

 they may very likely prove to be components of a cytochrome system 

 (11-13). However, the independence of photosynthetic phosphoryla- 

 tion from molecular oxygen suggests that the typical cytochrome 

 oxidase is not involved. The relative positions assigned to FMN and 

 vitamin K in the "electron ladder" are tentative, and based solely on 

 pubhshed redox potentials (14). It is possible that their positions are 

 reversed in vivo (15). • 



Discussion 



Rabinowitch : What kind of illumination did you use? 



Whatley: Neon tubes containing a phosphor which gave predominantly red 

 light but had a fairly wide spectrum. 



Gibbs : Does ADP have any effect on the amount of phosphorylation? 



Whatley: No, you get the same results whether you use ADP or AMP as ac- 

 ceptor. 



Witt: What is the size of the broken chloroplasts? 



Whatley : These range from approximately a micron up to the size of the un- 

 t)roken chloroplasts. 



Clendenning: To observe the full capacity- for water photolysis in isolated 

 chloroplasts, you have to use as dilute suspensions as when measuring the photo- 

 synthetic capacity of Chlorella. There should be less than 0.1 mg. chlorophyll per 

 Warburg vessel. Most work on the Hill reaction refers to denser chloroplast 

 suspensions. Hill reaction rates per unit of chloroplasts or chlorophyll are about 

 150% higher with 0.1 mg. than with 0.5 mg. chlorophyll per vessel. But I don't 



