442 HERRICK BALTSCHEFFSKY 



of quantum efficiency is not quite the same thing as a direct measurement of the 

 number of phosphorylation sites. 



Baltscheffsky : I certainly agree that the quantum requirement experiments 

 only imply a ratio of two to one and that they do not give final proof for it. Re- 

 garding the possibility that phenazine methosulphate may act at two points, as 

 Dr. Jagendorf suggested ; as long as no experiments support such an idea it seems 

 logical to continue to assume that phenazine methosulphate provides only one 

 "by-pass" around "the physiological pathway". The valinomycin data which 

 were presented appear to be inconsistent with a view that the same two phos- 

 phorylation sites could be involved in the presence of phenazine methosulphate as 

 in its absence. Taken together with the two other types of evidence given, it seems 

 to us that the quantum requirement experiments motivate the hypothesis that you 

 have two phosphorylation sites in "the physiological pathway" and only one site 

 in "the phenazine methosulphate pathway". 



Williams: I just wanted to ask about valinomycin inhibition: you wrote it 

 on one of your schemes with the inhibited sites towards the reductant but did you 

 have any evidence on this point ? 



Baltscheffsky: No. 



Williams: You just had to put them somewhere ? 



Baltscheffsky: Yes, we had the phenazine methosulphate results and we had 

 to put in the valinomycin-inhibited step somewhere where phenazine metho- 

 sulphate ' ' by-passes ' ' the ' ' physiological ' ' electron transport chain in order to explain 

 the fact that we did not have an inhibition when this agent was added. The essential 

 point is really this : we have to do here with cyclic electron transport both in the 

 absence and in the presence of phenazine methosulphate. What our data indicate is 

 that one phosphorylation site is in the part of the "physiological pathway ", which 

 is shared by " the phenazine methosulphate pathway " and the other site in the part 

 which is "by-passed" by phenazine methosulphate. 



Arnon: I would like to associate myself with Dr. Baltscheffsky 's interpretation 

 of the phenazine methosulphate data as suggesting that there is probably more 

 than one phosphorylating site and that by using phenazine methosulphate we are 

 by-passing one of them. It seems to me that this is strongly supported by the 

 chemical evidence for the way phenazine methosulphate acts and I rely here on 

 the data of Dr. Massey. I am very impressed by how rapidly phenazine metho- 

 sulphate reduces cytochrome in his experiments. It is a very effective electron 

 carrier to cytochrome and this, taken together with the evidence from photo- 

 phosphorylation experiments gives me some confidence that this may be the 

 correct interpretation, namely, that in the presence of phenazine methosulphate 

 electrons go directly to cytochrome and by-pass any phosphorylation sites prior 

 to the cytochromes. 



