CHLOROPHYLL-SENSITIZED REACTIONS in vilro 29 



TPN. Actually, we don't get by with just transferring four electrons. We have 

 to transfer six or seven electrons and need six or seven quanta. 



Rabinowitch : For that you have to have a process which would liberate energy 

 after these transfers. Do you want to leave this just to the decomposition of hy- 

 tlrogen peroxide? 



Bassham : That is s{)ontaneous. 



Rabinowitch : It evolves energy. Are you going to salvage this energy somehow? 



Bassham : No, we don't need it. 



Rabinowitch : For reduced TPX you really need some more energy to shoulder 



it up. 



Bassham : We do get that energy when we bvu-n part of the TPNH oxidatively. 



Rabinowitch : All right, so that would take care of itself, but the fundamental 

 process, the transfer from the level of water to hydrogen, i.e., the level of TPiS'H, 

 requires almost a full quantum itself. 



Duysens: In one absorbed quantum you have 40 kcal. Of course, a certain 

 amount is lost to form stal)le compounds. Let's say 8 kcal. Then you have 32 

 kcal. left for reduction of DPX. Transfer of one hydrogen from water to DPN re- 

 quires only 26 kcal. So I think it is possil)le. 



Rabinowitch : You will have just a very little left. It is just barely possible. 



Strehler: If you form peroxide as an intermediate you lose another 9 kcal. 

 which are not available for the formation of a potent reductant. 



Kamen; This is anticipating the argument that I expect tomorrow. The picture 

 that Dr. Bassham has been giving here is very similar to the one that we have 

 been trying to work out in connection with the interaction between chlorophyll 

 and cytochrome. But my feeling is that this discussion is fruitless and we will get 

 nowhere, for the simple reason we are not dealing with pure chlorophyll in photo- 

 synthesis. If you put this chlorophyll molecule on protein, I will venture to say 

 that all these energy requirements will disappear or be changed so that you will 

 have a different picture entirely. Until we find out something about native chloro- 

 phyll and about the biological capacity of it, I think we should postpone all 

 energy considerations entirely. 



What I am saying is that the cooperative pigment part of the assembly takes 

 up energy which is distributed over a large molecule, the sink of which we don't 

 know. The sink may not be the triplet state at all. It may be a double bond some- 

 where else. It may very well be (I say this with great hesitation) an iron hematin. 

 These are present in great amounts and can do everything that is needed in photo- 

 synthesis, as you will see tomorrow. 



There are so many processes that are impossible from a strictly physicochemical 

 standpoint but which occur all the time in biological systems, that the argument 

 that something cannot happen because 7 or 8 kcal. are lost is just plain senseless. 

 I think the best thing to do is to table the whole argument and not waste any 

 more time. 



Brugger: Dr. Franck, I think, certainly never denied any electron transfer 

 processes, but I think he felt if you used photochemistry to move electrons around 

 you had to pay some price. Since you had to do it in a short time you had to use 



