DISCUSSION 445 



oxidation to the cytoclirome chain, and in fact we expected something like 

 phosphorylation (which we managed to prevent ourselves Irom finding by 

 clever reasoning!!) . I wish to give Dr. Vernon some credit for the fact that 

 he introduced me to cytochromes. I do not know whether this was a good 

 idea or not. As he has not been mentioned very much in this symposium 

 I feel it imperative to say that it was his work with Alberty and Mahler on 

 cytochrome c reductase which began all this. Now until recently, Dr. Hill 

 and I were the only ones that talked about cytochromes in photosynthetic 

 systems, so it is very gratifying to sec the tremendous amount of interest 

 which is now developing in these pigments. It is not so gratifying to see 

 what little work is being done on them. I must emphasize that we will 

 have no conception of what these are doing in photosynthesis unless we 

 isolate them and determine their physico-chemical properties. And in this 

 connection, what Dr. Arnon said about nomenclature comes up. Ihe term 

 cytochrome has been battered about in a rather glib way. It should be 

 emphasized that the cytochromes we are talking about in the photosynthetic 

 chain are not the cytochromes that are present in mitochondria. In at 

 least three or four instances in which we have gone to the trouble of isolating 

 and crystallizing and determining something about the structure of these 

 proteins, we find we do not have anything like the kind of cytochrome in the 

 respiratory chain. 



Dr. Wald: How can a thing be reduced by molecular hydrogen without 

 combining with it? 



Dr. Kamen: I did not mean to imply no combination. I meant that there 

 is no combination without reduction. 



Dr. Wald: Is not that a pretty unusual reaction you have in your scheme 

 with molecular hydrogen? 



Dr. Kamen: There are hydrogenases present. 



Dr. Wald: Isn't RHP one of the hydrogenases? 



Dr. Kamen: No. RHP is not a hydrogenase. There is a special hydrogenase 

 enzyme in Rhodospirilhim rubrnm which can be extracted and purified and 

 which appears to be the mechanism for the introduction of hydrogen as a 

 hydrogen donor in the photosynthetic process. 



Dr. Rabinowitch: I am glad that someone goes beyond the "ordinary" 

 cytochromes, and "ordinary" TPN and thinks of "super-cytochromes" with 

 an oxidation potential permitting them to oxidize water, and of "super- 

 TPN" with a potential permitting it to reduce TPN. But if so, how do 

 you know that the oxidant is an iron complex, and not something altogether 

 different? 



Dr. Kamen: Why, indeed? I would like to make a plea that people stop 

 for the moment and work hard on the molecular analysis of chloroplasts 

 and chromatophores. There are many crucial problems in photosynthesis 

 which have not been solved yet. One is, what is in the chloroplasts? and 

 what is in tlie diromataphore? Except for tlie state of knowledge back iii 



