294 MARTIN D. KAMEN 



62. Williams, R. J. P., in " Intl. Sympos. on Haematin Enzymes" ed. R. Lemberg, 

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63. Arnon, D. I., Nature, Loud. 184, 10 (iqSQ)- 



64. George, P., and Irvine, D. H., in " Symposium on Co-ordination Chemistry", 

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Discussion 



Chance : This is a very exciting mechanism which Dr. Kamen has presented 

 and I am sure that it is just as he says : without speculation we can't get anywhere. 

 But I want to pull him back a little bit if I may because he has galloped off with 

 the wrong haem protein. I think this mechanism is intuitively based on RHP being 

 the initial electron donor and I think the initial electron donor is cytochrome c. In 

 studies of Chrotttatium even at temperatures of liquid nitrogen we observed on 

 illumination of the bacteria the disappearance of a band which has a peak at 

 420 m/x which suggests that the primary event involves a c-type cytochrome and 

 not RHP. 



Kamen: What I was actually talking about was oxygen evolution. In the 

 bacterial chromatophores, we do not have oxygen evolution so there is no necessity 

 to go to the higher valency states. You just start with the Fe- + and go to the Fe'' +. 

 I did say that the system produced in bacteria was not sufficiently electropositive 

 to produce the Fe* + state. One could suppose that if in green plants cytochrome 

 begins in the Fe^ + state, you won't see the change because it involves going from 

 Fe^ ^ to Fe*, whereas in the bacteria which are anaerobic, the steady state of the 

 cytochromes is predominantly Fe- +. The cytochromes would be reduced in the 

 dark, and when you add light you would go from the Fe- + to the higher valency 

 state, maybe even Fe* + for all I know, but certainly to Fe^ + and you would see 

 the usual difference spectrum. I should say that Dr. Chance's group has provided 

 the best evidence for this reaction in the bacteria by showing that it goes at liquid 

 air temperature. As regards the RHP question I should say that cytochrome r-type 

 proteins cannot be peroxidized to Fe* +. Philip George tried this with cytochrome 

 c : you take cytochrome c and add permanganate to it and all you get is destruction 

 of protein, unlike what happens with myoglobin, so I think this makes it improb- 

 able that cytochrome c is involved in the primary reaction. I think it must be some- 

 thing like RHP, or even something quite remote from a haem protein like man- 

 ganese. I don't think there is any way of telling at this time. I think we should be 

 looking for a myohaematin-type protein in green plants. There are catalases and 

 peroxidases present in chloroplasts and chromatophores. These may be the things 

 which are reacting in trace amounts, and, if they are you might never see a spectrum 

 corresponding to the reactions of these components but rather only the results 

 arising eventually from oxidation of cytochrome c. 



