COMMENTS ON THE FUNCTION OF HAEM PROTEINS 



AS RELATED TO PRIMARY PHOTOCHEMICAL 



PROCESSES IN PHOTOSYNTHESISi 



Martin D. Kamen 



Graduate Departiiicnt of Biochemistry 



Brandeis University 



Waltham, Massachusetts 



It is a privilege to appear as a discussant following the presentation 

 by our distinguished colleague, Professor Robin Hill. Much of our 

 own work in recent years was prefigured in his classic memoir of 1939 

 on the chloroplast reaction, wherein he offered the suggestion that a 

 respiratory pigment might be intimately linked in a chemosynthetic 

 system coupled to the initial quantum absorption process in photo- 

 synthesis (12) . Since then, data have been accumulating and are now 

 sufficient to indicate that in the early phases of photosynthesis there 

 is a close relation between tetrapyrrolic chelates of iron present as 

 haem proteins on the one hand, and of magnesium, present as chloro- 

 phylls, on the other. There is neither time nor space to enter into 

 a detailed discussion of these data which for the most part are ade- 

 quately documented in the literature (13, 14), I wish only to call 

 attention to a possible mechanism for chemical coupling to the initial 

 quantinii absorption process which may be inferred, if it is granted 

 that chelates of iron and magnesium exist in close contact in the 

 photosynthetic apparatus, whether chloroplast or bacterial chromato- 

 phores. 



As we know from the voluminous literature on electron transfer 

 processes in systems containing conjugates or chelates of metal ions, 

 the presence of a macrocyclic resonating system may induce rapid 

 electron exchange between ions otherwise shielded by solvent (3, 

 8, 19, 7) . In all photosynthetic systems a situation exists in which 

 an efficient resonating macrocyclic system — porphyrin or a derivative 



' *Tliis is jMiblitation No. fi<) of the Graduate Depaitment of Biochemistry, 

 Brandeis University, Waltham, Massachusetts. Much of the work on which this 

 report is based has been supported by grants from the National Science Founda- 

 tion, the National Institutes of Health and the C. I". Kettering Foundation. 



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