512 



LIGHT AND LIFE 



cytochrome c is rapidly reduced in a non-enzymic reaction with re- 

 duced phenazine methosulfate. In Fig. 5, the intermediary electron 

 carrier is vitamin K or FMN. 



The cyclic electron flow diagrams, illustrated by Figs. 4 and 5, 

 are components of the scheme presented earlier (9) . The key reac- 

 tion in the proposed mechanism, the photooxidation of chlorophyll 

 by the loss of an electron, is based on a type of reaction in photo- 

 chemistry that was experimentally documented by Lewis and Lipkin 

 (91) . They found, by illuminating a variety of substances in rigid 

 media, "that one of the commonest photochemical processes is the 

 mere loss of an electron by an activated molecule" (91) . The evi- 

 dence for the then (in 1942) "new and somewhat surprising phe- 

 nomen" (91) was, for example, "that chemical oxidation at room 

 temperature and photooxidation at liquid air temperature (of tri- 

 p-tolylamine) have given the same substance, namely, the positive ion 

 left, (P-CH3-C0H4) 3 N+, when one electron has been removed" (91) . 



In the reactions studied by Lewis and Lipkin the fate of the ejected 

 electron was uncertain but, as they pointed out, "the electron must 

 lie in a potential hole which is deep enough so that the large electro- 

 static field of the ion is unable to dislodge it" for a considerable period 

 of time. This was indicated by the fact that "the [blue] color (of 

 the 'odd ion' formed) persists at liquid air temperature for several 





"^Cof actor 



ADP 



LIGHT ~P-^DP — nATP, 



Anaerobic cyclic photophosphorylation 



Fig. 5. Scheme for anaerobic cyclic photophosphorylation catalyzed by vitamin 



Ko or TMN. Details in the text. 



