OXIDATION-REDUCTION REACTIONS IN 

 CHLOROPLASTSi,2 



Andre T. Jagendorf and Giorgio Forti 



McCollum-Pratt Institute and Biology Department 



The Johns Hopkins University 



Baltimore, Maryland 



We would like to point out that a very generalized scheme for 

 the photosynthetic reactions in isolated chloroplasts seems sufficient 

 to account for a large number of current experimental observations. 

 While the skeletal scheme in itself says nothing interesting about the 

 basic details of photochemistry in chloroplasts, at least it is useful 

 in defining the area in which a particular reaction or inhibitor par- 

 ticipates, under particular experimental conditions. 



The possible reactions resulting from the action of light might be 

 summarized by the five following equations: 



X + y + H.O 4- hv -^ XHo + YO (1) 



XH. + ^ -» ^H. + X (2) 



YO -> y + 1/2 O. (3) 



yo + AHo ^ y + ^ + H2O (4) 



AHo + 1/2 O2 -» ^ + H.O (5) 



Equation 1 is supj:)osed to represent the initial reaction caused by 

 light. According to most present speculations, light causes one cata- 

 lyst to achieve a highly reducing potential, and another to become 

 oxidized. In equation 1, this is indicated by the transformation of 

 an unspecified component X to XH2, and a component Y to yO. 

 Water is indicated to be a very early participant here, as suggested 

 by van Niel (27) and by Frank and Bruggcr (4) . Alternative 

 suggestions in which water is not an early participant (5, 15) and may 

 even be a terminal electron donor prior to oxygen evolution (1) 



' C'.otiliiljiitioii iiimibci 298 from the McColliiin IMatt Institute. 



- Original work dcsnibcd here was supported in part by grant RG 3923 from the 

 National Institutes of Health and in part by grant G 4379 from the National 

 Science Foundation. 



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