I06 SUBCELLULAR PARTICLES 



system in chromatophores of photosynthetic bacteria (31), a system later found 

 also by Nieman and Vennesland in green plant chloroplasts (23). This reaction 

 required oxygen and did not occur anaerobically when exogenous hydrogen ac- 

 ceptors other than oxygen were added. From evidence gathered in studies on 

 simultaneous photo-oxidation of ethanol and ascorbate by both plant chloroplast 

 preparations and bacterial chromatophores, it was adduced that the photo-oxida- 

 tion of the cytochrome c, or of any cytochrome c substitute such as 2,6-dichloro- 

 phenolindophenol, was the resultant of two simultaneous photo-oxidations (32). 

 One of these involved the action of oxygen as a Hill reagent, the other involved 

 utilization of the photochemical oxidant itself. Thus, if we denote by [H] the 

 photo-reductant and by [OH] the photo-oxidant, then a series of reactions of the 

 following type could be visualized: 



/) 2HOH^^^2|H]+2[OH] 



2) 2[H]+0, >'HoO,' 



S) 'H2O2' + 2H^ + 2Fe+- Cyt > 2Fe+^ Cyt + 2H0O 



4) 2[OH]+2H+2Fe^-Cyt >2Fe^2 Cyt + 2HoO 



The over-all reaction would be: 



4Fe+- Cyt + 4H^ + O, > ^Fe'- Cyt + 2H.O 



as required by the stoichiometry established experimentally (32). 



This scheme was based on the specific requirement for oxygen as a Hill reagent 

 for trapping [H], and the experimental failure to separate [H] and [OH] under 

 anaerobic conditions. In 1954, however, Frenkel, using the same experimental 

 system {R. rubrum chromatophores), showed that a light-activated phosphoryla- 

 tion occurred under strictly anaerobic conditions (10). A similar observation was 

 made by Arnon and co-workers at about the same time, using green plant 

 chloroplast preparations ( 4 ) . These results could be interpreted to indicate suffi- 

 cient separation of photo-oxidant and photo-reductant to support anaerobic oxida- 

 tive electron transport reactions in which coupled phosphorylation could occur. 

 A similar photo-activated phosphorylation was demonstrated somewhat later using 

 the chromatophores from the strict anaerobes Chromatium and Chlorobium ( 19, 

 20). 



Earlier, Gest and Kamen (13) had demonstrated that illumination greatly ac- 

 celerated the uptake of inorganic phosphate (P^--labeled) by intact cells of 

 R. rubrum, incubated anaerobically, and also the turnover of phosphorus between 

 soluble and insoluble cellular fractions. These effects of illumination were no 

 doubt the result of the photo-activated phosphorylation later observed by Frenkel 

 and others in chromatophore preparations. It appears that photophosphorylation 

 is the experimental realization in cell-free systems of the process of coupled phos- 

 phorylation postulated in the schemes of Ruben, Lipmann, and others. If we add 



