292 



ELECTRON TRANSPORT 



PHOTOPHOSPHORYLATION COUPLED WITH PHOTOSYNTHETIC 

 ELECTRON TRANSPORT SYSTEM 



Earlier, Gest and Kamen (68) demonstrated that illumination greatly 

 accelerates both the uptake of Pi32 by intact cells of R. nibriim and the 

 turnover of Pi between soluble and insoluble cellular fractions. Fren- 

 kel (69) was the first to clearly demonstrate light-induced phosphory- 

 lation by cell-free preparations (chromatophores) of photosynthetic 

 bacteria. He found (70) that the washed chromatophores actively 

 esterify Pi in the presence of ADP or IDP but not with AMP or IMP. 

 ADP generally appeared to be a better acceptor than IDP. 



Photophosphorylation by bacterial chromatophores appears de- 

 pendent on catalytic amounts of reductants (37,71). A number of ex- 



1.2 



1.0- 



0.8 



Q 



^ 0.6 

 o 



0.4- 



0.2- 



0.0 



LOG (ASCORBATE ADDED, M) 



Fig. 12, Effect of cytochrome c 9 on photophosphorylation by /?. n/ftr?//;? chroma- 

 tophores. ATP formation was followed by measuring the radioactivity incorpor- 

 ated from Pi32 into ATP in the presence of ADP. Standard components of the 

 reaction mixture were as follows: Tris-sucrose buffer (0.2 M, 10% pH 8.0), 

 0.50 ml.; 0.1 M MgCl2, 0.10 ml.; 0.1 M Pi32 solution (pH 8), 0.10 ml.; 0.1 M 

 ADP solution (]3H 8), 0.10 ml.; suspension of washed /?. rnhrnm chromatophores 

 (S) (Aygo m^/n^l-» approx. 50), 0.10 ml.; total volume adjusted to 1.50 ml. by 

 addition of the buffer. In some cases a fixed concentration of oxidized cyto- 

 chrome C2 (2 X 10~5 m) was present. Open symbols, in light (450 ft-candles) 

 (43). 



