440 



LIGHT AND LIFE 



Rhodospirillum rubrum extract 

 Anaerobic extract 



Difference spectra of 

 illuminated nninus dark extract 



+O.OI5n I 



n 



+0.01- 



J +0.005H 



d 



< 



0- 



-0.005- 



no ADP 

 plus ADP 



P p 



reference 

 wavelengtti = 470 m>i 



1 — r 



400 



430 



460 



Fig 4. Changes in absorption spectrum of cell-free extract of R. rubrum in the 

 presence or absence of ADP. The extract was diluted with buffer (0.2 M glycylgly- 

 cine, pH 7.4) containing 0.01 M Mg++ and F" ions and 0.0067 M inorganic phos- 

 phate and 0.015 M succinate. Curve I shows the difference in absorption spectrum 

 between illuminated and dark extract in the anaerobic state. Then ADP was added 

 to the same mixture to a concentration of 0.0034 M and curve II was obtained, 

 which represents the difference between illuminated and dark extracts in the anae- 

 robic state when light-induced phosphorylation was taking place. 



diluted in buffer containing magnesium and phosphate ions results 

 in no oxidation ol cytochrome pigments (9) . A broad absorption 

 band appears around 434 m^ on illumination. The compound re- 

 sponsible for this absorption band is unknown, but it probably is 

 not involved in normal liglit-induced reactions (10) . When the same 

 particulate susj^ension is illuminated alter addition of a phosphate 

 acceptor (ADP) , a trough is seen in the illuminated minus dark 

 difference spectrum at 420 ny, indicating that the cytochrome c^ 

 becomes more oxidized on illinnination inuler conditions where light- 

 induced jihosphorylation is proceeding. This implicates the cyto- 

 chrome c-, in an electrou-transfer system which reacts during illumina- 

 tion to promote the phosj)horylation of ADP. Frenkel has shown that 

 substrates are not oxidi/ed timing this reaction (6) . There seems 

 to be obligate (()uj)liiig of the oxidation-reduction reactions involving 



