DANIEL I. ARNON 



517 



Ogata, ami Anion (IM). The absorption spectrum ol the reduced 

 form ol a jnnifietl cytochrome c, from our preparations (Fig. 6) is 

 the same as that described by Bartsch and Kanien (23) . 



The effect of Hght on the absorjjtion spectrum (cHffcrence spec- 

 trum, light minus dark) of cytochromes in cell-free preparations of 

 Chrornatium is shown in Fig. 7. On illumination, the absorption 

 spectrum of cytochromes shows oxidation followed by a reduction in 

 the dark and reoxidation upon repeated illumination. Under the ex- 

 perimental conditions in which the Chromatiiim cell-free system was 

 investigated, the light-dark reversible oxidation-reduction reactions 



Reversible oxidation of Chrornatium cytochromes by light 



(P*S) 



O.lr 



K 



I 



0.05 

 



-0.05 - 

 -0 1- 



0.05 

 



-0.05^ 



0.1- 



0.05- 







420 



-0.05- 



-0.1 



0.05 



O 



-0.05 



420 



522^ 

 552 



LIGHT 



DARK 



522\I 



LIGHT 



552 



DARK (D-D) 



400 450 500 550 600 



Fig. 7. Successive oxidation by light and reduction in the dark of cytochromes in 

 cell-free preparations of Chrornatium. The reaction mixture included in a final 

 volume of 3.0 ml, chromatophores (P) containing 0.06 mg bacteriochlorophyll and 

 supernatant fluid (6) corresponding to 0.5 mg bacteriochlorophyll. A small amount 

 of NaoS.Oi was previously added to S, which was then dialyzed against 0.2 M tris 

 buffer, pW 7.8, prior to use. The reaction was carried oiu at room temperature. 

 Gas phase, argon. Difference spectra, using the dark treatment as control, were made 

 in Thunberg type cuvettes, with a Gary recording spectrophotometer. Illumination 

 was by a tungsten lamp (35,000 Lux). (Nozaki, Ogata, and Arnon, 114). 



