PHOTOOXIDATION AND PHOTOREDUCTION REACTIONS 241 



CYTOCHROME c 



Fig. 4. Photooxidation of reduced methylene blue and ferrocytochrome c by 

 R. ntbruDi chromatophores. The experimental conditions were those given for 

 Fig. 1, except that DPIPH2 was replaced with the oxidants listed. Ferrocyto- 

 chrome c was prepared by reduction with borohydride. When present, it was 5 

 mg per 8 ml and the BChl concentration was 0,190 mg. For the experiment in- 

 volving MB, 3.1 raM succinate was present initially to reduce the MB via the 

 succinic dehydrogenase contained in the chromatophore particles. Following 

 the enzymatic reduction of MB, sufficient fumarate was added to make the so- 

 lution 0.75 mM in fumarate. For this experiment the BChl concentration was 

 0.128 mg. 



place within the chromatophores themselves at this wave length. There 

 was no coupled reaction with either fumarate or NAD present in the 

 system. The inactivity of ferrocyanide in the present case is somewhat 

 surprising, since ferricyanide has been shown to interreact with bac- 

 terial chromatophores in two ways. Goedheer has shown that ferricy- 

 anide will cause a bleaching of bacteriochlorophyll in/?, rubnim, which 

 corresponds to an oxidation of the pigment (28). Calvin and Androes 

 have also reported that mixtures of ferro- and ferricyanide of different 

 redox potentials influence the photoinduced ESR signal observed with 

 chromatophores of R. nthniui (29). One possibility for the inactivity 

 of ferrocyanide in the present reaction is that it may be reduced as 

 rapidly as it is oxidized by the bacterial chromatophores. If the ferro- 

 cyanide must react through the cytochrome c^, whose standard redox 

 potential is below that of the ferrocyanide system, the resulting slow 



