240 



ELECTRON TRANSPORT 



.5 - 



LIGHT OFF 



NAD 



+ FUMARATE 



LIGHT ON 



2 3 4 



MINUTES 



Fig. 3. Photooxidation of TMPD by R. rubnan chromatophores. The 

 experimental conditions were as given for Fig. 1, except that 0.1 mM 

 TMPD was substituted for DPIPH2. The BChl concentration was 0.196 

 mg in the 8 ml reaction system. 



the system. Illumination in this case resulted in a fast reaction fol- 

 lowed by a secondary slower reaction which was coupled to the photo- 

 reduction of the added fumarate. When the light was turned off, a bi- 

 phasic reaction was observed. The initial fast back-reaction can be 

 correlated with reduction of methylene blueby the reduced components 

 in the chromatophore, while the secondary back- reaction is due to the 

 enzymatic reduction of methylene blue by the succinate present in the 

 system. 



In the case of ferrocytochrome c, a reaction was observed in the 

 absence of added oxygen, but the initial reaction was slow and the 

 extent of the reaction was less than that observed with DPIPH2. In this 

 case also, a coupled photooxidation could be obtained when fumarate 

 was added to the system. These reactions observed are in agreement 

 with the data on photooxidations previously reported (4), but the present 

 experiments show there are two phases for the photooxidation of both 

 these compounds. 



The response of ferrocyanide in the R. riibrum chromatophore 

 system was examined, and the results of this experiment are shown in 

 Fig. 5. Although some absorbancy change was noted when the system 

 was illuminated, this was largely due to absorbancy changes which take 



