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ELECTRON TRANSPORT 



minimum to 280 m^u when DPIPH2 is present in the illuminated chroma- 

 tophore suspension. 



The kinetics for the absorption changes at three important wave- 

 lengths have been determined and the results are shown in Fig, 3. A 

 comparison is made between a system containing only chromatopho res 

 and one containing chromatophores plus DPIPH2, At 600 m^u the 



TIME 



16 SEC. 



< ► 



Fig. 3. Kinetics of the light-induced absorption changes observed with R. 

 ruhrum chromatophores in the absence and presence of DPIPH2. Experi- 

 mental conditions were the same as for Fig. 2, except that only one tungsten 

 lamp was used for illumination, and a No. 2600 Corning filter was used to 

 filter the actinic light. Corning filters were positioned in front of the photo- 

 tube opening for the experiments run at 275 (No. 9863) and 430 m/i (No. 4784). 



chromatophores alone show a decrease in absorbancy; with DPIPH2 

 present, the rapid photooxidation of this reduced dye is shown by the 

 increase in absorbancy. When the light is turned off, a slow decay or 

 back reaction of the DPIP takes place. It is evident, however, that the 

 intrinsic changes associated with the chromatophore component are 

 faster than those associated with DPIPH2 oxidation. 



The experiments performed at 430 m// show that the presence of 

 DPIPH2 results in a greater increase in absorbancy upon illumination 

 and also a much faster decay time for the absorbancy difference. The 



