244 



ELECTRON TRANSPORT 



data obtained with Chromatmm chromatophores. In the absence of 

 added oxidants, an initial fast reaction was observed. Although the rate 

 of the reaction was less than that observed with R. nibnim, the back- 

 reaction was faster than that observed with R. rubrum. The slower 

 initial photooxidation rates may merely reflect the fact that a faster 

 back-reaction obtains with these bacterial particles. 



The most significant difference observed between R. nibnim and 

 Chromatium lies in the fact that the latter particles are unable to 

 couple the photooxidation of the reduced dye with either fumarate or 

 NAD reduction, as shown in Fig. 7, To further check on this problem, 

 corollary experiments were done in which NAD reduction was attempted 

 in the presence of either succinate or ascorbate-DPIP, which systems 

 were designed for detection of NADH accumulation. All experiments 

 of this nature were negative. 



Chromatium chromatophores were tested for their ability to photo- 

 reduce methyl red, which is active in the photo reduction system of R. 

 rubrum chromatophores (17). Fig, 8 shows that Chromatium chroma- 

 tophores were able to photoreduce this dye, although the observed rate 

 was less than that obtained with R. rubrum. All indications point to a 

 relatively simple system being involved in the photo reduction of methyl 

 red and tetrazolium blue in the presence of the ascorbate-DPIP couple. 

 As shown below, this activity in the case of R. rubrum chromatophores 

 is more stable than is the NAD or fumarate reducing systems. 



I 2 3 4 5 



MINUTES 



Fig. 8. Photoreduction of methyl red by R. rubrum 

 and CliroiiiatiKiii chromatophores. The experimental 

 conditions given by Ash et. al. (17) were employed. 

 The BChl concentrations were 0.20 for R. ruhruiii and 

 0.20 for Cliro)iiot//tii, for the 8 ml reaction system. 



