ELECTRON TRANSPORT IN R. RUBRUM 285 



In view of its high autoxidiz ability (29), it is supposed that RHP 

 (cytochrome o) is functional as an oxidase in respiration of R. rubrum 

 as well as in the nonphotosynthetic hsicterium. Micrococcus pyrogenes . 

 On the other hand, Bartsch and Kamen (30) have purified RHP from 

 the photo autotroph Chromatium, which never grows aerobically. It may 

 be, therefore, rational to consider that RHP has another anaerobic 

 function, perhaps as one of the oxidation- reduction components in the 

 photosynthetic electron transport system. 



In the action spectrum on the light relief of carbon monoxide- 

 inhibited respiration of dark-grown cells, the absorption peaks which 

 correspond to those of the complex of typical cytochrome oxidases 

 with carbon monoxide are not seen (31,32,33). This indicates that the 

 cytochrome oxidases, if present, are not functional. This indication 

 may apply to respiration of light-grown cells which show a lower res- 

 piratory activity, in good accordance with Smith (34). 



ELECTRON TRANSPORT SYSTEM 



Chromatophores from R. nibrum catalyze a reduction of cyto- 

 chrome C2 in its oxidized form by appropriate substrates such as 

 succinate. This bacterium contains succinic dehydrogenase (19,35) and 

 coenzyme Qj^q (Rudney, H., and Sugimura, T., quoted by Sugimura and 

 Okabe (36)). It was found that cytochrome Cq reduction by succinate 

 with chromatophores was completely inhibited in the presence of a 

 low concentration (10 y/ml) of antimycin A. Geller and Lipmann (26) 

 have found that photophosphorylation in chromatophores is antimycin 

 A sensitive. Sugimura and Okabe (36) have reported that the coenzyme 

 QlO present in chromatophores is reduced by succinate. Geller (37) 

 has reported that the photophosphorylation induced in the presence of 

 phenazine methosulfate (PMS) is hardly influenced by antimycin A, 



Although all attempts to disrupt chromatophores into active but 

 much smaller fragments with the use of some detergents (digitonin, 

 cholate, and Triton x-100) have failed, it was noted that cytochrome 

 C9 reduction by succinate in darkness was inhibited in the chromato- 

 phores which had been treated with an appropriate concentration of 

 Triton x-100, in the same manner as ascorbate-induced photophos- 

 phorylation (below) in the chromatophores with antimycin A. According 

 to current considerations on the antimycin A- sensitive site in the mito- 

 chondrial respiratory system, the coenzyme Qio present in chromato- 

 phores may be the site sensitive to antimycin A as well as Triton x-100. 



From cells of R. nibrum. RHP and cytochrome c 9 have been ex- 

 tracted in a water-soluble state and purified (38.39) to crystalline 

 states (40). Both heme proteins have been characterized in detail (29, 

 40,41,42), and their Eg has been determined to be +0.31 V for cyto- 

 chrome C2 (39) and -0.01 V for RHP (29). Horio and Kamen (43) de- 



