300 ELECTRON TRANSPORT 



photophosphorylation could be demonstrated with the washed chroma- 

 tophores prepared by grinding the cells with alkaline aluminum oxide 

 (Fig. 18) and appeared to be more or less uncoupled in the washed 

 chromatophores (showing negligible ATPase activity) which had been 

 prepared by the conventional method of sonication (Fig, 19), 



With R. rubrum, it was foiind that photophosphorylation in chroma- 

 tophores was inhibited in the presence of Triton x-100, a nonionic 

 detergent. Triton influenced the as corbate- induced photophosphoryla- 

 tion to a much greater extent than the PMS-induced photophosphory- 

 lation (Fig. 20), Antimycin A completely inhibited ascorbate-induced 

 photophosphorylation but not the PMS-induced photophosphorylation, 

 clearly indicating that the antimycin A- sensitive site in the electron 

 transport chain is by-passed in the presence of PMS. PMS-induced 

 photophosphorylation probably consists of phosphorylations at more 

 than one phosphorylating site, one of which is the same as the phos- 

 phorylating site (flavin level) of the ascorbate-induced photophosphory- 

 lation (43), It seems likely that the PMS-induced photophosphorylation 

 takes place also at the cytochrome c^ level. 



0.1 0.2 0.3 



TRITON X - I (%) 



Fig. 20. Effect of Triton X-lOO, nonionic detergent, on photophosphorylation 

 by li. rnbriini chromatophores. Experimental conditions were the same as for 

 Fig, 13, except that PMS or ascorbate was added at optimal concentration, and 

 the reactions were carried out in the presence or absence of antimycin A. 



