294 



ELECTRON TRANSPORT 



the maximal rates of photophosphorylation varied from one preparation 

 of washed chromatophores to another, the relationship between photo- 

 phosphorylation rate and ascorbate concentration remained unaltered 

 with either kind of chromatophores, active or less active. Under aerobic 

 conditions, the addition of 2 x 10"^ M oxidized cytochrome c^ lowered 

 the concentration of ascorbate required for maximal photophosphory- 

 lation from 5 X 10~2 M to 8x 10-3 m. The maximal rate of photophos- 

 phorylation was, however, not altered significantly. Apparently, the 

 addition of cytochrome c^ mimics anaerobic conditions. 



0^ 



O 



X 



o 



UJ 



Q- 



< 



J? 



o 



E 



2.0 



1.5 



1.0 



0.5 



0.0 



■t- RF( 6.7 X 10"'m ) 



+ NONE 



5 -A -3 -2 -1 



Log [ascorbate added. M ) 



Fig, 14. Effect of riboflavin (RF) on photophosphorylation in R. nibnon chro- 

 matophores. Experimental conditions were the same as for Fig. 12, except that 

 riboflavin was added as noted. Open symbols, in light (450 ft-candles); black 

 symbols, in darkness (43). 



Baltscheffsky (73) has reported that atabrine dihydrochloride (quina- 

 crine hydrochloride) remarkably inhibits the succinate-inducedphoto- 

 phorylation in chromatophores, and that the inhibition is neutralized 

 by the addition of a high concentration (mM order) of FAD, but not 

 FMN, He has claimed that FAD is functional in the photosynthetic 

 electron transport chain. As we have shown, when 7 x 10-5 m riboflavin 



