ELECTRON TRANSPORT IN R. RUBRUM 



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RATIO 



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LIGHT 



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ETHYLENE GLYCOL (M) 



Fig. 3 . Effect of ethylene glycol on oxygen consumption by light-grown 

 cells of R. nihnitn. Experimental conditions were the same as for 

 Fig. 1, except that ethylene glycol was added as indicated (18), 



rose when the concentration of cyanide was increased from 10"^ to 

 10-3 M (Fig. 4). The light-insensitive respiration appeared to be more 

 cyanide- sensitive than the light-sensitive respiration. This indicates 

 that the system for oxygen uptake is at least in part different between 

 the light-grown and the dark-grown cells, and it is probable that the 

 light-insensitive respiratory system of the light-grown cells is the 

 same in kind but varies in activity from the respiratory system of the 

 dark-grown cells. 



Respiration of light-grown cells of R. ruhrum in growth medium 

 was hardly influenced by heating below 45 °C for 5 minutes (Table 1). 

 After heating at 50°C, the dark (total) respiration decreased approxi- 

 mately 20 per cent in rate, the light-insensitive respiration increased 

 approximately 30 per cent, and the light-sensitive respiration decreased 



