LUCILE SMITH 



441 



cytochrome r^ and the i)Iiosphorylation system. Krogman et al. have 

 also sho^\•n evidence of obligate cou[)ling of phosphorylation and 

 electron transport in chloroplasts (7) . 



There is additional evidence (9) for the existence of two electron- 

 transport chains in R. rubrum, one being the respiratory chain sys- 

 tem which can oxidize substrates with oxygen and a second chain 

 which is involved in phosphorylation of ADP on illumination. The 

 two chains of oxidative enzymes show different reactivities on addition 

 of substrates or inhibitors; these effects are summarized in Tables 

 1 and 2. 



The scheme presented in Fig. 5 pictures the simplest systems which 

 woidd explain our observations on the photosynthetic bacteria (9) . 

 It includes two cytochrome chains, one of which is the respiratory 



TABLE 1 



Respiration and Light-induced Phosphorylation in Extracts 



OF Rhodospirillum rubrum 



Substrate 

 added 



Dark respiration 29.7° C 



lA Oil ^Moles/ 



hr X Dsoo hr X Dsoo 



Light-induced 



phosphorylation 



28° C 



Oxidative 



phosphorylation 



in dark 



TABLE 2 



Effect of Inhibitors on Respiration and Light-induced Phosphorylation 

 in Extracts of Rhodospirillum rubrum 



Inhibitor 



Concentration 

 of inhibitor 



Respiration in dark 

 per cent inhibition 



Light-induced 



phosphorylation 



per cent inhibition 



no added 

 substrate 



succinate 

 20 mM 



no added 

 substrate 



succinate 

 20 mM 



* Data on cyanide inhibition of respiration are erratic. Unless acetate is also present 

 with the succinate, sometimes 10"^ M cyanide is more inhibitory than 10 ' M. Possibly 

 keto acids, formed in the absence of acetate, will bind cyanide. 



