AEROBIC PHOSPHORYLATION IN R. RUBRUM 173 



It must be noted, however, that separation of most of the DPNH 

 oxidase from the phosphorylating system in dark extracts was some- 

 what unexpected. Previous work with similar extracts (1) repeatedly 

 had shown that DPNH oxidase, succinic dehydrogenase and the phos- 

 phorylation system sedimented together under the conditions of the 

 usual differential centrifugation. 



Preliminary experiments with crude photosynthetic extracts indi- 

 cate that the aerobic phosphorylation system sediments at a rate 

 similar to that of the chromatophore fraction. The data are consistent 

 with the concept that the aerobic phosphorylation system is associated 

 with the chromatophore fraction (11), Further proof of association, 

 however, must await results of purification of these particulate sys- 

 tems using other means. 



The aerobic phosphorylation system obtained in sucrose density 

 gradient experiments appears to be the same system observed pre- 

 viously in crude washed 145,000 x g particles obtained by differential 

 centrifugation (1), Both the latter particles and the active sucrose 

 fractions required DPNH for activity, giving P/2e ratios below 1; the 

 DPNH oxidase of both was amytal sensitive, but relatively unaffected 

 by antimycin A, 



The most interesting observation made in the study of the inhibition 

 of aerobic phosphorylation was that low concentrations of a potent 

 uncoupling agent (F3COCCP) were strongly inhibitory. This fact and 

 the sensitivity to oligomycin indicate that the mechanisms involved 

 in phosphorylation by this preparation may be similar to those of 

 other sensitive systems (6,8). 



SUMMARY 



1, Centrifugation in sucrose density gradients of crude extracts 

 of R. rubrum cells grown aerobically in darkness has shown that the 

 aerobic phosphorylation system is associated withheavy particles rich 

 in succinic dehydrogenase. The phosphorylation system is separable 

 from the bulk of the DPNH oxidase activity, which is associated with 

 light particles. 



2. Similar centrifugation experiments with crude extracts of photo- 

 synthetically grown R. rubrum indicate that the rate of sedimentation 

 of the aerobic phosphorylation system is similar to that of the chroma- 

 tophore fraction. Succinic dehydrogenase activity is also closely cor- 

 related with the chlorophyll content of the chromatophore fraction. 



3. The properties of the aerobic phosphorylation system in sucrose 

 gradient fractions are similar to those of the cruder systems previ- 

 ously studied. 



4. The effects of a variety of inhibitors of electron transport and 

 uncoupling agents of oxidative phosphorylation on the aerobic phos- 



