THE EFFECT OF UBIQUINONE2 ON PHOTOPHOSPHORY- 



LATION IN PARTICLES OBTAINED FROM 



RHODOSPIRILLUM RUBRUM GROWN IN 



MEDIA CONTAINING DIPHENYLAMINEl 



HARRY RUDNEY 



Deportment of Biochemistry, School of Medicine 

 Western Reserve University, Clevclmid 6, Ohio 



It has previously been shown that cells of R. rubrum grown in the 

 presence of diphenylamine contain greatly reduced amounts of ubi- 

 quinoneio (coenzyme Qio)^ (1,2). Chromatophore particle preparations 

 from these cells (DPA particles) carry on photophosphorylation at a 

 lower rate than particles from normally grown cells. The DPA parti- 

 cles require a catalytic amount of a reductant in order to maintain 

 cyclic photophosphorylation. It was observed (2) that photophosphory- 

 lation in the presence of 1 mM succinate was greatly stimulated by the 

 addition of UQ2, however with lower concentrations of succinate (0.05 

 mM) addition of UQio completely inhibited phosphorylation. The stimu- 

 lation of photophosphorylation by UQ2 was completely abolished by 

 antimycin. 



Since reporting these results many experiments have been per- 

 formed to elucidate the site of these various effects. The results 

 were often puzzling in that it was soon found that depending on con- 

 ditions one could obtain either stimulation or inhibition of light- 

 induced photophosphorylation (LIP), and there was a great variation 

 between preparations. It gradually became clear that what we were 

 witnessing was the extreme sensitivity of the DPA chromatophore 

 system to changes in redox balance brought about by the various agents 

 added, i.e., there appeared to be very little poising capacity of the 

 redox systems in these preparations. These experiments will be fully 

 reported elsewhere but a few typical experiments shown in the follow- 

 ing tables will suffice to show that UQ2 can overcome the inhibitory 

 effect of antimycin merely by changes in the redox balance of the 



1 This investigation was supported in part by a Public Health Service Research 

 Career Program Award (GM-K-3-993-C3). 



2 The following abbreviations are used: UQio = ubiquinoneio, UQ2 = ubiqui- 

 none2, suffix indicating number of isoprenoid units in side chain; LIP = light- 

 induced phosphorylation; DPA particles - chromatophore particles from cells 

 grown in diphenylamine; PMS = phenazine methyl sulfate. 



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