246 ELECTRON TRANSPORT 



CHARACTERISTICS OF THE DPIPH2 PHOTOOXIDATION 

 SYSTEM OF R. RUBRUM CHROMATOPHORES 



From the extent of the fast reaction observed with both R. nibnim 

 and Chromatiiim, it is possible to calculate the amount of DPIPH2 

 converted in the photooxidation reactions. Table 1 presents the results 

 of such calculations, showing that for R. nibnim there is one mole of 

 DPIPH2 oxidized for every 6 moles of BChl contained in the chroma- 

 tophore. The value for Chromatiiim is approximately one mole of 

 DPIPH2 oxidized for each 7.5 moles of BChl. A logical compound to 

 consider as the intrachromatophoral oxidant for DPIPH2 is ubiquinone, 



TABLE 1. 



Ratio of BChl molecules to DPIPH2 photooxidized by 

 chromatophores. The experimental conditions for 

 R. rubrum were those given for Fig. 1, with only slight 

 variation in BChl content amojig the different experi- 

 ments. The experimental conditions for Chromatiiim 

 were the same as those given for Fig. 7. 



BChlA)PIPH2 



R. rubrum 



Average of 57 samples 5.9 



Chromatium 



Average of 5 samples 7,5 



This compound is present in chromatophores of both Chromatium and 

 R. rubrum in high concentrations. Fuller et al. have reported a ratio 

 of about five for chlorophyll to ubiquinone in Chromatium (32). Lester 

 and Crane (33) have reported a value of 4.3 /imoles ubiquinone per 

 gram dry weight for R. rubrum, which compares with 2.9 for Chroma- 

 tium. Nishimura (34) has recorded a value of 19 for the ratio of chloro- 

 phyll to cytochrome in R. rubrum. When this ratio is coupled to the 

 information presented byOeller (35) on the heme protein and ubiquinone 

 content of R. rubrum chromatophores, a ratio of about three chloro- 

 phylls to one ubiquinone can be calculated. Thus, there is sufficient 

 ubiquinone present in the chromatophores to account for the observed 

 photooxidation of DPIPH2 and TMPD in the absence of added external 

 oxidants. The succeeding paper presents definite evidence that ubi- 

 quinone is reduced as a function of added DPIPH2 with /?. nibnim 

 chromatophores. Clayton (22) has previously presented evidence that 

 a photoreduction of ubiquinone is a primary event following light ab- 



