EFFECT OF REDUCED 2,6-DICHLOROPHENOLINDO- 



PHENOL UPON THE LIGHT-INDUCED ABSORBANCY 



CHANGES IN RHODOSPIRILLUM RUBRUM 



CHROMA TOPHORES: A COUPLED 



REDUCTION OF UBIQUINONE 1 



HOWARD BALES and LEO P. VERNON 



Charles F. Kettering Research Laboratory, 



Yellow Springs, Ohio 



The light-induced absorbancy changes in the photosynthetic sys- 

 tem of Rhoclo spirillum rubrum have been investigated extensively. 

 Whole cells of R. rubrum have been investigated by Duysens (1), 

 Chance and Smith (2), and Smith et al. (3,4). Experiments with cell- 

 free extracts or chromatophores from R. n^6rzY;» have been performed 

 by Smith and Baltscheffsky (5), Clayton (6), and Nishimura (7,8), In 

 general, the absorbancy changes noted can be correlated with three 

 classes of compounds contained within the chromatophore, i.e., the 

 various forms of bacteriochlorophyll, the carotenoids, and the cyto- 

 chromes. An assignment of the various absorbancy changes associated 

 with these compounds has been made by Clayton (6). 



The purpose of the present communication is to report on the effect 

 of DPIPH2 upon the absorption changes observed with the R. rubrum 

 chromatophore fraction. This leuco dye, DPIPH2, has been shown to 

 be rapidly photooxidized by chromatophores oiR. rubrum m a reaction 

 which appears to be coupled to the photo reduction of components con- 

 tained within the chromatophore. It was of interest, therefore, to ex- 

 amine the effect of DPIPH2 upon the absorption changes in order to 

 see if some correlation can be made between the photooxidation of 

 DPIPH2 and the observed absorbancy changes induced by light. 



Fig. 1 presents the absorption spectrum of /?. rubrum chromato- 

 phores. Fig. 2 presents the absorbancy changes observed when such 

 chromatophores are illuminated. Considering the system with chroma- 

 tophores only, the absorption changes previously noted by others (6, 

 7,9) are shown in the present case also. There are some differences 

 between the difference spectrum for chromatophores shown in Fig, 2 

 and similar spectra reported by others, particularly in the region 

 from 250 to 300 rafi. These differences most likely arise from the fact 



1 Contribution No. 109 from the Charles F. Kettering Research Laboratory, 



269 



