EFFECT OF REDUCED 2,6-DICHLOROPHENOLINDO- 



PHENOL AND N,N,N',N'-TETRAMETHYL-P-PHENYLENE- 



DIAMINE ON THE LIGHT-INDUCED ELECTRON SPIN 



RESONANCE SIGNAL OBSERVED WITH 



RHODOSPIRILL UM RUBRUM^ 



JOHN J. HEISE and LEO P. VERNON 



Charles F. Kettering Research Laboratory, 



Yelloiv Springs, Ohio 



Light shining on photosynthetic bacteria produces effects which 

 may be followed by determining the optical absorption changes of the 

 pigments, the oxidation- reduction reactions that ensue, and (more 

 recently) the electron spin resonance signal (ESR), By correlating 

 optical absorption changes produced by light and by chemical oxida- 

 tion, Duysens (1) and Clayton (2) have suggested that certain of the 

 absorption changes may be due to a photooxidation of bacteriochloro- 

 phyll, Calvin and Androes (3) have also suggested that the light- 

 induced formation of the ESR signals in bacterial chromatophores is 

 due to the oxidation of bacteriochlorophyll. This paper will present 

 evidence that is compatible with the latter suggestion, showing that 

 light-induced free-radical electrons can be influenced by the reducing 

 agents DPIPH2 and TMPD^, which react with illuminated chromato- 

 phores (4,5). 



EXPERIMENTAL PROCEDURES 



R. rubrum (obtained from A, Frenkel) was cultured using a medium 

 containing malate, glutamate, acetate, ammonium chloride, salts, 

 trace elements and vitamins as previously described (6). The cells 

 were grown in 2 or 4 liter bottles at 30-35°C and at a light intensity 

 from incandescent bulbs of ca, 400 ft, -candles. A 4% inoculum was 

 used and the cells harvested in their log phase after 40 hrs. of growth. 



1 Contribution No. 110 from the Charles F, Kettering Research Laboratory. 



2 The abbreviations used in this paper are as follows: AA, ascorbic acid; and 

 TMPD, N,N,N ',N '-tetramethyl-{>-phenylenediamine dihydrochloride. The 

 term "chromatophore" refers to the photosynthetically active particle derived 

 from the whole cell, as explained in reference No. 6. 



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