346 PHOTOMECHANICAL CONSIDERATIONS 



ESR Signal of 

 TMPD Free Rodical 



ESR Signal of R. rubrum 

 Chromataphores in the Light 



Magnetic Field »■ 



Fig. 3. A magnetic field scan of the first derivative ESR signals due to TMPD 

 and R. rubrum chromatophores in the light. The modulation was sufficiently 

 high (4 gauss) to reduce the resolution of the hyperfine lines of the TMPD radi- 

 cal ion so that only the 13 lines which make a larger splitting of 7.4 gauss are 

 evident (10). The oxygen tension was reduced as described in the text. 



luminated R. rubrum chromatophores, a complex relationship was 

 established. Fig. 3 shows a magnetic field scan of the ESR signals in 

 an anaerobic system containing TMPD and chromatophores in the 

 light. The signals due to both TMPD and the chromatophores show a 

 larger steady state value upon illumination. Light of 880 m^, where 

 only the bacteriochlorophyll absorbs, is effective in this reaction. 



Taking advantage of the fact that the chromatophore signal is 2 to 3 

 times as broad as that of the TMPD (9,10), we made preliminary 

 kinetic analyses of the two ESR signals, A span of magnetic field 

 values was chosen where the TMPD first derivative ESR signal 

 changed from one direction to the other, while the light-induced ESR 

 signal from chromatophores had a constant direction. In Fig, 4, each 

 of the curves represents a different magnetic field position arranged 

 so the directions of the two signals first are additive then subtractive. 

 When the light was turned on at an additive point, the total signal was 

 the highest because it combined both signals. In this instance, an 

 increase in ESR signal due to chromatophore is always reflected in 

 the positive direction of the first derivative plot. The curves at the 

 left of the "light-on" series show the increase in TMPD free radical 

 concentration in the positive direction, while the magnetic fields used 

 in those experiments on the right-hand side cause a negative deflection 

 due to increased TMPD radicals. A similar but reverse phenomenon 

 was observed when the light was turned off. In both series of experi- 

 ments, it was observed that the TMPD ESR signal had a faster re- 



