62 



John M. Olson and Robert M. Smillie 



EFFECT OF CI-CCP ON CYTOCHROME 

 OXIDATION IN EUGLENA 

 [X = 0.70/1, 1 = 11x10-* EINSTEIN cm-2 sec"'] 



X 



.01 





^ 



^ 



.02 



-.03 



DIFFERENCE SPECTRUM 

 LIGHT-DARK 



5x10"' M CI-CCP 



_L 



J_ 



_L 



520 540 560 



WAVELENGTH IN m/i 



580 



Fig. 6 



EUGLENA CHLOROPIAST FRAGMENTS 



Cytochrome b^ Reduction ; When washed chloroplast fragments 

 are prepared from Euglena cells in late log phase, most of the 

 cytochrome -5 52 is lost. When such fragments are suspended in 

 .025 M Tris, pH 7.8 with 10-3 M MgCl2, strong light causes a 

 gradual reduction of cytochrcsne bg which remains bound to the 

 fragments (Fig. 7). If the light is turned off after the reduc- 

 tion is complete, the reoxidation in the dark is extremely slow. 

 If, however, the light is kept on, and the intensity dropped a 

 factor of 10, a light-induced oxidation of the cytochrome occurs 

 after an initial lag of about 20 sec (see upper left insert in 

 Fig. 7). The observation of a light-induced reduction or a 

 light-induced oxidation of cytochrome bg depending upon light in- 

 tensity and the redox state of the cytochrome suggested that both 

 R2 and R, were still functioning. The absence of significant ox- 

 idation tor reduction) of cytochrome bg in the absence of light 

 indicated that this cytochrome cannot be merely a component of an 

 electron transfer system which "short-circuits" a single photo- 

 chemical reaction. 



