58 



John M. Olson and Robert M. Smillie 



typical in shape for those wavelengths which activate both photo- 

 chemical reaction 1 (R^, the cytochrome -oxidizing reaction) and 

 reaction 2 (R2, the cytochrome -reducing reaction). The steady- 

 state curve for 0.68 pi light is typical for those wavelengths 

 which activate R-j^ only. Completely analogous steady-state ctirves 

 have been obtained with Euglena using 0.70 p. light for B.-^ and 

 0.65 [i light for Rj^ + Rg. Kok and Beinert^) have obtained from 

 Anacystis cells curves of ESR signal intensity (ascribed to pho- 

 tocatalyst P-7OO) vs. actinic light intensity which are very 

 similar to our cytochrome curves. 



Action Sx)ectra ; The relative effectiveness of the various 

 light-absorbing pigments in driving H-^ and/or R2 can be ascer- 

 tained in principle by determining the action spectra for light- 

 driven cytochrcane oxidation and for light-driven cytochrome re- 

 duction. We have derived action spectra frcm families of curves 

 of cytochrcsne oxidation vs. actinic light intensity. In 



EUGLENA: ACTION SPECTRA 



h 



I 



PCMll 



600 



DCMU 

 MINUS control/ \\ 



/ \ 



CONTROL I \ 



h 



750 m^ 



Fig. 3» Action spectra of cytochrome-552 oxidation in 

 arbitrary units of reciprocal intensity compared to the 

 absorption spectrum (l-T) of the -vdiole cell suspension. 



