64 



John M. Olson and Rotert M, Smillie 



The action spectrum of the light-induced reduction of cyto- 

 chrone b^ in chloroplast fragments is compared to the action 

 spectrtmi of cytochrome -5 52 oxidation in whole cells poisoned with 

 DCMU in Figure 8. The former spectrum corresponds to the action 

 spectrum of R^* and is further evidence that chlorophyll a is 

 effective in Rp. The difference between the normalized spectra 

 for Rt and Rg indicates again that a far-red pigment analogous to 

 P-700 is active in R^, but not in R2. 



Effect of 1,10 Phenanthroline ; This inhibitor (10"3 m) de- 

 creased the steady-state level of cytochrome b^ reduction during 

 illumination to about 10-20 per cent of the total change observed 

 in the absence of inhibitor. In addition, a rapid reoxidation of 

 the cytochrome b^ took place immediately when the light was turn- 

 ed off. Therefore, no light-induced oxidation of cytochrome bg 

 at low intensity could be observed in the presence of 1,10 phen- 

 anthroline. It appeared that the cytochrome bg was now part of a 

 "short circuit" of R2. 



Interaction of Cytochrcme-^^^ : When purified cytochrCTie-552 

 (ca. 10"^ M) frcm Euglena is added to washed chloroplast frag- 

 ments (ca. 10"^ M chlorophyll), illumination causes the oxidation 

 (or reduction) of the added cytochrome -5 52. High intensity illum- 

 ination causes the oxidation of cytochrome -5 52. VThen the light 

 is turned off, a rapid reduction occurs in the dark with a half 

 time of ca. 6 sec. (The light-induced reduction of cytochrome bg 

 which is concurrent with the oxidation of cytochrome-552 is about 

 1/3 the change observed in the absence of added cytochrome-552.) 

 Very low intensity illumination causes a relatively slow oxida- 

 tion of cytochrome-552, but the final extent of oxidation is con- 

 siderably greater than that observed with high intensity. Fur- 

 thermore, no reduction is observed upon cessation of the light. 

 A light-induced reduction of cytochrome-552 can be demonstrated 

 with high intensity illumination after partial oxidation with low 

 intensity light. 



-k 

 Addition of 5 x 10 M 1,10 phenanthroline to the reaction mix- 

 ture slows down the reduction of cytochrome-552. The light-in- 

 duced oxidation at high intensity is at least doubled and the sub- 

 sequent reduction in the dark is slowed to about l/lOth the rate 

 in the absence of inhibitor. 



SUMMARY AND CONCLUSIONS 



1) There is not necessarily a one-to-one correspondence be- 

 tween a given light-absorbing pigment (e.g. chlorophyll a) and a 



