482 



Atusi Takamiya, Hirosi Obata and Eijiro Yakushiji 



Photoconversion of CP 668 to CP 743 



Since the most prominent feature of this chlorophyll protein is its sensi- 

 tivity towards light, experiments were carried out concerning the above- 

 mentioned photoconversion of the dark form, CP 668, to the illuminated form, 

 CP 743 . The reaction was followed by measuring the main absorption changes 

 at 565 m^, 668 mfx and 743 m/i. It was confirmed by the preliminary experi- 

 ments that there was a definite correlation between these photo-induced in- 

 creases and decreases in absorbancy. Fig. 4 shows the time course of the 

 photoconversion. 



First, it was confirmed that the presence of air in the reaction mixture 

 is a necessary condition for the photoconversion of CP 668. After removal of 

 molecular oxygen from the solution, the chlorophyll protein was quite stable 

 towards illumination. On introduction of oxygen (air) to the evacuated system, 

 the capacity for the photochemical change was immediately recovered, the 

 same spectral changes being readily observed on subsequent illumination (i.e., 

 decrease of 668 m/n peak, accompanied by the appearance of peaks at 743 m/i 

 and 565 m^). 



Oxidizing agents other than oxygen were then tested in this respect. 

 Potassium ferricyanide at a concentration of 5 x 10" 3 M was found to replace 

 molecular oxygen. The rate of photoconversion in this case, however, was 

 rather slower than the rate under the light-aerobic condition. Also with ferri- 

 cyanide there was no reaction in the dark. The reaction in the presence of 

 mammalian cytochrome c is shown in Fig. 5. As will be seen in the figure, 

 the light (670 mjn, monochromatic illumination) induced the conversion of 

 CP 668 to CP 743. The rise of the peak at 550 mju is a result of simultaneous 

 reduction of the cytochrome added (similar result was observed with algal 

 cytochrome 553)^"^). Also in this case, there was no formation of CP 743 in 

 the dark. 



2, 6-Dichlorophenol indophenol (DPIP) also was effective in inducing the 

 photoconversion. The time course of the reaction is shown in Fig. 6. The 

 absorption increase at 565 my in this case, however, was not clearly detected 

 owing to the absorption due to the dye added. There was no change in absorption 

 in the dark. 



Reversibility of Photoconversion 



In view of the expected role of the substance in some oxidation-reduction 

 reactions, the reversal of the above-described change of the chlorophyll pro- 

 tein was tested. Light or dark incubation of the illuminated form of the chloro- 

 phyll protein in a pure nitrogen atmosphere did not result in any absorption 

 increase at 668 m^ or decrease at 743 m|x. Considering the circumstance that 

 the presence of an oxidizing reagent made a requirement in the photoconversion, 

 the effects of reducing substances were tested in reversing the change. Among 

 various reducing agents tested, including sodium hydrosulfite, ascorbate, phenyl 



