542 



H. Hasegawa and Y. Ogura 



Fig. 7. Oxidation of reduced cytochrome 63 (change in optical density at 557 m/j) 

 by ferricyanide, at 20°C and pH 7-2. 



Fig. 8. Oxidation of reduced cytochrome b^ (change in optical density at 425 m//) 



by thionine (solid lines) and reduction of thionine (broken lines; change in optical 



density at 640 m^O, at lO^C and pH 7-2, 



the addition of thionine, which may be attributed to the insufficiency of the 

 dye added. It is interesting to note that the oxidation of reduced cytochrome 

 Z>2 can be brought about by dyes such as methylene blue or thionine, with 

 oxidation reduction potentials lower than that of cytochrome b^. 



These data seem to suggest that in the enzymic reaction electron transfer 

 to the dye can occur directly from reduced cytochrome b^, but not from the 

 reduced flavin mononucleotide. 



In order to interpret all the findings described above, the following set of 



