OXIDATION OF CYTOCHROMES 



175 



peak characteristic of cytochrome difference spectra, reduced minus 

 oxidized* The direction of the change shows that the oxidized form of 

 some cytochrome or combination of cytochromes has a higher con- 

 centration when the bacteria are irradiated than when the bacteria 

 are in the dark. In this respect Chromatium is similar to Rhodospiril- 

 lum rubrum (1,2). However, in the case of Chromatium this dif- 

 ference spectrum does not indicate whether more than one cyto- 

 chrome is involved. 



Dark 



Steody State 

 Level 



Light on 



428-440 mi 



Increasing 

 Optical 

 Density 



Fig. 1. Typical anaerobic light effect observed at wavelengths between 420 

 and 430 niyu. In the above record the change in optical density at 428 m^i 

 minus the change at 440 m^ is shown. 



The kinetics of this anaerobic light effect answer in part the ciues- 

 tion of the number of cytochromes involved. The first and second 

 phases of the anaerobic light effect shown in Fig. 1 at 428 m/x were 

 also recorded at several other wa^'elengths. The spectrum of the 

 first phase is given by curve B in Fig. 2 ; the spectrum of the second 

 phase is given by curve C. The positions of the peaks are fisted in 

 Table I. The diphasic character of the anaerobic light effect suggests 

 that a chain of intermediates is involved in the photosj^nthetic trans- 

 fer of oxidizing equivalents to substrates. Furthermore, the dis- 

 tinct differences between the spectra of the first and second phases 

 indicate that more than one cytochrome is involved. For example, 

 the presence of the .560-m/i shoulder in the spectrum of the second 

 phase demonstrates that a 6-type cytochrome is involved in the 

 second phase in addition to a c-type cytochrome (553-m/i peak) in- 

 volved in both phases. 



Experiments performed with a recording spectrophotometer re- 

 vealed additional reactions of the Chromatium cytochromes in the 



