PHOTOSYNTHETIC MECHANISM OF PURPLE BACTERIA 



167 



The difference spectrum in anaerobic peptone is similar to (albeit 

 not identical with) the difference of the absorption spectra of oxi- 

 dized and reduced cytochrome c. This indicates that upon illumina- 

 tion a cytochrome becomes more oxidized. Until its identity has been 



+ 20 



+ 15 



+ 10 



+ 5 



Fig. 3. Difference spectrum of Rhodospir ilium ruhrum, left 1 day in water 

 after flushing with hydrogen ("anaerobic water"). Exciting light was a band at 

 540 van with intensity of L2 X 10^ erga/(cm.^ sec). 



established, we shall call this cytochrome "cytochrome 428" after 

 the wavelength of the maximum in its difference spectrum. 



In aerobic distilled water there is a positive maximum (increase 

 in absorption) at 432 m^u. This is not caused by reduction of cyto- 

 chrome 428 or of Rhodospirillum cytochrome c (3), since the band is 

 too broad and occurs at another wavelength. In the infrared, there is a 



