LUCILE SMITH 



439 



tion or in the dark with aeration, and the same substrates can be 

 oxidized in the two conditions (13) . The difference spectra of Fig. 

 3 show that ilhnnination resuks in the oxidation of the same cyto- 

 chrome system which is oxidized in the dark with oxygen, and in ad- 

 dition at least one more cytochrome is also oxidized on illumination. 

 The latter cytochrome has a peak in the difference spectrum around 

 420 lUfx, ^\ hich woidd correspond to the cytochrome C2 of the bacteria, 

 which has been isolated from these organisms by Vernon (14, 4) . 

 Isolated cytochrome Co does not interact rapidly with the dark respira- 

 tory chain of the bacteria (8) . 



Further studies were made w4th cell-free extracts of R. riibrum, 

 which can respire in the dark (8) and, as shown by Frenkel (5) , 

 can promote rapid phosphorylation of adenosine diphosphate (ADP) 

 on illumination. Fig. 4 shows that illumination of cell-free extracts 



Rhodospirillum rubrum 

 grown in ligRf 



■anaerobic minus aerobic (dark) 

 •anaerobic dork nninus anaerobic light 



reference = 470n>i 



400 420 440 460 



Wavelength in millimicrons 



Fig. 3. Difference spectra of R. rubrum grown under illumination. The data 

 were obtained with the double-beam instrument at the wavelengths indicated; the 

 reference wavelength is 470 m^. 



