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L. N. M. DUYSENS 



decrease at 880 myu and an increase at 790 m^u. The infrared part of the 

 spectrum is probably caused by a change in bacteriochlorophyll (2). 

 Since this type of difference spectrum occurs in the presence of oxygen 

 or oxidizing conditions and disappears under reducing conditions 

 (c/. 4) , the change may be caused by an oxidation of bacterio chloro- 

 phyll. If a small part of the bacteriochlorophyll takes part in this re- 

 action, then the difference spectrum indicates that the 880-mAi 



Fig. 4. Changes in optical density of Rhodospirillum rubrum, at 420 and 430 myu as 

 function of the intensity of the exciting Hght in water flushed with hydrogen. 



peak is shifted to 790 mfj, and the near ultraviolet band to 430 m/i. 

 These shifts may be interpreted as indicating the dehydrogenation of 

 one of the two reduced pyrrole nuclei in bacteriochlorophyll (cf. 5). 



In anaerobic distilled water the negative maximum occurs at 420 

 mfj. (Fig. 3), suggesting the oxidation of Rhodospirillum rubrum 

 cytochrome c, a pigment isolated by Vernon and Kamen (3). The 

 hump at about 430 m/j, suggests the oxidation of cytochrome 428. 



Figure 4 shows that the change at 430 is saturated at a much lower 



