328 ELECTRON TRANSPORT 



Cell-free extracts were prepared by exposure of intact cells to 

 sonic oscillation or by passage through a French press. The rate of 

 oxygen uptake in the dark decreased to approximately 5 per cent of the 

 level observed in the intact cells prior to rupture. Addition of the 

 supernatant fluid and various cofactors, including mammalian cyto- 

 chrome c, cytochrome c? (isolated from /?. vanuieIii),D'P'N, FMN, and 

 FAD, did not increase the rate of oxygen uptake. In contrast to this, 

 oxygen uptake by cell-free extracts in the light was equal to or greater 

 than that observed in the intact cells (Table 2). 



TABLE 2. 



Oxygen uptake by intact cells and separated components of R. vannielii 



Fraction Cell Free Intact 



I II III IV Extract Cells 



chl./prot.l 12 16.8 36 15 17 — 



O2 uptake^ 



Dark 2.5 0.5 3.0 57 



Light 12.0 6.4 1.8 2.0 21.0 60 



1 chl./prot. = moles of bacteriochlorophyll x lO^/mg. protein. 



2 O2 uptake = m/imoles 02/min. in the presence of 0.001 AI Na succinate. 



Utilizing procedures previously described (3) a variety of fractions 

 were derived from intact cells. The degree of separation and enrich- 

 ment has been described elsewhere (3) and is illustrated in Table 2. 

 Using these preparations, oxygen uptake was measured both in light 

 and darkness. As can be seen in Table 2, oxygen uptake in the dark was 

 carried out only by the fractions containing the least pigment. Oxygen 

 uptake in the dark was not observed with the most highly pigmented 

 fractions. The total rate of oxygen uptake in the dark by the various 

 fractions was equivalent to that observed in the original cell-free 

 extract. It thus appears that separation of oxygen uptake in the dark 

 from light-induced oxygen uptake was achieved, since a high rate of 

 oxygen uptake by the highly pigmented fraction occurred only when the 

 light was turned on. 



Oxidation of Cytochrome by Oxygen or Light. 



Illumination of intact cells under anaerobic conditions resulted in 

 oxidation of the cytochromes. The light-induced cytochrome changes 

 also occurred under aerobic conditions (Table 3) (4). Difference 

 spectra (anaerobic vs. aerobic) in the light were quite similar to 

 those obtained in the dark (Fig. 1). 



