254 ELECTRON TRANSPORT 



TABLE 4. 



Rates of dark enzymatic reactions of chromatophores . 

 The reaction mixtures (4 ml total volume) contained 

 chromatophores equivalent to 0.1 and 0.165 mgof BChl 

 for R. rubrum and Chromatium respectively, ivith the 

 buffer concentrations listed in Figs. 1 and 7. The ex- 

 perimental system for NADH-DPIP diaphorase also 

 contained 1.5 fimoles of NADH and 0.27 /umoles of 

 DPIP, that for DPIPH2 oxidase contained 0.27 /umoles 

 of DPIPH2 and that for NADH oxidase contained 0.6 

 ju moles of NADH. The diaphorase assay ivas performed 

 under anaerobic conditions at 25°C. 



//molesAr/mg Chlorophyll 

 R. rubrum Chromatium 



CORRELATION OF KNOWN PHOTOREACTIONS IN R. RUBRUM 



It would be well to compare the rates of DPIPH2 photooxidation with 

 other photo re actions which have been reported in the literature. Table 

 5 reports the rates we have observed for both R. rubrum and Chroma- 

 tium. The rates reported are average values, and the fastest photooxi- 

 dation rate observed to date was the fast reaction with NAD present, 

 which amounted to 553 jumoles DPIPH2 oxidized per hour per mg of 

 BChl, This reaction, then, is one of the fastest reactions reported for 

 the photochemical system of the bacteria. In general, Chromatium 

 particles were less active on a chlorophyll basis. The data again 

 show the lack of a coupled slow reaction with either NAD or fumarate. 



The rates for photophosphorylation reported in the literature usually 

 fall between 100-300 /umoles per hour per mgof chlorophyll (16,41,42, 

 43). However, M. Baltscheffsky has reported a photophosphorylation 

 rate of 620 /imoles per hour per mg of chlorophyll (44). The rates of 

 the two reactions, the photooxidation of DPIPH2 and ATP formation 

 under the influence of light, are certainly very similar. Again this lends 

 support to the idea that the photooxidation of DPIPH2 observed is 

 mediated by the central closed electron transfer system contained in 

 R. rubnim chromatophores, and that the same light- activating system 

 is active in both cases. 



The rates of other photooxidation and photo reduction reactions re- 

 ported in the literature fori?. r?^/n7^;;/ chromatophores have been com- 



