248 



ELECTRON TRANSPORT 



response to NAD and NADH concentrations observed by Horio and 

 Kamen in the caseof NADH- RHP reductase and the NAD photoreduction 

 supported by succinate with R. rubnim chromatophores (36,37). 

 The pH optima of these reactions are shown in Fig. 10. The effect 

 of temperature on the photooxidation of TMPD was examined by fol- 

 lowing the reaction at room temperature and at the temperature of 

 liquid nitrogen. These experiments, shown in Fig. 11, were carried 

 out in collaboration with and through the courtesy of Dr. Britton Chance, 

 The photooxidation of TMPD did not proceed at the temperature of 

 liquid nitrogen, indicating an ordinary chemical reaction was involved 

 in this photooxidation. This distinguishes it from the physical process 

 which results in cytochrome oxidation in Cliromatium (12). 



440 



480 



520 560 600 



WAVELENGTH, m/x 



640 



680 



Fig. 11. Lack of TMPD photooxidation at 77°K. Experi- 

 mental conditions given for Fig. 3 were used, except that 

 the reactions were run aerobically and contained 0.20 

 mg of bacterial chlorophyll. These experiments were 

 performed by Dr. Britton Chance using the spectro- 

 photometer described previously (12). The curve cor- 

 responding to 300° K was taken directly from the re- 

 cording following 30 seconds illumination time with 

 red light. The curve corresponding to 77° K was plotted 

 by taking the difference between the tracing obtained 

 before illumination and following 70-second illumination. 

 The minimum observed at 600 ni^ is characteristic of 

 light absorption changes which occur with chromato- 

 phores alone. 



