238 



ELECTRON TRANSPORT 



MINUTES 



Fig. 1, Photooxidation of DPIPH2 in the absence and 

 presence of added oxidants. The basic reaction system 

 contained 33 mM Tris buffer, 66 flM DPIPH2 (reduced 

 with ascorbic acid until a faint blue color remained) 

 andR. nibrum chromatophores equal to the concentra- 

 tion of 0.22 mg BChl in a final volume of 8.0 ml (except 

 for the case where no DPIPH2 was present, in which 

 experiment 0.48 mg BChl was present). When fumarate 

 was present the pH was 8.0 and the final concentration 

 of fumarate was 0.75 raM. For the experiment with 

 NAD, the pH employed was 8.5 and the system also 

 contained 0.5 mM DPN, 1.3 mgof lactic dehydrogenase, 

 and 3.1 mM sodium pyruvate. Anaerobic conditions 

 were obtained by three evacuations with alternate 

 flushing with argon gas. Experiments were carried out 

 using Thunberg tubes which were modified by joining 

 the main tube through a T-joint with 2 one-cm Pyrex 

 absorption cells. These cells were spaced to fit into 

 the cell holder of a Spectronic 505 recording spectro- 

 photometer which had been modified to allow one arm 

 of the reaction vessel to be illuminated by a tungsten 

 lamp moimtcd outside the housing of the spectrophoto- 

 meter. The light intensity reaching the reaction vessel 

 was 1.05 X 106 ergs per second per square cm. The 

 experiments were run at 30° C for the fumarate sys- 

 tem, and 20°C for the NAD system. For further details 

 concerning the chromatophore preparation procedure 

 and other techniques employed see reference 25. 



