PHOTOOXIDATION AND PHO TOR EDUCTION REACTIONS 239 



Fig. 2. Influenceof/i. ra6r?/;» chromatophore concen- 

 tration upon the initial fast photooxidation of DPIPH2. 

 Experimental conditions as for Fig. 1. 



tion, but the extent of the reaction is also directly proportional to the 

 chromatophore concentration, supporting the idea that the photooxida- 

 tion of the DPIPH2 observed in the fast reaction is coupled to the 

 photoreduction of components contained within the chromatophore. The 

 stoichiometry of the reaction, as shown below, is also consistent with 

 this hypothesis. 



The data presented in Fig, 1 are traces made of the actual record- 

 ing and show the noise inherent in the system. In subsequent figures 

 a smooth curve has been drawn over the original tracing, so that the 

 noise is not apparent. 



Another electron donor which reacts in a similar manner in this 

 system is N,N,N',N'-tetramethyl-/)-phenylenediamine, abbreviated 

 TMPD, whose response is shown in Fig. 3. It resembles DPIPH2 in 

 all respects, including the initial fast reaction and the saturation in 

 the absence of an added oxidant. It differs only in that it appears to 

 react faster than does DPIPH2. This compound is an excellent donor of 

 electrons, and has been shown to react with chloranil (26), and with 

 cytochrome c contained in mammalian mitochondrial systems (27), 



The ability of/?, nibrum chromatophores tophotoxidize the reduced 

 forms of methylene blue and cytochrome c was reported earlier (4), 

 The kinetics of such oxidations obtained under tlie present conditions 

 are shown in Fig, 4, For these experiments the methylene blue was 

 reduced enzymatically by succinate in the presence of the chromato- 

 phores prior to illumination, and fumarate was then added to poise 



