PHOTOOXIDATION AND PHO TOR EDUCTION REACTIONS 253 



g 0.0 

 i -0.5 



TEMPERATURE "C 

 FUMARATE ADDED NAD ADDED 



Fig. 14. Heat stability of DPIPH2 photooxidation reactions 

 with R. nthrion chromatophores. The experimental condi- 

 tions outlined for Fig. 1 were employed with 0.20 mgof BChl 

 present. The chromatophores were heated at the indicated 

 temperature for 5 minutes before addition to the reaction 

 system and commencement of the illumination period. The 

 photooxidation reactions were run at the usual temperatures. 

 The rates for the slow reactions were multiplied by 10 in 

 order to place them on the same scale as the fast reactions. 



tional part of the entire electron transport system for the observed 

 fast reaction. The stability of the fast reaction reported here agrees 

 with the previously reported stability of the aerobic photooxidation of 

 DPIPH2 as reported by Lindstrom (6). 



The rates of various related dark enzymatic reactions for chroma- 

 tophores of R. nibnim and Chromatium are given in Table 4. These 

 are the various dark enzymatic reactions which might be expected to 

 influence the photoreactions under investigation. The R. rubrum 

 chromatophores have a very potent NADH-DPIP diaphorase, which is 

 most likely the enzyme which has been studied in some detail by Horio 

 and Kamen (36). R. nibnim has very weak DPIPH2 oxidase activity 

 and a moderate NADH oxidase activity. Chromatium also has a potent 

 NADH-DPIP diaphorase activity, and has a very active DPIPH2 oxidase 

 activity. This is surprising because this organism lives under anaerobic 

 conditions and does not practice a respiration involving oxygen, where 

 a terminal oxidase would be expected to function. 



