276 ELECTRON TRANSPORT 



photochemical apparatus (2,3,10,11,12) and the photophosphorylation 

 coupled with the electron transport system. 



The present speech will deal with the photosynthetic and nonphoto- 

 synthetic electron transport systems and related phosphorylation in a 

 facultative photoheterotroph, Rho do spirillum ruhrum. 



PHOTOSYNTHETIC AND NONPHOTOSYNTHETIC RESPIRATION 



Photosynthetic bacteria, whether facultative anaerobes or strict 

 anaerobes, consume molecular oxygen in the presence of substrates 

 (respiration with broad meaning). There is a dramatic effect of illumi- 

 nation on the respiratory activity of the facultative photoheterotrophs. 

 This was first observed by Nakamura (13), who noted that illumination 

 suppressed oxygen consumption with a cell suspension of Rhodo- 

 pseudomonas palustris. Using R. rubrum, Johnston and Brown (14) 

 demonstrated that oxygen is not produced in detectable amounts during 

 the light- inhibited oxygen respiration, providing a strong argument 

 against Nakamura' s postulate that the light inhibition may be due to a 

 light- stimulated production of oxygen. On the other hand, Sistrom, 

 Griffiths, and Stanier (15) have found that cells oiR. rubrum grown 

 aerobically in darkness (dark-grown cells) are largely devoid of the 

 photosynthetic pigments (bacterio chlorophyll and carotenoids) and that 

 respiration of the cells is not influenced by light. 



As expected, cells of R. rubrum grown anaerobically in light 

 (light-grown cells) and suspended in a growth medium consumed 

 oxygen faster in darkness than in light (Fig. 1). However, the ratio 

 of dark-to- light respiration varied from culture to culture, with values 

 as high as 4.5, Optimal pH values were 7.7 for dark (total) respiration, 

 8.0 for light (light- insensitive) respiration, and 7.5 for respiration 

 which could be inhibited by light (light-sensitive) (18). Respiration of 

 the dark-grown cells was not influenced by light and showed optimal 

 pH at 8.0 either in light or in darkness; the respiration rate oiR. 

 rubrum was much slower than that of the ordinary aerobic bacteria 

 possessing cytochrome oxidases; the Qo2 ^^ 30°C and pH 7 was 15 to 

 20 mm,3/hour/mg. for dark respiration of the light-grown cells and 

 somewhat greater (25-45 mm.3/hour/mg.) for respiration of the 

 dark-grown cells. With light-grown cells, the Q02 for dark respiration 

 and the ratio of dark-to- light respiration declined gradually as the 

 cells were aged or aerated. 



/7-Butanol and ethanol, tested as possible narcotics, inhibited all of 

 the light-sensitive respiration at 0.15 M and 1.2 M, respectively, but 

 had little effect on the light-insensitive respiration (Fig. 2). The effect 

 of narcotics could be easily removed by a simple washing of the cells, 

 Allyl alcohol inhibited both respirations. Ethylene glycol also inhibited 

 the dark respiration to a lesser extent, but the ratio of dark-to-light 



