302 ELECTRON TRANSPORT 



(+0.31 V) and the bacteriochlorophyll (+0.4 to +0.52 V) may account 

 for ATP formations coupled with these oxidation- reduction reactions. 

 Although the difference in Eq between FP and cytochrome c? is suf- 

 ficient, it is not known yet whether there is a coupled phosphorylation. 

 Under aerobic conditions, it is certain that RHP is functional as an 

 oxidase. It seems, however, unlikely that RHP is the only factor capable 

 of reacting with molecular oxygen. Other possible oxidizing sites are 

 FP and cytochrome b. The light inhibition of respiration of "young" 

 cells results from the same photochemical act as does photosynthetic 

 ATP formation, confirmatively suggesting that the photochemical act 

 completes the cyclic electron transport system and thus makes oxygen 

 uptake at some of these oxidizable components depressed. The light- 

 stimulated respiration with chromatophores or the "aged" cells is 

 caused by some function of the 410 to 420 m/i component(s), possibly 

 an oxidized product(s) of bacteriochlorophyll, which is absent or not 

 functional in the "young" cells. 



ACKNOWLEDGMENTS 



We would like to express our thanks to Professor M. D. Kamen (Department 

 of Chemistry, School of Science and Engineering, University of California, San 

 Diego), Professor B. Chance (The Johnson Research Foundation for Medical 

 Biophysics, University of Pennsylvania, Philadelphia), and Professor O. Lindberg 

 (WennerGren Institute for Experimental Biology, University of Stockholm, Stock- 

 holm) for their helpful discussions and encouragements and for their kindness in 

 making their facilities available for parts of this investigation. The idea for assays 

 on the action spectra was given by Professor B. Chance to Dr. C. P.S.Taylor (De- 

 partment of Physics, University of British Columbia, Vancouver) and one of us 

 (T.H.). One of the authors (T.H.) is indebted to the Charles F.Kettering Founda- 

 tion, Yellow Springs, Ohio, for all his expenses to participate in this symposium. 



These researches have been in part supported by Grant RG-9246 from the 

 National Institutes of Health, Bethesda 14, Maryland. 



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4. Green, D. E., Electron transport and oxidative phosphorylation. Advan. 

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5. Lehninger.A. L.,and Wadkins,C. D., Oxidative phosphorylation. A;/;/. Rev. 

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