356 PHOTOMECHANICAL CONSIDERATIONS 



If unpaired electrons have a direct relation to the primary light 

 conversion act in photosynthesis, these preliminary results can be 

 interpreted as a substantiation of the hypothesis (11,12) that in the 

 green photosynthetic bacteria, chlorophyll- 770 is the terminal energy 

 acceptor and that chlorobium chlorophyll serves as an accessory 

 pigment, although the possibility of a direct participation of chlorobium 

 chlorophyll in some photochemical reaction still cannot be discounted. 



REFERENCES 



1. Commoner, B., Heise, J. J., and Townsend,J., Light-induced paramagnetism 

 in chloroplasts. Proc. Nat. Acad. Sci., 42, 710 (1956), 



2. Commoner, B., Heise, J., Lippincott, B., Norberg, R., Passonneau, J., 

 Biological activity of free radicals. Science, 126, 57 (1957). 



3. Heise, J. J., Electron spin resonance studies of free radicals in photosyn- 

 thetic systems. Dissertation, Washington University, St. Louis, Mo. (1962). 



4. Androes, G. M., Singleton, M. F., and Calvin, M., EPR in chromatophores 

 IromRhodo spirillum rubnau and inquantasomes from spinach chloroplasts. 

 Proc. Nat. Acad. Sci., 48, 1022 (1962). 



5. Heise, J. J., Unpublished results. 



6. Treharne, R. W., Brown, T. E.,and Vernon, L. P., Separation of two light- 

 induced electron spin resonance signals in several algal species. In press. 



7. Calvin, M., and Androes, G. M., Primary quantum conversion in photo- 

 synthesis. Science, 138, 867 (1962). 



8. Ruby, R. H., and Calvin, M., Primary quantum conversion: Electron spin 

 resonance evidence. This volume, p. 335. 



9. Beinert, H., Kok, B.,and Hoch,G., The light-induced electron paramagnetic 

 resonance signal of photocatalyst P700. Biochem. Biophys. Res.Comm., 7, 

 209 (1962). 



10. Olson, J. M., Filmer, D., Radloff, R., Romano, C. A., and Sybesma.C, The 

 protein-chlorophvll- 7 70 complex from green bacteria. This volume, p. 423. 



11. Olson, J. M., and Sybesma, C, Energy transfer and cytochrome oxidation 

 in green bacteria. This volume, p. 413. 



12. Sybesma.C, and Olson, J. M., Transfer of chlorophyll excitation energy in 

 green photosynthetic bacteria. Proc. Nat. Acad. Sci., 49, 248 (1963). 



13. Calvin, M., Some photochemical and photophysical reactions of chlorophyll 

 and its relatives. Light and Life, ed. by W. D, McElroy and B. Glass, Johns 

 Hopkins Press (1961). 



Note added in proof. Recently, light-induced absorbancy changes 

 with a maximum at about 840 m/^ were observed in Cps. ethyliciim 

 (C. Sybesma and W.J. Vredenberg, Biochim. Biophys. Acta, in 

 press), which give evidence for the existence of a reaction center, 

 P 840, directly energy-fed by chlorophyll-770. The ;?,/E3R signal 

 observed in vivo and in the sonic preparation may be due to this 

 reaction center. This suggestion is consistent with the observa- 

 tion that no light-induced ESR signal was evident in a purified 

 watery solution (10) of chlorophyll-770. 



