207 



Daniel I. Arnon 



least two pigment systems, each of which carries out separate 

 partial reactions essential to the over-all process (see review, 

 62). Recent work with isolated chloroplasts, in which the par- 

 tial reactions of photosynthesis have been experimentally separ- 

 ated, has contributed biochemical evidence in support of the 

 idea of at least two collaborative photoreactions. Photoproduc- 

 tion of oxygen requires the participation of chlorophyll b but 

 light absorption by this pigment is not essential for the photo- 

 reduction of ferredoxin and the ensuing TPN reduction and photo- 

 phosphorylation. These seem to be associated with the chloro- 

 phyll a pigment system. Ferredoxin is assigned a key role in the 

 energy conversion process in chloroplasts as an electron carrier 

 in both cyclic and noncyclic photophosphorylation. A hypothesis 

 is presented which attributes to molecular oxygen gas the func- 

 tion of a redox "buffer" in cyclic photophosphorylation by 

 chloroplasts. 



REFERENCES 



(1 

 (2 

 (3 



(4 



(5 

 (6 



(7 

 (8 



(9 

 (10 



(11 

 (12 



(13 



Arnon, D. I., Allen, M. B. and Whatley, F. R., Nature Jj4, 



394 (1954)- 

 Arnon, D. I., Whatley, F. R. and Allen, M. B., J. Am. Chem. 



Soc. J6, 632^1 (195^) . 

 Paper presented by D. I. Arnon before the Am. Chem. Soc. in 



New York, Sept. 11, 1957, and published by Arnon, D. I., 



Whatley, F. R. and Allen, M. B., Science _12I, 33O5 (i9!?8X 

 Arnon, D. I., paper presented at the Cell Symposium, Amer. 



Assoc. Adv. Sci., Berkeley Meeting (195^); Science 122 . 



9 (1955). 

 Arnon, D. I., Nature J^, 10 (1959). 

 Arnon, D. I., in Light and Life , ed. by McElroy, W. D. and 



Glass, B., 489 (Johns Hopkins Press, Baltimore, 1961). 

 Losada, M., Whatley, F. R. and Arnon, D. I., Nature 190 , 



606 (1961). 

 Arnon, D. I., Losada, M. , Whatley, F. R. , Tsujimoto, H. Y. , 



Hall, D. 0. and Horton, A. A., Proc. Nat. Acad. Sci. 



(U.S.) 4l, 1314 (1961). 

 Tagawa, K. and Arnon, D. I., Nature 19^, 537 (1962). 

 Whatley, F. R. 



Acad. Sci 

 Tagawa, K. , 



Acad. Sci 

 Tagawa, K. , 



Acad. Sci 

 Tagawa, K, 



Tagawa, K. , and Arnon, D. I., Proc. Nat, 



1247 (1963) 



(U.S.) 49, 266 (1963) 

 Tsujimoto, H. Y. and Arnon, D. 



(U.S.) 49, 567 (1963). 

 Tsujimoto, H. Y. and Arnon, D. 



(U.S.) ^, 544 (1963). 

 Tsujimoto, H. Y. and Arnon, D. 



, Proc . Na t . 

 , Proc. Nat. 

 , Nature 199, 



