ANDRE T. JAGENDORF AND GIORGIO FORT I 585 



(low with PMS as cofactor, hut Avere not able to perform a Hill 

 reaction. 



Strong support for this concept can now be found in the experi- 

 ments of Kok and Hoch (17) , in which the cyclic electron transport, 

 forming ATP, was found to occur with spinach chloroplasts in mono- 

 chromatic light at 700 m^u, and above. Previous action spectra had 

 indicated that light of this wavelength, which is absorbed by chloro- 

 phyll a but not by the accessory pigments, is not effective in over-all 

 photosynthesis (7) or in the Hill reaction (6) . Our previous action 

 spectrum for phosphorylation (13) had indicated that 700 m/^ light 

 was not effective for ATP formation with PMS as the cofactor. How- 

 ever, at that time our system was not completely anaerobic. In view 

 of our data with CMU inhibition of PMS in red light, it seems obvious 

 that we must have been measuring an oxygen exchange reaction rather 

 than a true cycle. Thus, if 700 ni/x light does support a true electron 

 transport cycle, it indicates that light received by chorophyll a only, 

 while sufficient to produce XHo and YO in the present scheme, is 

 not sufficient to reduce YO by discharging oxygen. These preliminary 

 considerations suggest that in the future the function of the accessory 

 pigments Avill be found in the steps leading to oxygen evolution, i.e., 

 reaction 3. 



Acknowledgments 



^Ve would like to acknowledge the stimulation due to discussions with Dr. 

 M. Margulies and Dr. J. Kahn in developing some of the ideas in this paper. The 

 experimental work shown here was done with the technical assistance of Miss 

 Marie Smith. 



REFERENCES 



1. .\rnon, D. I., ^'(lture, 184, 10 (1959). 



2. Bishop, N. I., Biochim. Biophys. Acta, 27, 205 (1958). 



3. Brody, S. S.. and Brody, M.. Arch. Biochein. and Biopliys.. 82. 161 (1959). 



4. Brugger, J. E., and Franck, J., Arch. Biochein. and Biophys., 75, 465 (1958). 



5. Chance, B., and Nishimura, M., Proc. Natl. Acad. Sci. U.S., 46, 19 (1960). 



6. Chen, S. L.. Phmt Physiol., 27, 35 (1952). 



7. Emerson, R., Ann. Rev. Plant Physiol., 9, 1 (1958). 



8. Gaffron, H., /. Gen. Physiol., 26, 195 (1942). 



9. Gaffron, H., /. Gen. Physiol., 28, 269 (1945). 



10. Geller, D. M., Thesis, liiv. of Med. Sci., Harvard University (1957). 



1 1. Jagendorf, A. T., and Avron, M., /. Biol. Chem., 231, 277 (1958). 



12. Jagendorf. A. T., and Avron, M., Arch. Biochem. and Biophys.. 80, 246 (1959). 



13. Jagendorf, .\. T., Hendricks, S. B., Avron, M., and Evans, M. B., Plant Physiol., 



33, 72 (19.58). 



14. Jagendorf, A. T., and Afargulies, M., Arch. Biochem. and Biophys. fin press). 



15. Kamen, M. D., this symposium. 



16. Kessler, E., Arch. Biochem. and Biophys., 59, ,527 (195.5). 



