ENERGY TRANSFER IN PHOTOCHEMICAL SYSTEMS 67 



appearance of a long-lived ESR signal. According to this picture, the 

 thermoluminescence referred to earlier would be the result of a deepen- 

 ing of the traps due to drying. 



The electrons and holes in the traps may also be used up by 

 enzymatic processes (processes 5 and 5')- Any reversibility in these 

 enzymatic processes would then lead to a long-lived luminescence 

 which could be classified as a chemiluminescence. It is likely that some 

 of the longer-lived emissions reported by Strehler and co-workers 

 (Strehler, 1951; Strehler and Arnold, 1951) are of this nature and 

 perhaps also the 15-sec emission reported here. The fact that almost 

 three times as much energy is emitted as light in aged chloroplasts as 

 in fresh chloroplasts suggests that these enzymes are easily inactivated 

 and that this enzymatic utilization represents the normal pathway for 

 most of the electrons and holes in the living cell. In this way the light 

 energy could be made available to the photosynthetic mechanism. 



REFERENCES 



Arnold, W., and E. S. Meek. 1956. The polarization of fluorescence and energy 



transfer in grana. Arch. Biochem. Biophys., 60, 82-90. 

 Arnold, W., and H. K. Sherwood. 1957. Are chloroplasts semiconductors? Proc. 



Natl. Acad. Sci. U. S., 43, 105-14. 

 Arthur, W. E., and B. L. Strehler. 1957. Studies on the primary process in 



photosynthesis. I. Photosynthetic luminescence: Multiple reactants. Arch. 



Biochem. Biophys., 70, 507-26. 

 Birks, J. B. 1953. Scintillation Counters. Pergamon Press, London. 

 Borthwick, H. A., S. B. Hendricks, M. W. Parker, E. H. Toole, and V. Toole. 



1952. Reversible photoreaction controlling seed germination. Proc. Natl. 



Acad. Sci. U. S., 38, 662-66. 

 Bowen, E. J. 1951. Resonance transfer of energy between molecules. Symposia 



Soc. Exptl. Biol, No. 5, 152-60. 

 Bowen, E. J., and P. D. Lawley. 1949. Crystal size and fluorescence intensity. 



Nature, 164, 572-73. 

 Bowen, E. J., E. Mikiewicz, and F. Smith. 1949. Resonance transfer of elec- 

 tronic energy in organic crystals. Proc. Phys. Soc. {London), 62, 26-31. 

 Bradley, D. P., and M. Calvin. 1955. The effect of thioctic acid on the quantum 



efficiency of the Hill reaction in intermittent light. Proc. Natl. Acad. Sci. 



U.S., 41,563-11. 

 Cario, G., and J. Franck. 1922. The dissociation of hydrogen molecules by 



means of excited mercury atoms. Z. Physik, 11, 161. 



. 1923. Sensitized fluorescence of gases. Z. Physik, 17, 202-208. 



Commoner, B., J. J. Heise, B. B. Lippincott, R. E. Norberg, J. V. Passoneau, 



