ABSORPTION SPECTRUM CHANGES 



95 



10. We also noted a serie« of smaller absorption bands in the region 

 550 to 660 ni/i (see Fig. 3), perhaps due to cytochromes as earlier sug- 

 gested by Lundegirdh. 



These results permit the following tentative conclusions: 

 First, there is formed during illumination a compound with an 

 absorption band around 520 mix. In succeeding dark periods, its 

 concentration falls to a level considerably below that of the dark 

 \'alue prior to illumination. This compound can be formed in the dark 

 by thermal chemical reactions as well as by photochemistry, since its 



500 



550 

 WAVELENGTH mu 



600 



TTO 



Fig. 7. Change in optieal density at different wavelengths during ilhimination 

 following heat treatment of Chlorella for 4 minutes at 51 °C. Incident intensity, 

 250 foot-candles in a flow system. Temperature, 25 °C. 



concentration rises again to a higher level in the dark after the initial 

 depression. 



Second, there is also formed another compound with an absorp- 

 tion maximum aromid 648 m/x different from the one having the 520- 

 m/i band chemically. Both of these substances appear to be related to 

 the luminescence process since their concentration and the lumines- 

 cence intensity exhibit similar kinetic behavior and time courses. 



Third, it appears unlikely that the 520-m/z band is due to a chloro- 

 phyll a derivative, since there is no comparable change in the chloro- 

 phyll absorption maximum in the red or blue. Rather, it is suggested 

 that this compound may be a flavin-type free radical which is pro- 



