533 



John A. Bergeron 



has a well defined 680 mn component (Fig. 6). If this were due 

 to chlorophyll it should be exaggerated with U36 mn excitation 



u 



UJ 



cr 

 o 



3 



Fig. 6. The fluorescence of acetone extracted Anacystis . 



and depressed with 578 m\i excitation. Since the two curves are 

 almost identical we conclude that most of the 68O mn emission of 

 the extracted organisms is not due to chlorophyll and that, there- 

 fore, the phycocyanin is in a state which resembles the effect of 

 aggregation on a mixture of monomeric and dimeric phycocyanin. 

 If the fluorescence of phycocyanin in vivo is similar to the 

 emission observed in this case for the residue then the enhanced 

 fluorescence at 68O mn is explained. Figure 7 illustrates the 

 fluorescence of Anacystis at room temperature for equal quanta 

 absorbed at ^36 m\i and 578 m|i for a very dilute suspension. We 

 have superimposed the fluorescence of the extracted organisms, 

 monomeric phycocyanin and dimeric phycocyanin. Depending upon 

 the curve selected to represent the contribution of phycocyanin 

 to the fluorescence excited by 57^ mi-i light, it could be concluded 

 that energy absorbed by phycocyanin is between 1 to U times as 

 effective in exciting chlorophyll as light absorbed at U36 m\i. 

 If we consider screening by carotenoids then light absorbed by 

 phycocyanin probably is 50 to 100^ as effective in exciting 

 chlorophyll fluorescence as light absorbed directly by chloro- 

 phyll. 



ACTION OF PHYCOCYANIN IN PHOTOSYNTHESIS 



The essence of the preceding paragraphs is that the enhanced 

 activity of phycocyanin in photosynthetic oxygen evolution can 



