50 



Bessel Kok 



maximum at 700-705 mu. This 700 maximum is quite weak in 

 mutant #8 and subtraction of the excitation spectra measured 

 with the two algae (as done in Fig. 3 for the absorption 

 spectra) yields a distinct band at 698 mu, present in the 

 normal alga only. Obviously C700 sensitizes the emission at 

 730 mu. This might still be compatible with a quenching of 

 F73O if one assumes that C70O transfers energy from sensitiz- 

 ing pigment (Chl. a) to P730, but either can be bypassed or 

 is needed only in a low concentration such as still might be 

 present in the mutant: F700 F730 



hV — » Chl a — ^ C700^— ^ 0730^ (l) 



I r 



In the previous section we have tentatively located C7OO 

 in photosystem I, if scheme (l) were correct, F730 should be 

 sensitized by the same pigment system. To check this, we 

 have measured the excitation spectra for F7OO and F730 in 

 chloroplasts and various types of algae. In each species 

 these spectra proved to be quite similar for the two emis- 

 sions — which is an argument for scheme (l). Hovi/ever, the 

 data failed to indicate a correlation with"photosystem I": 



In Anacystis the excitation of F7OO and F73O revealed the 

 typical ineffectiveness of 68O mu light (1/2 - 1/3 of 63O 

 light) and also lacked the 700 band which is so evident in 

 chloroplasts and green algae. (The red alga TX 27, however, 

 showed a distinct sensitization band at 710 mu.) 



Figure 3 shows the fluorescence emission of the alga TX 27 

 excited either by green light (3^6 + 378 mu) which sensitizes 

 photosystem II (and I) via phycoerythrin or by blue light 

 (^36 mu) which mainly sensitizes photosystem I. 



The multiplication factors required to bring the spectra 

 of Fig. 5 to equal hei^-ht (indicated on the curves) show that 

 green light is much more effective than blue, both at room 

 temperature (4x) and at 77°K (l6x). Although, at 77*K the 

 730 band is predominant in the blue excited emission, it stiLl 

 is induced (9x) more effectively by green light. For the 683 

 and 698 emissions this ratio is ^50 fold. The data of Fig. 3 

 [xn accord with those of Brody and Brody (l)J do not support 

 the simple thesis that "F730" originates from photosystem I. 

 They further show that F7OO as well as F683, even more exclu- 

 sively than F730,are sensitized by green light i.e. by photo- 

 system II. Actually, also the excitation spectra measured 

 with green cells--although more difficult to analyze — favor 

 this conclusion. 



