534 



John A. Bergeron 



10 

 9 



CO R 



g" 



13 3 



_l 

 u. 2 



-[Mil nil |ll I l|IIM|l III I I II l|lll l|llll |l I l l |l I I I |l II I |l lll | lll I I III l|llll I llll| l l I lll l llll II J. 



Q nillliiiil I III liiiiJi I III 1 1 II lirrrlTi II Inn lijiiTiTiili I III MM liiiil 1 1 I I I iiilll l l l lii n il NT 



620 640 660 680 700 7 20 740 760 780 



Fig. 7. Fluorescence of Anacystis nldulans per quantum 

 absorbed at 578 niM and U36 mi-i compared vith the fluo- 

 rescence of extracted organisms and pure phycocyanin in 

 the monomer and dimer states. 



not "be attributed to action by vay of the bulk of the chlorophyll. 



We have used fluorescence studies at low temperature ^ ^5) 

 (liquid nitrogen) in an attempt to determine whether light ab- 

 sorbed by phycocyanin is preferentially transferred to a species 

 which is not well excited by way of the chlorophyll- -as Figiire 8 

 shows, such a species exists. In Anacystis there are in addition 

 to phycocyanin and chlorophyll two species which are very weakly 

 fluorescent at room temperatxire but appear as major emission 

 bands at liquid nitrogen temperature; one at 7OO m.\i, the other at 

 720 mn. On the basis of location, preferential excitation via 

 chlorcfphyll, and ferricyanide bleaching, we have tentativelv 

 equated the latter species with the P-7OO of Kok and HochV^"), 

 the oriented 705 pigment of Olson and Butler(27*28)^ g^^^ ^q 

 oriented 695 chlorophyll of Sauer and Calvin^ ^9). that is, the 

 energy acceptor or sink for system one of photosynthesis. By 

 analogy, we infer that the 7OO m|i fluorescence which is prefer- 

 entially excited by phycocyanin may be the energy sink for the 

 oxygen evolving system or system two. If this species absorbs on 

 the short wavelength side. of the ordinary chlorophyll a like so- 

 called chlorophyll-670'30) then poor overlap with the bulk of the 

 chlorophyll would account for poor excitation by chlorophyll but 

 excellent excitation via phycocyanin. 



Within the framework of the concept of two spectrally differa± 



