1872 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



absorption bands). Despite the difference in absorption spectrum, both 

 species have the same fluorescence spectrum, making it hkely that, in Chro- 

 matium as well as in Rhodo spirillum, fluorescence is emitted by one pigment 

 complex only. The main fluorescence peak of Chromatium is located at 

 914 m^, i. e., 11 mju on the long- wave side of that of Rhodospirillum, in agree- 

 ment with the relative positions of the absorption bands (at 873 m^i in 

 Rhodospirillum and 890 mn in Chromatium; the latter band is only indi- 

 cated by a hump on the absorption curve). The fluorescent bacterio- 

 chlorophyll complexes thus must be somewhat different in the two species. 



IZOO 



1.0 



0.5 



1100 



1000 950 900 650 600 Xinmfi t-50 



Fig. 37C.46. Absorption and fluorescence spectra of Rhodospirillum ruhrum (after 

 Duysens 1952). The two spectra are approximately mirror-symmetrical. This suggests 

 that the absorption and fluorescence are due to the same molecule (B 890). 



Upon heating to 100° C, autolysates of Chromatium and Rhodospirillum 

 undergo changes in fluorescence shown in figs. 37C.32 and 33 together 

 with the simultaneous absorption changes. In Chromatium, the "B 890" 

 complex disappears and the "B 850" complex becomes fluorescent — 

 probably because the excitation energy of the latter is not lost any more by 

 transfer to the former. In Rhodospirillum,, both the fluorescence band 

 and the absorption band are shifted only very slightly by heating, but lose 

 much of their intensity. In this case, the destruction of the fluorescent 

 "B 890" (more exactly "B 873") complex seems to be only partial, and the 

 product (perhaps, colloidal bacteriochlorophyll, with an absorption band 

 at 780 m/i) is nonfluorescent. 



The intensity of infrared fluorescence of Chromatium, although it is 

 due to "B 890" only, is nevertheless proportional to total absorption by all 

 three forms of bacteriochlorophyll. For example, the ratio of the fluores- 

 cence yields by illumination at 590 mju and at 800 m^u is the same in Chro- 

 matium and Rhodospirillum, although in the first species most of the ab- 



