1854 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



sibly explained by assuming that the "B 890" complex is converted, by 

 heating, into the "B 850" and the "B 800" complexes. 



In Rhodospirillum, heating causes the 873 mix band to drop considerably 

 in intensity, and a new band to arise at 780 m^ (fig. 37.33). Duysens 

 suggested that this new band may indicate the formation of colloidal 

 bacteriochlorophyll. 



Bsgo RHODOSPIRIL L UM RUB RUM 



absorption spectra 

 _, -healed autolysate 

 non heated auloiysate 



Fig. 37C.32. Absorption and fluores- 

 cence spectra of autolysates of Chroma- 

 tiurn (after Duysens 1952). Constant 

 concentration. The long-wave shoulder 

 disappears in heated autolysate, while the 

 absorption at 850 mju, and particularly at 

 800 mju, is enhanced. Fluorescence peak 

 of non-heated autolysate indicates fluo- 

 rescence of B 890, that of heated autolysate, 

 fluorescence of B 850. As long as B 890 is 

 present, B 850 transfers excitation energy 

 to it and does not itself fluoresce. 



Fig. 37C.33. Absorption spectra of 

 autolj^sate of Rhodospirillum rubrum (after 

 Duysens 1952). After heating, the main 

 absorption maximum of the autolysate 

 decreases and new absorption arises at 

 about 780 m/x, indicating that bacterio- 

 chlorophyll had passed into a new state. 

 (Location of the band and absence of 

 fluorescence suggest colloidal state.) 



The 590 m^t peak has a height proportional to the total amount of 

 bacteriochlorophyll, as if all three complexes contributed equally to it — a 

 striking fact, because one would expect complexing to influence also the 

 higher excited electronic levels of the molecule, and not only the lowest one. 



Fig. 37C.31 illustrates the predominant role of carotenoids in the ab- 

 sorption spectrum of Chromatium between 400 and 550 mju. 



Larsen (1954) gave an absorption curve of a suspension of the green 

 sulfur bacteria, of which only the long-wave part had been described 



