FLUORESCENCE OF PIGMENTS tfl VIVO 



1873 



sorption at 800 m/x is due to "B 800." This indicates a better than 80% 

 (perhaps, 100%) efficient transfer of excitation energy from "B 800" to "B 

 890." Fig. 37C.48 shows the action spectra of fluorescence and phototaxis 

 of Chromatium (the latter is assumed by Duysens to represent also the action 

 spectrum of photosynthesis, cf. p. 1188), in the region of predominant carot- 

 enoid absorption. Carotenoids clearly contribute their excitation energy 



WO 



50 



CHROMATIUM 



to 



to 



■51 

 5^ 



g^ 



absorption spectra m 



fl uorescence spectrum * 



•X 



9000 

 U— 



10000 



1200 



MOO 



WOO 



to 



0.5 



Xin rufi 



Fig. 37C.47. Infrared absorption and fluorescence spectra of Chromatium (after 

 Duysens 1952). Except for a slight shift, the fluorescence spectrum is identical with that 

 of Rhodospirillum, indicating that only B 890 fluoresces. 



to both fluorescence and phototaxis, but with only about 35-40% efficiency 

 (compared to that of bacteriochlorophyll in the 590 m^i band). 



A marked difference between the shape of the absorption spectrum and 

 that of the phototaxis action spectrum was noted by Duysens (in agree- 

 ment with Manten, cf. p. 1188) in Rhodospirillum (molischianum, or 

 ruhrum), particularly in older (4-6 days old) cultures. As mentioned on p. 

 1188, Manten attributed this difference to the inactivity of spirilloxanthin. 

 No such difference could be noted by Duysens between the action spectrum 

 of fluorescence and the absorption spectrum ; an efficiency of the order of 

 40% was indicated for sensitized ffiiorescence of "B 890" in spirilloxanthin 

 bands as well as in the bands of other carotenoids (rhodopin). Duysens 

 suggested that two different carotenoid-bacteriochlorophyll complexes 



