1874 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



are present in these bacteria, one of which is ineffective in phototaxis 

 (and photosynthesis), despite a 40% efficient transfer of energy from the 

 carotenoid in this complex to bacteriochlorophyll, and the capacity of the 

 latter for fluorescence ! 



Duysens found that spirilloxanthin only appeared in old cultures 

 grown in peptone. 



CHROMATIUM 



iog-° 



80 



HO 



O 



X 

 J3 





^ 



/ 



t-0.8 



absorption a 

 spectrum / 



f 

 i 



i 



action spectrum of I action spectrum of B 890- 



•A-A* 



a' 





\'-,^ / absorption spectrum 



•^J^ji^' ofhactePLOchlorophyU 



wave length of incident light in m/j 



O 



L_ 



Q« 



600 



550 



500 



450 



400 



Fig. 37C.48. Absorption and action spectra of Chromatium (strain D) (after Duysens 

 1952). Absorption peak at 590 ni/ix is due to bacteriochlorophyll, absorption between 

 450 and 550 van, mainly to carotenoids. Curves were drawn to coincide at 590 m/u. 

 Light absorbed by carotenoids is equally efficient in exciting phototaxis as well as the 

 fluorescence of bacteriochlorophyll, and about 35-40% as efficient as light absorbed by 

 bacteriochlorophyll. 



The situation is further complicated by a report by Clayton (1951) 

 that, in a different strain of Rhodospinllum ruhrum, spirilloxanthin is active 

 in stimulating phototaxis. (Duysens pointed out that Clayton's experi- 

 ments were made in 10 or 100 times weaker light than those of Manten.) 



With Chlorella, Duysens found the shape of the fluorescence spectrum 

 to be practically the same whether excited by X 480 m/x or 420 m/i, although 

 in the first case, a substantial proportion of the absorbed quanta is taken up 



