LIGHT ABSORPTION BY PIGMENTS lU VIVO 



1853 



11 ally had the three bands (800, 850, 890 m^) characteristic of live ^iAzor/io- 

 daceae. 



Warming to 50-80° C. shifted the main absorption to 800 m/x; further 

 heating to 100° C. brought it to 770 m/i (in analogy to the shift of the chloro- 

 phyll band in boiled leaves) . 



Wetting with methanol, acetone, pyridine or dioxane causes a gradual 

 transformation of the spectrum into the single-peak spectrum of bacterio- 

 chlorophyll in solution, pyridine being the fastest acting agent. 



500 



JOO 

 wavelength in mid 



Fig. 37C.31. Absorption spectrum of Chromatium (after Duysens 1952). Absorption 

 at 950-570 my. is due to bacteriochlorophyll, that at 430-570 mix mainly to carotenoids. 

 The first region is analyzed into three bands, attributed to the three molecular species, 

 "B 890," "B 850" and "B 800." Outside the infrared peak, the spectra of these species 

 are similar, with a maximum at 590 van. 



Action of acids weakens the 800 and 890 m^t bands, and enhances that 

 at 850 m^i, indicating conversion to bacteriopheophytin, whose "aggre- 

 gated form" has a band at 850 m^. No band shift occurs when acid- 

 treated bacteria are heated — in accordance with the behavior of bacterio- 

 pheophytin in solid films (c/. section 3 above). 



Duysens (1952) gave fig. 37C.31 for the absorption spectrum of Chro- 

 matium and the contribution to it of the several carotenoids and the 

 three bacteriochlorophyll-protein complexes, postulated by Wassink (p. 

 703). The latter have band peaks at 800, 850 and 890 mju, respectively. 

 Only the "890 m/x type" (with absorption peak at 873 m^t) is present in 

 Rhodo spirillum, rubrum. 



Upon heating autolysates from Chromatium, the absorption band at 

 890 m/i disappears; the other two infrared peaks are shifted slightly to- 

 ward shorter waves and enhanced in intensity, thus compensating for the 

 loss of absorption at the longer waves (fig. 37C.32). This change is plau- 



