702 LIGHT ABSORPTION BY PIGMENTS IN VIVO CHAP. 22 



values from 643 to 655 ihm- This seems to indicate a somewhat lesser 

 shift than is found with the a-component; Table 21. VI gives the impres- 

 sion that the same may be true also for the spectra of the two chlorophylls 

 in different solvents in vitro. 



The clearest indication that chlorophyll b retains its identity in live 

 cells is provided by the fluorescence spectrum. According to Tables 24.1 

 and 24.11, the axis of the main fluorescence band of chlorophyll b in vivo 

 lies at about 656 m/x, i. e., only about 5 mn further toward the red than in 

 ether solution (while the axis of the corresponding a band is displaced at 

 least twice as much). This, too, indicates that the absorption band of 

 chlorophyll b in the living cell probably lies at 647-648 mju. 



(c) Red and Infrared Barids of Bacteriochloi'ophyll 



It was stated on page 642 that the bands of bacteriochlorophyll are more 

 susceptible to shifts under the influence of the solvent than are those of 

 chlorophyll. We are therefore not astonished to find that the two bands 

 of bacteriochlorophyll, which are situated in methanol solution at about 

 605 and 770 m/x, respectively (c/. page 017, fig. 21.6), are replaced in live 

 bacteria by bands situated much further in the infrared — at approximately 

 800 and 850-870 m/x in figs. 21.30, 22.26 and 22.36, and at 825 and 875 

 m/x in fig. 22.25. Figures 21.30A and 22.26 {cf. also Table 22. V) indicate 

 a third absorption band close to or beyond 900 m/x, while figure 22.27 shows 

 only one, very strong infrared band beyond 900 m/x. 



Wassink, Katz and Dorrestein (1939) found that the absorption spec- 

 tra of purple bacteria vary from strain to strain, as illustrated by Table 

 22.V and figure 22.36. 



Alcoholic extracts from all organisms listed in Table 22. V showed only 

 one absorption maximum in the red (at 774 m/x, cf. fig. 21.30B) in place of 

 the two maxima of most Athiorhodaceae (a weak one at 800 and a sharp one 

 at 875 m/x), and three of some Athiorhodaceae and all Thiorhodaceae (at 

 approximately 800, 850 and 895 m/x). Analysis of the band shapes made 

 it probable that the spectra of all purple bacteria contain three infrared 

 bands, even if one of them may sometime be concealed by the other two. 

 Similar variations in the spectra of different species and strains of purple 

 bacteria were observed by French (1940). 



The correlation of the "cell bands" with the "solution bands" of bac- 

 teriochlorophyll (fig. 21.6) is not clear. Shall the cell band at 800 m/i be 

 considered as the displaced solution band at 605 m/i, and the cell band at 

 850-870 m/x as the displaced solution band at 770 m/i? This would mean 

 a shift by as much as 4000 cm.-^ for the "orange" and 1500 cm."'^ for the 

 "red" band. The first shift is so large that one is inclined to doubt the 



