CAROTENOIDS AND PHYCOBILINS IN BLUE-GREEN ALGAE 



729 



tract was considerably lower than in the cell spectrum was taken as an indi- 

 cation of extraction losses {cf. Vol. I, page 418, about difficulties of quanti- 

 tative extraction of phycobilins). Therefore, in the construction of the 

 ''combined extract" curve in figure 22.48B, the phycocyanin curve of 

 figure 24.48A was not only shifted, but also increased in height by a factor 

 sufficient to make the phycocyanin peak of this curve coincide with that 

 of the cell curve. 



Emerson and T.ewis pointed out that the agreement between the "cal- 

 culated" absorption curve and the empirical transmission curve (fig. 22.48) 

 is much better than in a corresponding construction for Chlorella. They 

 saw the explanation of this fact in the absence of chloroplasts in Cyano- 

 phyceae, and consequent reduction of scattering. The remaining differ- 



100 



80 



a. 



(T 

 O 



CO 



< 



20 



60—— 



40 



400 440 480 520 560 600 640 680 720 

 WAVE LENGTH, m/i 



Fig. 22.49. Distribution of cell absorption in Chroococcus among pigments (derived 

 from fig. 22.48A and broken curve in fig. 22.48B) (after Emerson and Lewis 1943). 



ences — the enhanced absorption by living cells in the far red, and their 

 weaker absorption in the blue and violet — may reflect significant changes 

 in the true absorption spectrum of the pigment in vivo (cf. part B). The 

 curve for the water extract of all Chroococcus pigments, also shown in figure 

 22.48B, may reflect changes due to separation of the phycobilin-protein 

 from the "chromoplastin" complex as a whole. 



Figure 22.49 shows the apportionment of the absorption by living 

 Cyanophyccae to the three types of pigments. The neat separation of the 

 absorption regions, noted above for the extracts from these cells, appears 

 even clearer in this figure. It shows that blue algae (and perhaps red algae 

 as well) offer particularly favorable conditions for the study of the role of 

 the different pigments in the photosynthetic apparatus. 



The purple bacteria, too, may present favorable conditions for distin- 

 guishing between the absorption by bacteriochlorophyll and by the caro- 

 tenoids, because the absorption maxima of bacteriochlorophyfl are situated 

 in the infrared. Figures 22.25 and 22.27 showed the alternation of the 

 bands of bacteriochlorophyll and of the red bacterial carotenoids in the 

 region below 600 m^u; the strongest bands at about 500 m/x are due to the 



