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LIGHT ABSORPTION BY PIGMENTS IN VIVO 



CHAP. 22 



6. Absorption by Carotenoids and Phycobilins in Blue-Green Algae 



Emerson and Lewis (1943) analyzed absorption by the pigments in 

 the blue-green alga Chroococcus, in the manner described on page 722 for 

 Chlorella. Figure 22.48A illustrates the absorption in alcoholic extract 

 containing chlorophyll and the carotenoids, and in aqueous extract con- 

 taining the phycocyanin-protein complex. The separation of the ab- 

 sorption regions is much neater than in green plants: above 650 m/x, 



0.9 



0.8 



0.7 



0.6 



^ 0.5 



if 



g 0.4 

 0.3 



0.2 



0.1 



1 1 1 \ 



— « Alcohol-soluble pigments 

 ■•— Chlorophyll 

 — • Carotenoids 

 —a Phycocyanin 

 X Phycocyanin (Svedberg) 



0.9 



0.8 



I \ \ 



-" Intact cells 

 -« Combined extrocts 

 -« Water extract 



0.6 



0.5 



400 440 480 520 560 600 €40 680 400 440 480 520 560 600 640 680 720 

 WAVE LENGTH, m/x WAVE LENGTH, m/i 



A B 



Fig. 22.48. Analysis of spectrum of Chroococcus (blue alga.) (after Emerson and 

 Lewis 1943). (A) Absorption spectra of extracted pigments in ethanol, and of phyco- 

 cyanin in water. (B) Absorption spectra of intact cells (1.26 mm.' cells/ml., layer 1.4 

 cm. thick), combined extracts (calculated from A by shifting bands as described in text) 

 and of water extract (containing all pigments). Water extract curve has changed shape, 

 indicating alteration of the phycocyanin-protein complex by extraction. 



absorption is due mainly to chlorophyll; between 530 and 640 m^c, to 

 phycocyanin; and between 460 and 510 m/x, to the carotenoids (because 

 of the absence of chlorophyll b) . Below 440 m^, chlorophyll again becomes 

 the main absorber. 



Figure 22.48B is the attempt to reconstruct conditions in the cell. The 

 chlorophyll and carotenoid bands were shifted, as in the treatment of 

 Chlorella, the first ones by 10 m/x in the red, and 6 m/x in the blue and violet, 

 and the second ones by 14 m/x. The phycocyanin band was shifted by 

 6 m/x compared to its position in aqueous extract. In the case of chloro- 

 phyll and the carotenoids, the extraction was assumed to be complete; in 

 that of phycocyanin, the fact that the 620 m/x absorption peak in the ex- 



