ABSORPTION SPECTRA OF THE PHYCOBILINS 



065 



The only availal)le data on the absorption spectra of the isolated (^. e., 

 protein-free) chromophores are those of Lemberg (1930). He gave the 

 following wave lengths for the maxima of the absorption bands: 



Compound 



Medium 



Wave length 



598 m/i 

 606 mju 



498 niM 



Cyanobilin (from Porphyra tenera) 



Erythrobilin (from Porphyra tenera) 



HCl (cone.) 

 Acid CHCI3 

 HCl (cone.) 



Combination of the pigments with protein shifts the bands toward the 

 red; l)ut the amoimt of this shift is not adequately described by compari- 

 son of the above-cjuoted figures with the positions of the absorption maxima 

 of aqueous exti'acts from algae, because the data on free pigments refer to 

 strongly acid solutions, while those on chromoproteids relate to neutral or 

 only weakly acid solutions. The main absorption maximum of the phyco- 

 cyanin-protein complex lies at 615 m^u in the pH range between 3.5 and 

 7, but is displaced, in concentrated hydrochloric acid, by as much as 41 

 ran toward the red (to 656 m/x). Comparing this strongly acid solution of 

 the chromoproteid with an equally strongly acid solution of the chromo- 

 phore, we find a "red shift" by as much as 58 m^u; comparison with a neu- 

 tral chromoproteid solution would indicate a shift of only 17 m/x. 



Similar figures were given more recently by Wassink (1948) for cyano- 

 bilin from blue-green Oscillatoria (Xmax. = 620 m^i for the chromoproteid, 

 610 mn for the solution of the cyanobilin in chloroform, and 600 mju for its 

 solution in HCl) . 



Extinction curves of aqueous chromoproteid colloids were given by 

 Svedberg and Lewis (1928), Svedberg and Katsurai (1929), Svedberg and 

 Eriksson (1932), and French and co-workers (1948,1951). 



Figure 21.39 shows the extinction curves of the phycoerythrins from 

 five different algae. Three maxima (566, 540 and 498 mix) are always 

 present, but with variable relative intensities, pointing to the existence of 

 three different forms of the pigment (perhaps the same chromophore linked 

 to different proteins). Van Norman et al. (1948) found only two absorp- 

 tion peaks (550 and 495 m/x) in aqueous extract from Iridaea. It also has 

 several bands in the ultraviolet. 



Similar observations were made with phycocyanin. In phycocyanin 

 from a Rhodophycea (e. g., Ceramium rubrum. and Porphyra tenera), Sved- 

 berg and Katsurai (1929) found two bands in the visible, at about 615 and 

 550m)u and ultraviolet bands at 355, 271 and 240 m/x. In the phycocyanin 

 from a Cyanophycea (e. g., Aphanizomenon flos aquae) they found only one 

 visible band, at 615 mju, and ultraviolet bands at 368 and 277 mix. 



