32 PHOTOSYNTHESIS 



chlorophylls the position of the bands varies according to the 

 solvent used. 



PHYCOERYTHRIN AND PHYCOCYANIN 



These pigments are associated with the photosynthetic 

 mechanism of the red and the blue-green algae; in the latter 

 phycocyanin predominates. They differ completely from the 

 chlorophylls and the carotenoids in being soluble in dilute 

 aqueous salt solutions, the prosthetic groups being com- 

 bined with proteins of the globulin class. 



Preparation 



Phycoerythrin and phycocyanin are obtained directly 

 when algal cells are broken in dilute aqueous salt solutions. 

 Alternatively a little chloroform may be added to the algae 

 in sea water when the pigments diffuse out, leaving the other 

 plastid pigments in the cell. One of the best sources for pre- 

 paration is the large red alga Porphyra tenera. After extrac- 

 tion the pigments are separated by fractional precipitation 

 with ammonium sulphate and can be prepared in crystalline 

 form. From a purified mixture the two components will 

 crystallize independently, giving simultaneously brilliant 

 red and blue crystals of phycoer}^thrin and phycocyanin 

 respectively. When solutions of the pigments are dialysed 

 free from salt they precipitate and in this form are easily de- 

 natured and undergo a change in colour. In crystalline form 

 and in the presence of io% ammonium sulphate, however, 

 Lemberg has stored preparations unchanged for two years 

 (Lemberg and Legge, 1949). Phycoerythrin and phyco- 

 cyanin are to be regarded as two classes of chromoproteins; 

 differences which depend on the plant source are known to 

 occur and may be due to the protein part rather than to the 

 prosthetic group. 



Chemistry of the prosthetic groups 



The molecular weights of phycoerythrin and phycocyanin 

 were determined with the ultracentrifuge and found to be 

 290,000 and 273,000 respectively. The pigment groups are 

 firmly bound to protein and require strong acid hydrolysis 





