THE PHYCOBILINS 417 



D. The Phycobilins* 



A water-soluble blue pigment was discovered in blue-green algae by 

 von Eisenbeck in 1836. Seven years later, Kutzing (1843) extracted a 

 similar red pigment from red algae and called it phycoerythrin, suggesting 

 at the same time the name phijcocyanin for von Eisenbeck's blue com- 

 pound. The spectroscopic properties and the (very intense) fluorescence 

 of these pigments were first studied by Schiitt (1888). Molisch (1894, 

 1895) showed that the reactions of the aqueous extracts to heat, alcohol, 

 and salts were those of colloidal protein solutions. The separation of 

 the chromophoric groups from the carrier protein was achieved by 

 Lemberg (1929), who introduced the name "phycobilins" because of 

 the similarity between these chromophores and the bile pigments, e. g. 

 bilirubin. Kutzing (1843) found that phycoerythrin is present also in 

 the blue-green algae; and this was confirmed by Boresch (1921) and 

 Wille (1922). Similarly, the red algae often contain some phycocyanin. 

 It may be fair to say, therefore, that the two pigments usually occur 

 together (similar to the occurrence of the two chlorophylls, or of carotene 

 and the carotenols). According to Kylin (1931), the Florideae, which 

 live below 3-5 meters under the sea, contain only phycoerythrin and are 

 therefore bright red, while those growing nearer to the surface also 

 contain phycocyanin and are therefore brownish, purplish, or violet. 



The relation between phycocyanin and phycoerythrin is similar to 

 that between the two chlorophylls and between carotene and carotenol 

 in that one is, according to its formula, an oxidation product of the other. 

 The ''oxidized" pigment (phycocyanin) occurs in several varieties, 

 distinguished by their shades— green-blue, blue, purple-blue (Molisch 

 1906; Kylin 1910, 1911, 1912, 1931) and reminding one of the different 

 carotenols. The "reduced" pigment (phycoerythrin) appears to be the 

 same in red and blue algae, although Kylin (1912) noticed some variations 

 in fluorescence and later (1931) also in the absorption spectra of phyco- 

 erythrins from different sources. The identification of the different 

 varieties of the phycobilins is complicated by two facts: In the first 

 place, many observations of allegedly different phycocyanins have been 

 probably due to variable admixtures of phycoerythrin; and, in the second 

 place, changes in the extinction curves of the chromoproteids may be 

 due to variations in the nature of the proteins rather than of the 

 chromophores. 



It seems that the occurrence of phycobilins in the plant world is 

 restricted to the two classes of algae mentioned above, the Rhodophyceae 

 and Cyanophyceae; however, similar pigments are found, according to 

 Lemberg, in fishes, and perhaps also in sponges and bacteria. 



* Bibliography, page 435. 



