BILE PIGMENT CHROMOPROTEINS 145 



Choletelins can also be obtained as the penultimate step (not the ultimate 

 step as the name suggests) of the Gmelin reaction of bilirubins or biliverdins 

 (802,1713). A bilene-(b)-dione-(a,c) structure (Fig. '^OA) was suggested for 

 them by Lemberg {1679) and Siedel {2do2) obtained such a compound. 

 Other choletelins, e.g., the crystalline choletelin obtained by nitrous acid 

 oxidation of synthetic mesobiliverdin XIII ester with bromine in the pres- 

 ence of methanol, were found, however, to have the bilenetetrol structure 

 (Fig. 2GB) {25rj6). 



The absorption band of the zinc compound of this substance was found 

 at 515 mju; it resembles the zinc compounds of urobilins by its strong green 

 fluorescence. 



Choletelins can be differentiated from bilenes-(b) by the fact that the 

 former are not attacked by ferric chloride, while bilenes-(b) are oxidized to 

 violet biladienes and green bilatriene. In this choletelins behave exactly 

 like tetrahydromesobilenes-(b), but they can be distinguished from the 

 latter by sodium amalgam reduction followed by ferric chloride oxidation. 

 Tetrahydromesobilene is reduced to its chromogen from which it is regen- 

 erated by oxidation. Choletelins, however, yield a chromogen (probably 

 mesobilane) which is now oxidizable beyond the bilene stage to purple 

 biladienes and green bilatrienes. 



7. BILE PIGMENT CHROMOPROTEINS 

 7.1. Chromoproteins of Red and Blue Algae 



The chromatophores of red algae (Florideae and Bangiaceae) and 

 of blue algae (Cyanophyceae) contain red and blue water-soluble 

 pigments in addition to chlorophyll a and carotenoids. The first 

 observer of these strongly fluorescent pigments was apparently N. 

 von Esenbeck {702) in 1836. The names phycoerythrin and phy- 

 cocyan (or phycocyanin) were given by Kutzing (1613). Molisch 

 established their protein nature in 1894 {1971,1972). A good review 

 of the earlier literature has been given by Kylin {1625). 



Phycoerythrins and phycocyanins crystallize remarkably well and are 

 sometimes found as crystals in the cells of the algae. Some of our phyco- 

 erythrin and phycocyanin crystal preparations have kept for twenty years 

 in their mother liquor (about 10% ammonium sulfate solution), on slides 

 under Canada balsam, without losing their shape or optical properties. 



Kylin separated the pigments from each other by fractional precipi- 

 tation with ammonium sulfate and studied many of their properties. 

 Their large scale preparation was described by Lemberg {1670,1673), 

 who developed a spectrophotometric method for the estimation of 

 phycoerythrin and phycocyanin in mixtures. 



