148 IV. BILE PIGMENTS 



cyanins, their properties, and their occurrence. The nomenclature was 

 suggested by Svedberg, the letters R and C denoting Rhodophyceae and 

 Cyanophyceae, according to the plant family in which the particular chromo- 

 protein is more commonly found. For a fuller account of their occurrence 

 in algae see references (315,318,1627). 



There may be other phycoerythrins {965,1267 ,1268) and phycocyanins 

 (1627,1973), but their individuality has not been safely established (cf. 315, 

 1670). Phycoerythrin and phycocyanin have also been found in flagellates, 

 dinoflagellates, and in a blue diatom (2428). 



The chromoproteins have the character of plant globulins. They are 

 easily precipitated by ammonium sulfate in crystalline form. At their iso- 

 electric points they are slightly soluble in water. 



7.2. Bile Pigment Chromoproteins in Animals 



From the wings of the common European cabbage butterfly Wieland and 

 collaborators (3072,3076), isolated green and blue chromoproteins. The 

 prosthetic group, which they called pterobilin was obtained crystalline in 

 the form of its dimethyl ester. The analyses gave the formula C35H38O6N4, 

 i.e., that of bilatriene (biliverdin) dimethyl ester. The stability of pterobilin 

 toward concentrated sulfuric acid and the position of the absorption bands 

 of the zinc-biliviolin compound obtained from it show, however, that ptero- 

 bihn is mesobilatriene. 



In a preliminary note. Okay (2073) has reported the occurrence of chromo- 

 proteins similar to phycocyanin and phycoerythrin accompanying carote- 

 noids in the integument of Mantis religiosa and other Orthoptera. Certain 

 glands of the mollusc Aplysia secrete intense violet pigments, from which 

 Lederer (1663, cf. also earlier work of Derrien, 563) isolated aplysioviolin 

 and aplysiorhodin by fractional ammonium sulfate precipitation. Evidently 

 these are bile pigment chromoproteins closely related to phycocyanin and 

 phycoerythrin. Earlier evidence for the presence of such compounds has 

 been reviewed by Lemberg (1670). This was, however, far less convincing 

 and in some instances the blue or green color of carotenoid proteins and the 

 similar color which carotenoids give with concentrated acids has been con- 

 fused with that of bile pigments and bile pigment chromoproteins. The 

 blue pigment of the Mediterranean fish Crenilabrus and related species, 

 first studied by v. Zeynek, is, however, probably related to phycocyanin 

 (Fontaine, 913). 



Meldolesi and collaborators (1898) have isolated myobilin, a chloroform- 

 soluble polypeptide, from the feces of patients with muscular atrophy and 

 destruction of myohemoglobin. It contains mesobilifuscin (anQ;,a:'-dihydroxy- 

 pyrromethene) as its prosthetic group. 



Serum bilirubin is not present free in the blood, but is combined with 

 protein (cf. Chapter XI, 8.3.2.). Two forms of .serum bilirubin have been 

 found, one reacting with diazotized sulfanilic acid in the serum ("direct" 

 bilirubin) and another form which requires certain additions (alcohol, 

 caffeine) for this reaction ("indirect" bilirubin). Both forms contain bili- 

 rubin combined to protein; in the "direct "bilirnl)in the latter is probably 



