PHYSIOLOGICAL FUNCTION OF BILE PIGMENTS 



571 



function in the synthesis of hemoglobin is still a matter of conjecture; 

 this aspect will be discussed in Chapter XIII. Bilirubin in blood is in 

 itself innocuous even in high concentration. 



The only established function of bile pigment compounds in bio- 

 logical processes is the role of phycoerythrin and phycocyanin {cf. 

 Chapter IV, Section 7.1.) as photosensitizers in the assimilation of 

 carbon dioxide by red and blue algae. The absorption curves of these 

 compounds are complementary to that of chlorophyll a (chlorophyll b 

 is missing in these algae), since they absorb in the green region of the 

 spectrum, just where the absorption of chlorophyll is weak {cf. 

 Fig. 2). 



700 650 600 550 



500 



450 



U 



1.60 ■ 



1.40 • 



1.20 - 



1.00 - 



0.80 



0.60 



0.40 ■ 



0.20 - 



Fig. 2. Absorption curves of chlorophyll a (I), carotenoids (II), phycocyanin (III) 

 and phycoerythrin (IV) (after Boresch, 316). 



This additional absorption of light energy not only enables the 

 algae to grow in weaker light {201^.^21^29), but also permits the 

 Rhodojyhyceae to use more efficiently the green light which is found 

 in the deeper layers of the sea or the Cyanophyceae to use the filtered 

 light under a surface vegetation of green algae. The maximum of 

 assimilation of Rhodophyceae lies in the green, whereas that of green 

 plants and algae is found in the red. 



