476 THE ACCESSORY PIGMENTS CHAP. 17 



Various observations on the extraction of carotenoids from leaves 

 and their oxidation in the process of extraction indicate that the carote- 

 noids are actually associated with lipides and proteins in the living plant 

 cells. In the case of chlorophyll, we have quoted the strong shift of the 

 absorption bands towards the red as a sign of an association with pro- 

 teins. The bands of the carotenoids in the living cells are shifted even 

 more strongly than those of chlorophyll — as shown for instance by the 

 brown color of Pheophyceae {cf. Vol. II, Chapter 22). Whether this shift 

 is due to the interaction with proteins, or with lipides, remains an open 

 question. The above-mentioned behavior of artificial protein-carote- 

 noid complexes speaks against the first alternative; while the change of 

 the spectrum of brown algae caused by heating (cf. Menke 1940) tends 

 to support it, since it indicates a disruption of the complex by denatura- 

 tion of the proteins. 



Carotenoids remain bound to proteins and chlorophyll in colloidal 

 extracts of leaves and algae, described on pages 383 et seq. Figure 

 46 showed the place which Hubert assigned to the carotenoids in the 

 regular pattern of molecules in the chloroplasts. This assignment is 

 hypothetical; however, a close association between chlorophyll and the 

 carotenoids in the living cell is confirmed by the phenomenon of carote- 

 noid-sensitized fluorescence of chlorophyll in vivo, which was observed 

 by Button, Manning, and Duggar (1943), and will be discussed in Vol- 

 ume II, Chapter 24. This association probably is responsible for the 

 carotenoid-sensitized photosynthesis, and may also be a contributing 

 cause of the strong shift of the carotenoid bands in vivo. 



B. The Phycobilins * 



The occurrence of the phycobilins (phycocyanin and phycoerythrin) 

 in the blue-green and red algae was discussed in chapter 15. Here some 

 information will be given as to their as yet incompletely known chemical 

 structure. 



As described in chapter 15, phycocyanin was discovered by von Eisen- 

 beck (1836) and phycoerythrin by Kutzing (1843); the latter gave both 

 pigments their names. Their proteinaceous nature was noticed by 

 von Eisenbeck; its confirmation came from Molisch (1894, 1895) and 

 Kylin (1910). Kylin was probably the first to prepare these chromo- 

 proteids in the crystalline state. Among the more recent investigators 

 of the phycobilins, one may name Kitasato (1925) and particularly 

 Lemberg (1928, 1929, 1930), who succeeded in separating the chromo- 

 phoric group from the carrier protein, and gaining some insight into the 

 nature of the chromophore. Because of their similarity to the bile pig- 

 ments, Lemberg suggested for these chromophores the name phycobilins. 



* Bibliography, page 481. 



