CAROTENOIDS 



However, more work is necessary before pigment differences can be 

 put forward as an argument to dissociate the Xanthophyceae from the 

 two other groups. 



Phaeophyceae 



The brown algae comprise the largest class of algae and they vary 

 considerably in size and colour, ^-carotene is present in all species 

 which so far have been studied. The characteristic carotenoid of this 

 species \s fucoxanthin which is as universal as is (3-carotene but occurs 

 in much greater amounts. Fucoxanthin was first isolated in 1914 by 

 Willstatter and Page, ^ ^ ^ but its structure is still in doubt. Heilbron 

 and Phipers favour : 



but Strain ^ ^ •* points out that as this is 5 : 5'-dihydroxycapsorubin, its 

 absorption spectrum should differ little if any from the parent capso- 

 rubin ; this is not so {see Table 4). Neither does the spectrum of 

 fucoxanthin correspond with that of p-carotenone, which contains the 

 same chromophoric system ; ^ ^ ^ other reasons why this structure of 

 fucoxanthin must be rejected are given by Karrer and Jucker. ^ ^ ^ The 

 absorption spectrum of fucoxanthin and its isomer neofucoxanthin are 

 drawn in Fig. 21. 



With little evidence Retrovsky ^ ^ * has suggested the following struc- 

 ture for fucoxanthin ; 



OH 



Me 



Heilbron and Phipers examined a large number of brown algae, 

 choosing those as diverse as possible in their habits. In spite of this 

 diversity the uniformity of pigment distribution was remarkable, 

 fucoxanthin was always the main carotenoid. Lutein (xanthophyll) 

 was detected in small amounts only in the smaller members and was 

 absent from the larger algae. Kylin, ^ ^ * during his first investigations 



132 



