CAROTENOIDS 



Me Me Me 



? Brown Chromoprotein 



The difference in physical properties between astaxanthin and astacin 

 are noted below. 



Absorption 

 m.p. spectra maximum 



Carbon disulphide 

 Astaxanthin . . 215-216° ' « 502 my.. ^'''^ 



240-243'^^' 



Astacin 



500 my.. 5 a 



It must be remembered that astaxanthin, once considered a specific 

 •crustacean carotenoid, has recently been detected in plants {see p. 135) 

 and insects (see p. 221). 



Formation 



It is now generally accepted that synthesis of carotenoids de novo 

 by arthropods (or, for that matter, by any animal) does not occur. The 

 little evidence that is available, however, dates back to 1926 and 1927. 

 Lwoff -^ °' ^ ^ showed that the eye pigment {see p. 167) of Idya was derived 

 from the egg pigment, and by raising this animal on carotenoid-free 

 regimes (marine mussels, washed rabbit red cells, Escherichia coli, etc.), 

 he showed that the pigment was for the most part of alimentary origin ; 

 he suspected that the caroteno-proteins were endogenous. According 

 to Fox,* Lwoff has now abandoned this view. The crab Carcinus 

 maenas stores carotenoids in its hepatopancreas and excretes them in its 

 faeces ; on a carotenoid-free diet the hepatopancreas and the faeces lose 

 their carotenoids. ^ ». "^ » 



Brown "^ investigated quantitatively the carotenoid variations in 

 the shrimp, Palaemonetes vulgaris^ when it was maintained on various 

 backgrounds. Those kept on a white background lost most of their 

 pigmentation whilst those on a brown or black background maintained 

 or even increased their carotenoid concentration. Fox* has criticized 

 this work and points out that these results cannot be taken as indicat- 

 ing carotenoid synthesis by the shrimp, for many uncontrolled factors 



172 



