590 VI. CAROTENOIDS AND KELATED COMPOUNDS 



has been shown to be 3,3'-dihydroxy-4,4'-diketo-|S-carotene,^°^'*°'^ while it 

 derivative, astacene, is a tetraketone. 



HjC CH3 H,C CH, 



C CHj CHj CH, CH: '^q'' 



/\ HhIhHhIhHHhIhHhIhH /'\ 



HzC C'C:c-C;C-c:C'C:C-C:C-C:C-C:C-C:C-C:C-C CH.- 



H\l II II l/H 



c c c c 



Astaxanthin (free form) 



Astaxanthin occurs in the protein complex as an ester with an as yet 

 unknown fatty acid. ^"2, 406,407 j^ j^g^g ^ggj^ suggested by Kuhn and S0ren- 

 sen^22 that, in ovoverdin, the hydroxyl groups of astaxanthin undergo an 

 ionization which permits its linkage to protein through a salt-like bridge. 

 Such a type of linkage accounts for the pronounced difference in color be- 

 tween the free and the combined forms of astaxanthin. The formula sug- 

 gested by Kuhn and S0rensen'*22 for the bound form of astaxanthin in- 

 volves four hydroxyl groups and two additional double bonds, which are 

 conjugated. Astaxanthin is probably identical*^'' with hematoxanthin, 



which has been prepared by Tischer^^' from the red rain-water alga (Ilaema- 

 tococcus pluvialis). 



b. Occurrence. Astaxanthin is widely distributed in the Crustacea. 

 It occurs as a chromoprotein in the brownish black complex in the shell, 

 the red complexes of the hypoderm, and in the blue-green pigment of the 

 eggs of the Norwegian lobster {Astacus gammarus) .^'^^■^'^'^ It is also present 

 in the eggs of the spider crab {Maia fiquinado)^^'^ and of the North American 

 lobster [Hotnarus americanu.s),'^^'^''*-'^ as well as of a niunber of other Ctuh- 

 tacea,^^''^^^ including a lake Cladocera, a copepod, the plankton crustacean 

 (Holopedium gibberum) , the fresh-water shrimp (Gammarvs pulex) , and the 

 tentacled mussel {Lima excavata) .^"^^ In the latter three cases the pigment 

 was in the form of an astacene ester, 



«7 R. Kuhn, J. Stene, and N. A. S0rensen, Ber., 72, 1688-1701 (1939). 



«8 N. A. S0rensen, Kgl. Norske Videnskab. Selskabs Sknfter, 1936, No. 1, 1-14. 



