ANIMAL CAROTENOIDS 



hatched naupHi are entirely pink. * ® This is consistent with the Hbera- 

 tion by denaturation or some similar process of the carotenoid from 

 its protein complex. Ball's ^ ^ work, however, raises another possibility, 

 that the colour is still due to a chromoprotein but one in which the 

 protein-carotenoid linkage has changed from a salt type (ovoverdin) 

 to some other type, for he has succeeded in producing a reddish-pink 

 chromoprotein from the blue material. A solution of the blue pigment 

 in 25 per cent saturated ammonium sulphate was slowly treated with 

 N hydrochloric acid at 0° ; the colour gradually changed from blue to 

 red ; addition of cold disodium hydrogen phosphate solution restored 

 the original colour. If, however, the phosphate was not added but the 

 acid solution brought directly to 50 per cent, saturation with ammonium 

 sulphate the red pigment was precipitated ; it is soluble in water but 

 cannot be reconverted into the blue pigment, the salt linkage having 

 been irreversibly severed. 



When astaxanthin is treated vvith potassium butoxide in the absence 

 of air it turns blue owing to the enolization of the hydroxyl groups 

 foUow^ed by the formation of a potassium salt. 47. & 2, 5 e Qn admitting 

 air this salt is immediately oxidized to astacin, viz. : 



KO He Me Me 



..JL, 

 J 



v^^y\AAA/v\vw"' ■"" o-/>vVv\aa, 



v_/.. 



Me Me Me 



The existence of the blue chromoprotein complex in lobster carapaces 

 is explained in the same way, enolic astaxanthin is bound by ionic 

 forces (salt link) to a protein and is in some way stabilized : 



^ T^Me Me Me M 



Protein 



An explanation of green and brown chromoproteins has not yet 

 been put forw^ard. From the simple considerations of chromophoric 

 groups it might be expected that in the brown chromoprotein only one 

 P-ionone residue is enolized, whereas in the green chromoprotein both 

 are enolized. Such a suggestion is probably an over-simplification 

 and the possibility of stabilized resonance structures must be considered. 



171 



