36 MYTILOXANTHIN 339 



felted, copper-red needles which melt at 198-200°. (Kofler block). On treating 

 a chloroform solution of the pigment with antimony trichloride, a stable blue 

 colouration is produced. 



Solvent: Absorption maxima: 



Carbon disulphide 517 479 447 m/i 



Chloroform 495 460 428 m^ 



Petrol 484 452 425 m// 



34. SALMON ACID 



The pigments responsible for the red colouration of the flesh of salmon 

 [Salmo salar) have been the subject of a number of investigations with partly 

 contradictory results. In 1885, Krukenberg and Wagner^* estabhshed the 

 presence of three carotenoids, namely xanthophyll, carotene and an unknown 

 pigment. In 1933, the latter was obtained in a crystalline state by von Euler, 

 Hellstrom and Malmberg^® and termed salmon acid. Salmon acid was later 

 studied by Emmerie, van Eekelen, Josephi and Wolff^^. 



The chemical nature of salmon acid is still unknown. According to von 

 Euler and co-workers^^, salmon acid is readily soluble in acetic acid and can 

 be precipitated from the solution with alkali. It forms blue-black crystals and 

 shows a single broad absorption maximum at 485 m/i in pyridine solution. 

 A very weak subsidiary maximum at 525 m^ is also observed. Emmerie and 

 co-workers, on the other hand, report that the pigment exhibits an absorption 

 band near 500 m/< in pyridine solution. In the partition test salmon acid is 

 found entirely in the 90 % methanol layer, 



35. asterin acid 



During an investigation of the carotenoids of the back skin of Asterias rubens 

 and of the eggs of Coregonus albula^^, von Euler and co-workers^^ discovered a 

 previously unknown polyene pigment which they termed asterin acid. The 

 compound possesses properties similar to those of astacene (or astaxanthin) . 

 In a later investigation of Asterias rubens, Karrer and Rubel^''*' found that 

 astacene was present. Asterin acid is therefore probably identical with astacene. 



36. MYTILOXANTHIN 



In the course of extensive investigations concerning the part played by 

 carotenoids in the metabolism of Mytilus californianus shells, Scheer^"^ 

 established the presence of zeaxanthin and of another new pigment, mytilo- 

 xanthin. The latter occurs as such in sea shells and appears to play a part in 

 their metabolism. The structure of mytiloxanthin is still unknown. It appears to 

 References p. 341-343. 



