500 IX. CAROTENOIDS AND VITAMINS A 



Although the vitamin A content of whale liver oil (6000 I.U./g.) is re- 

 ported to be considerably lower than that of many fish liver oils, large 

 amounts of kitol are present in whale liver oil, and this is convertible to 

 vitamin A on distillation. Embree and Shantz^^** were the first to discover 

 kitol in whale liver oil, and it has since been found to occur in smaller 

 amounts in fish liver oils,^^"-^'*^ as well as in the liver oil of oxen and sheep.^''"'^*^ 

 According to Barua and Morton^*^ kitol appears to be a di-vitamin A which 

 cannot be depolymerized biologically. Barua and Morton^^^ established 

 the fact that kitol has a chain (or two chains) of four conjugated 

 double bonds instead of the five conjugated double bonds of vitamin A. 

 Rats were found to be unable to convert kitol esters to vitamin A, or to 

 store kitol as such in the liver.*^-^ Kitol also occurs in fin-whale milk. 

 Hickman^*^ believes that kitol is a detoxication product of vitamin A. It 

 should therefore be referred to as a post-vitamin A rather than as a pro- 

 vitamin A. For a further discussion of kitol, the reader is referred to The 

 Lipids, Vol. I, pages 710 to 713. 



Rodahl and Davies^'*^ have made an exhaustive study of the composition 

 of the liver oils of hooded seals {Cystophora cristata), Greenland seals 

 {Phoca groenlandica) , harbor seals (Phoca vitulina), and of an Atlantic 

 gray seal (Halichoerus grypus). Very high levels of vitamin A (up to 

 24,000 I.U./g.) were observed in the liver during the breeding season. On 

 the other hand, a low value of only 388 I.U./g. was noted in four specimens 

 of the liver of Cystophora cristata obtained after the breeding season (in 

 July) . Most of the vitamin A was present in the liver, and only relatively 

 small amounts were found in other tissues. Porpoise liver (Phocaena com- 

 munis) was found to contain approximately 200 jug/g- of carotene, but 

 none was observed in the livers of two embryos. ^^^ 



(c) Carotenoids and Vitamins A in Amphibia. The carotenoids appear 

 to be widely distributed in the Amphibia. Hydroxy carotenoids were re- 

 ported^^^-^^" in the fire-belhed toad {Bombinator igneus). Van Eekelen"^ 

 and Lonnberg^^'' proved the presence of carotenes and of xanthophylls in 



"0 N. D. Embree and E. M. Shantz, J. Am. Chem. Soc, 6''^, 910-913 (1943). 



6" F. B. Cloiigh, H. M. Kascher, C. D. Robeson, and J. G. Baxter, Science, 106, 436 

 (1947). 



"2 K. Hickman, Ann. Rev. Biochem., 12, 353-396 (1943). 



"3 R. K. Barua and R. A. Morton, Biochem. J., 46, 308-317 (1949). 



"4 K. Rodahl and A. W. Davies, Biochem. J., 45, 408-412 (1949). 



"^E. Marcussen, Dansk. Tids. Farm., 17, 73-78 (1943); Chem. Zentr., vol. 114, 

 1943, Part II, 932; Chem. Abst., 38, 5995 (1944). 



^^^ M. van Eekelen, Acta Brevia Neerland. Physiol. Pharmacol. Microbiol., 4, 65-66 

 (1934). 



6« E. Lonnberg, Arkiv Zool, 21 B, No. 3, 1-4 (1929). 



