104 VITAMINS A AND CAROTENES 



given."^"-'^ The same applies to the vitamin A content in the yolk of eggs. 

 Harms'-- made exhaustive researches on the amount of vitamin A in hens' 

 eggs after different ways of feeding. Tn the vegetable cell the carotene is 

 combined with proteins and lipoids.-^' ^" Also in l)lood serimi carotene and 

 vitamin A are combined with proteins. ■"■•*•* In natural compounds vitamin 

 A is very often found as the ester, e.g., in fish liver oils, among others, as 

 palmitic acid ester. ^^"^^ In halibut liver oil up to 95 % occurs as ester,^^ but in 

 egg yolk, 71 to 93 % is not esterified.^*^ The esters of vitamin A are far more 

 resistant to oxidative destruction than the free alcohoP^ and are therefore 

 better for the vitaminization of foodstuff s.'*'' 



In blood about one-fifth of the total vitamin A content is present as 

 ester. This figure rises with large \'itamin A supplies, while the vitamin A 

 alcohol level in the blood remains unchanged. ^^ 



The organs of fresh-water fish and also of sea fish that spawn in fresh 

 water, such as salmon, contain vitamin A 2 which differs in its constitution 

 from vitamin A by possessing one more double bond in the iS-cyclocitral 

 ring. This compovuid was formerly thought to have only minor biological 

 potency.^- Latest experimental results, however, indicate that vitamin Ao 

 is 40% as active as vitamin Ai.*^ )8-Carotene is converted within the or- 

 ganism of fresh-water fish into vitamin A 2.^^ The same applies most prob- 

 ably to other provitamins and carotenoids, whereas in vivo no conversion 



2^ N. K. De, S. Ranganathan, and A. R. Sundararajan, Indian J . Med. Research 34, 

 3 (1946). 



26 C. R. Barnicoat, J. Dairy Research 15, 80 (1947). 



27 B. C. R. Sarkar, /. Dairy Sci. 31, 165 (1948). 



28 F. Harms, Vitamine u. Hormone 2, 36 (1942). 



29 R. Kuhn and H. J. Bielig, Ber. 73, 1080 (1940). 



30 W. Straus, Heh. Chim. Acta 25, 179, 489, 705 (1942) ; 26, 1370 (1943). 



31 L. S. Palmer, J. Biol. Chem. 23, 261 (1915). 



32 W. Kraus, Dissertation, University of Zurich, 19.39. 



33 L. M. Dzialosz3'nski, E. M. Mj^stkowski , and C. P. Stewart, Biuchcm. ./. 39, 63 

 (1945). 



3* L. Reti, Compt. rend. sac. biol. 120, 577 (1935). 



35 S. Hermano, Sci. Papers Inst. Phys. Chem. Research (Tokyo) 32, 44 (1937). 



36 H. M. Kascher and J. G. Baxter, Ind. Eng. Chem. Annl. Ed. 17, 499 (1945). 



37 K. Ritsert, Vitamine v. Hormone 3, 57 (1943). 



38 A. W. Neff, D. B. Parrish, J. S. Hughes, and L. F. Payne, Arch. Biochcni. 21, 315 

 (1949) . 



39 U. P. Basu and S. K. Sen-Gupta, J. Am. Chem. Soc. 70, 413 (1948). 

 ^0 J. G. Ba.xter and C. D. Robeson, ./. Am. Chem. Soc. 64, 2411 (1942). 



^1 H. Popper, F. Steigmann, A. Dul)in, H. Dyriewicz, and F. P. Hesser, Proc. Soc. 



Exptl. Biol. Med. 68, 676 (1948). 

 "2 J. L. Jensen, E. M. Shantz, N. D. Embree, J. 1). Gawley, and 1'. L. Harris, J. 



Biol. Chem. 149,473 (1943). 

 " E. M. Shantz, Scieyice 108, 417 (1948). 

 « R. A. Morton and R. H. Creed, Biochem. J. 33, 318 (19.39). 



