RELATIONSHIP BETWEEN CAROTENES AND VITAMINS A 509 



Euler's work, Moorc'^^-' arrived at an entirely satisfactory explanation for 

 the carotene-vitamin A interrelationship. This investigator found that, 

 although the liver fat of a vitamin-A-depleted rat failed to respond to the 

 antimon}^ trichloride reaction foi- vitamin A, the test was strongly positi\'e 

 after the administration of either vitamin A or carotene. In either case, 

 the product present in the liver was shown to be vitamin A, since it ex- 

 hibited the characteristic absorption band at 328 m^t. Carotene thus as- 

 sumes the role of a precursor of vitamin A or of a provitamin A, since it can 

 be transformed into the active form of this vitamin in the animal body. 



The relationship between the carotenoids and vitamin A is further eluci- 

 dated by the discovery of their structure. /3-Carotene was shown to have 

 an empirical formula of C40H66, while vitamin A has exactly one-half this 

 number of carbons, and has a composition corresponding to the foi-mula, 

 C20H29OH. Carotene contains two j8-ionone rings, while \^itamin A pos- 

 sesses one. Both molecules have conjugated double bonds in the hydro- 

 carbon chains, there being 1 1 such linkages in j8-carotene and 5 in vitamin 

 A. Vitamin A is a primary alcohol, while /3-carotene has no such group. 

 There is now ample evidence that the /3-carotene molecule is made up of 

 two vitamin A molecules, joined together at the site of the terminal alcohol 

 group, which is removed and replaced by an unsaturated linkage. 



There are many excellent sources of specialized information on the carote- 

 noids. The classic monographs in this field are undoubtedly those of 

 L. S. Palmer,-'^ of L. Zechmeister,-^ and of Ledererj^"* and most recently of 

 Karrer and Jucker.-^ A discussion of the most recently developed field in 

 carotenoid chemistry, namely that of the carotenoid epoxides and their 

 furanoid oxides, is given by Karrer.-^ An excellent summary of the role of 

 carotenoids in animal metabolism was published by Zechmeister,^'' and a 

 more recent one by Fox-^^ Wald^^ reviewed the subject of visual purple in 

 its relationship to the carotenoids, while Heilbron, Jones, and Bacharach,^'* 



IS T. Moore, Biochem. J., 23, 803-811 (1929). 



20 T. Moore, Biochem. ./., 2J,, 692-702 (1930). 



21 T. Moore, Biochem. J., 25, 275-286 (1931). 



-- L. S. Palmer, Carotinoids and Related Pigments, Chemieal Catalog Co., New York, 

 1922. 



'^ L. Zechmeister, Carotinoide, Springer, Berlin, 1934. 



2^ E. Lederer, R^cherches siir les Carotenoides des Animcuix inferieurs, et des Crypto- 

 games, Lons-de-Saunier, Paris, 1937. Cited by D. L. Fox, Ann. Rev. Biochem., 16, 454 

 (1947). 



2* P. Karrer and E. Jucker, Carotinoide, Birkhiiuser, Basle, 1948. Translated and 

 revised by E. A. Braude, Elsevier, New York, 1950. 



''^ P. Karrer, Fortschr. Chem. organ. .Waturstoffe, n, 1-19 (1948). 



" L. Zechmeister, Ergeh. Phijsiol., Sf), 117-191 (1937). 



« D. L. Fox, Ann. Rev. Biochem., 16, 443-470 (1947). 



» G. Wald, Vitamins and Hormones, 1, 197-227 (1943). 



'" I. M. Heilbron, W. E. Jones, and .\. I>. Bacharach, Vitamins and Hormones, ?, 

 155-213 (1944). 



