3 FUNCTION IN THE ANIMAL ORGANISM 15 



his collaborators^^. These workers have shown that in general the greatest 

 biological activity is exhibited by those pro-vitamins which possess a ^raws- 

 configuration throughout*. The following table** demonstrates these rela- 

 tionships. 



TABLE 2 



RELATIONSHIP BETWEEN VITAMIN A ACTIVITY AND STERIC 

 CONFIGURATION OF SOME CAROTENOIDS* 



)?-Carotene, /ya>2S-configuration throughout 10 0% 



Neo-/3-carotene U (probably 1 cis-linkage) 3 8 % 



Neo-^-carotene B (probably 2 c/s-linkages) 53% 



a-Carotene, /yaws-configuration throughout 53% 



Neo-a-carotene U (probably 1 cis-linkage) 1 3 % 



Neo-a-carotene B (probably 2 cfs-linkages) 1 ^ % 



y-Carotene, ira^s-configuration throughout * * 2 8 % 



Pro-y-carotene (probably 5 ji^-linkages) 4 4 % 



The potency of pure ^-carotene is used as a standard (100 %). 

 ** According to R. Kuhn and H. Brockmann, Klin. Wochschr. 12 (1933) 972, 

 y-carotene has the same vitamin A potency as a-carotene, instead of half the potency as 

 shown here. 



The fact that a-carotene mono-epoxide, ^-carotene mono-epoxide, /3-carotene 

 di-epoxide and luteochrome all exhibit vitamin A activity although (with the 

 exception of jS-carotene mono-epoxide) they do not possess an unsubstituted 

 j3-ionone ring, deserves special mention"*". It may be deduced that these com- 

 pounds are partly de-oxygenated in the organism of the rat. 



TABLE 3 



COMPARISON OF THE BIOLOGICAL ACTIVITY OF SOME 

 CAROTENOID EPOXIDES*^ 



P. Karrer and E. Jucker, Helv. Chim. Acta 28 (1945) 429, 430. 



y-Carotene isolated from mimulus blossoms (p. 162) is an exception to this rule. 

 ** Taken without alteration from L. Zechmeister and co-workers, Arch. Biochem, 

 7 (^945) 247. 

 References p. ly-ig. 



