METABOLISM OF fAROTENOIDS AND VITAMINS A 537 



one-half of that of /S-carotene,"-'^ the value as given by the more exact 

 methods of bioassay'^^* were recorded as 28% of that of jS-caroteneJ'^-^^^ 

 This figure is almost identical with that (26%) obtained for the 7-carotene 

 obtained from the berries of the narrow-leaf firethorn {Pijracantha angusti- 

 JoUa Schneid.)/*® However, when all-^mns-y-carotene was prepared by 

 stereoisomerization^'*''" of pro- 7-carotene, its biopotency was found to be 

 42% of that of /3-carotene, both in the rat^^ and in the chicken J^^ A similar 

 high biopotency (47%) was recorded for all-/mns-7-carotene prepared from 

 tomato paste (see Table 4).^^ The cause of the variations in the provitamin 

 A activity of the all-^rans-7-carotene obtained from the several sources is 

 not certain. 



Crj'ptoxanthin appears to have a biologic activity slightly higher than 

 50% in the rat tests (55%, 57%, 60%),^*^-^^" although it is possible that 

 these figures may be within experimental error of the 50% value. With''^^ 

 suggested that a qualitative difference exists between the chick and the rat 

 in the utilization of ciyptoxanthin as a provitamin A; he actually concluded 

 that this carotenol was more potent as a source of vitamin A in the chick 

 than was |S-carotene. A variation of this nature in the metabolism of a 

 carotenol such as cryptoxanthin might be expected in the chick since, un- 

 like the rat, the fowls are able to store relatively large amounts of the di- 

 hydroxycarotenes such as lutein and zeaxanthin in their fat depots and else- 

 where. However, Johnson, Swick and Baumann^^^ failed to confirm the ob- 

 servation of With. Actually these latter investigators showed that the 

 carotenol was inferior to /3-carotene as a source of vitamin A in the chick, 

 although the vitamin A storage in the liver following the administration 

 of carotenol was only slightly less than that derived from a hke quantity of 

 /3-carotene. Greenberg et alJ^^ reported that all-^rans-crj^ptoxanthin ex- 

 hibited a provitamin A biopotency of only 55% of that of all-^rans-/3-caro- 

 tene in the chick, using growth as the criterion for the evaluation. It 

 would thus appear that cryptoxanthin exhibits a similar biopotency in the 



'« R. Kuhn and H. Brockmann, Klin. Wochschr., 12, 972-973 (1933). 



''^ H. J. Deuel, Jr., C. Hendrick, E. Straub, A. Sandoval, J. H. Pinckard, and L. 

 Zechmeister, Arch. Biochem., 14, 97-103 (1947). 



"" S. M. Greenberg, C. E. Calbert, J. H. Pinckard, H. J. Deuel, Jr., and L. Zech- 

 meister, Arch. Biochem., 24, 31-39 (1949). 



'** H. J. Deuel, Jr., E. R. Meserve, C. H. Johnston, A. Polgd,r, and L. Zechmeister, 

 Arch. Biochem. 7, 447-450 (1945). 



^" H. J. Deuel, Jr., S. M. Greenberg, E. Straub, T. Fukui, A. Chatterjee, and L. 

 Zechmeister, Arch. Biochem., 23, 239-241 (1949). 



"0 S. M. Greenberg, A. Chatterjee, C. E. Calbert, H. J. Deuel, Jr., and L. Zechmeister, 

 Arch. Biochem., 25, 61-65 (1950). 



'" T. K. With, Z. Vilaminforsch., 17, 88-97 (1946). 



