540 IX. CAROTENOIDS AND VITAMINS A 



one I.U. of /3-carotene (which by definition weighs 0.6 ug.), and from one 

 I.U. (or U.S.P. unit) of vitamin A which weighs 0.3 Mg.^"''^^" Mattson/^^ 

 in his review of the vitamin A requirements of various species of animals, 

 stated that the minimum daily requirement, to support groAvth and to pre- 

 vent symptoms of deficiency in mammals, is 40 I.U. (24 jig,.) per kg. body 

 weight when given as /3-carotene, or 20 I.U. when administered as vitamin 

 A. Another typical result showing a corresponding relationship between 

 j8-carotene and vitamin A is that reported by Braude et a/.,'^^' which indi- 

 cated that pigs require 100 I.U. of vitamin A per lb. of body weight, while 

 the corresponding requirement in terms of ;S-carotene is 300 I.U. Accord- 

 ing to Gurcay et aL,^°* the vitamin A requirement of turkey poults, to as- 

 sure normal growth, was one-half as great when black-cod liver oil was 

 used as a source of vitamin A, and one-fourth as much when crystalline 

 vitamin A acetate was employed, as when crystalline ^-carotene was 

 used. 



On the other hand, Koehn^^^ reported that ;S-carotene is quantitatively 

 converted to vitamin A in the rat provided that adequate quantities of 

 a-tocopherol are available. Moreover, Burns, Hauge, and Quacken- 

 bush^^ reported that there was no difference in the biologic response of rats 

 to 1.0 jug- of vitamin A and to a similar amount of |S-carotene, respectively, 

 when 1.0 mg. of tocopherol was given per day. How^ever, the possibility 

 exists that the levels of /3-carotene and of vitamin A used in the tests of 

 Koehn,^^^ and possibly also in the experiments of Burns et al.,^^ were high 

 enough to induce a nearly maximal growth response, and hence were in 

 the non-critical area of the groAvth curve. According to Harris,^^^ this 

 would render it difficult to distinguish between real differences in potency. 

 The author is also of the opinion that the dosages are too high for a critical 

 assay, and believes that the second theory best explains the quantitative 

 relationships in the transformation of jS-carotene, and of other carotenoids 

 with provitamin A activity, to vitamin A. It is possible that an in vitro 

 reaction might result in a greater efficiency in the transformation of /3-caro- 

 tene to vitamin A, although Goss and McFarlane^^^ obtained only 30 to 40% 

 of the theoretical yield by oxidation of |S-carotene with osmium tetroxide. 



b. Cis-Trans Isomerization of Carotenoids, and Provitamin A Activity. 

 Although the phenomenon of geometric isomerism has been recognized for 



'6' J. R. Fov and K. Morgareidge, Anal. Chem., 20, 304-307 (1948). 

 '62 p. L. Harris, Ann. Rev. Biochem., 18, 391-434 (1949). 



'6^ F. H. Mattson, Requirements of Animals, in W. H. Sebrell, Jr., and R. S. Harris, 

 The Vitamins, Vol. I, Acad. Press, New York, 1954, pp. 163-170. 

 ■'^^ C. J. Koehn, Arch. Biochem., 17, 337-344 (1948). 

 '65 G. C. L. Goss and W. D. McFarlane, Science, 106, 375 (1947). 



