DIGESTION, ABSORPTIOX, AND DIGESTIBILITY 429 



well as of /^-carotene are present in the livers and eggs of chickens following 

 their administration constitutes an a priori proof for the absorption of these 

 compounds. 



Lycopene, which has the same empirical formula as /3-, a-, and 7-caro- 

 tenes (C40H56), but in which the jS-ionone rings have both been ruptured, is 

 likewise absorbable, as eA'idenced by its presence in human fat,^ human 

 liver,^^ human blood serum,^'- as well as in the milk fat of the cow.^^ There 

 is no evidence as to the ease and speed of absorption of lycopene as compared 

 with /3-carotene, since no experimental data are available on this point, and 

 lycopene is not a pro^'itamin A. The latter fact precludes a comparison 

 of absorption rates based upon the speed of accumulation of \dtamin A in the 

 liver. 



Several of the oxycarotenoids are absorbable, as determined by indirect 

 methods. Cryptoxanthin, C40H55OH, which is a provitamin A, is not 

 absorbed as such by the rat,®'* and chicken,^^ but is converted to vitamin A 

 in the wall of the intestine. However, the presence of cr^-ptoxanthin in 

 cow's butter^* and in the blood serum^^ of cattle proves that this species can 

 absorb it unchanged. In the case of hens, the presence of lutein in egg 

 yolk has been demonstrated;" this indicates that the carotenol is not entirely 

 broken down to vitamin A in the gut wall by this species, and that some 

 unchanged portion must escape the intestinal barrier, to gain entrance into 

 the body. 



There is like^^^se considerable evidence for the absorption of the two iso- 

 meric dihydroxycarotenols, lutein and zeaxanthin. Neither of these acts 

 as a provitamin A. However, the presence of lutein has been reported in 

 human fat,*"-*^ in the livers, obtained postmortem,^^ from presumably 

 normal men, as well as from patients who had died from a variety of ill- 

 nesses.^^ The dietary origin is proved by the fact that it was found in the 

 human skin after large amounts of wdnter (Hubbard) squash {Cucurbita 

 maxima) had been consumed.''" ■'^^ Zechmeister and Tuzson"- reported a 



«« L. Zechmeister and P. Tuzson, Z. physiol. Chem., 231, 259-264 (1935). 



61 L. Zechmeister and P. Tuzson, Z. physiol. Chem., 234, 241-2-44 (1935). 



62 E. V. Ddniel and G. J. Scheff, Proc. Soc. Exptl. Biol. Med., 33, 26-30 (1935). 



63 A. Gillam and I. M. Heilbron, Biochem. J., 29, 834-836 (1935). 



6* S. M. Patel, J. W. :\Iehl, and H. J. Deuel, Jr., Arch. Biochem., 30, 103-109 (1951). 

 6* J. Ganguly and H. J. Deuel, Jr., Unpublished experiments, 1952. 



66 A. E. Gillam and M. S. ElRidi, Biochem. J., 29, 2465-2468 (1935). 



67 A. E. Gillam and I. M. Heilbron, Biochem. J., 29, 1064-1067 (1935). 



68 L. Zechmeister and T. Tuzson, Z. physiol. Chem., 225, 189-195 (1934); 226, 

 255-257 (1934); 234, 235-240 (1935). 



69 H. Willstaedt and T. Lindquist, Z. physiol. Chem., 24O, 10-18 (1936). 

 '" H. Suginome and K. Ueno, Bull. Chem. Soc. Japan, 6, 221-228 (1931). 

 " M. Ansai, Japanese J. Med. Sci., V. Pathology, 1, 175-190 (1931). 



■2 L. Zechmeister and P. Tuzson, Bull. soc. chim. biol., 17, 1110-1118 (1935). 



