DIGESTION, ETC. OF CAROTENOIDS IN THE G.I. TRACT 293 



of xanthophyll present is of prime importance in that it may enhance 

 the deposition of vitamin A in the tissues under one condition and inhibit 

 its deposition under other conditions. 



g'. The Effect of Pteroylglutamic Acid: Low values for serum carotene 

 have been shown to occur in sprue. Darby and co-workers 289 observed 

 that this condition is gradually improved following therapy with pteroyl- 

 glutamic acid. The fact that a typical flat curve obtains after with- 

 drawal of the treatment during a relapse is taken as evidence of the in- 

 fluence of pteroylglutamic acid on the absorption of fat-soluble substances. 



b. The Absorption of a- and 7-Carotenes. Although no quantitative 

 results are available on the rate of absorption of a- or 7-carotenes, there 

 are considerable data to prove that their absorption is in the same range 

 as is that of /3-carotene. Thus, a-carotene has been shown to be effective 

 as a provitamin A to the extent of about 50% of the activity of /3-carotene. 290 

 Since only one-half of the a-carotene molecule is capable of transformation 

 to vitamin A while, from a theoretical standpoint, all of /3-carotene can be 

 transformed to vitamin A, a 50% biopotency of the a-isomer would indi- 

 cate an absorption identical with that of the /3-variety. The biological 

 value of 7-carotene, which was first found 291 to be approximately 26% 

 and later 42% of that of /3-carotene, 292 would likewise justify the conclu- 

 sion that the 7-isomer is as well absorbed as is /3-carotene. One can make 

 a similar statement in the case of pro-7-carotene, which is a naturally 

 occurring poly-a's variety. 292,293 The biopotency of this compound was 

 only slightly less than 50% of that of /3-carotene. Since only one-half 

 of the 7- or of the pro-7-carotene can yield vitamin A, a conversion to 

 vitamin A which equals 50% of that of /3-carotene must be indicative of an 

 absorption equal to that of /3-carotene. 



Another proof which helps establish the absorption of a-carotene is the 

 demonstration of its presence in animal tissues. Although data are not 

 available on animals which store carotene as such, minimal amounts of 

 a- and /3-carotenes have been demonstrated in the liver of rats, as well as 

 in the liver and eggs of chickens, following its administration. 294 



289 W. J. Darby, M. K. Kaser, and E. Jones, J. Nutrition, S3, 243-250 (1947). 



290 H. J. Deuel, Jr., E. Sumner, C. Johnston, A. Polgar, and L. Zechmeister, Arch. 

 Biochem., 6, 157-161 (1945). 



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

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



292 L. Zechmeister, J. H. Pinckard, S. M. Greenberg, E. Straub, T. Fukui, and H. J. 

 Deuel, Jr., Arch. Biochem., 23, 242-245 (1949). 



293 H. J. Deuel, Jr., C. Johnston, E. Sumner, A. Polgar, W. A. Schroeder, and L. 

 Zechmeister, Arch. Biochem., 5, 365-371 (1944). 



294 J. Ganguly, J. W. Mehl, and H. J. Deuel, Jr., /. Nutrition, 50, 59-72 (1953). 



