298 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



Gyorgy 335 reported that rice bran extract acts synergistically with mixed 

 tocopherols in retarding the oxidation of linoleic acid, and consequently 

 in preserving carotene. 



However, even with added hydroquinone, carotene was found to be less 

 effective as a source of vitamin A when fed in certain oils than when ad- 

 ministered in others. 332 Thus, it was much less active when given in 

 butterfat 336 than when administered in cottonseed oil. Kraybill and 

 Shrewsbury 336 found, after treating butterfat Avith Lloyd's reagent, that 

 ^-carotene was stable at 40°C, although it was only 50% as potent bio- 

 logically as when it was fed in cottonseed oil. These workers 336 suggested 

 that "Lloyd's reagent may have removed a factor which supplemented the 

 vitamin A activity of the carotene." Lathbury and Greenwood 337 re- 

 ported that a much lower biological response was obtained with /3-carotene 

 when it was given in coconut oil with or without hydroquinone than when 

 it was administered in linseed oil. 



Quackenbush, Cox, and Steenbock 338 ' 339 were the first to demonstrate 

 that tocopherol renders the action of /3-carotene possible; these workers 

 concluded that tocopherol functions by virtue of its antioxidant action on 

 carotene in the gastrointestinal tract. On the other hand, Sherman 340 

 expressed the view that tocopherol was concerned with the utilization of 

 carotene rather than with protection from oxidation, although he also 

 showed that a-tocopherol was highly effective in preserving carotene in 

 the presence of highly unsaturated acids. 



Harris, Kaley, and Hickman 341 made further studies of the synergism 

 exerted by the tocopherols on the biopotency of carotene. They reported 

 that 0.5 mg. of natural mixed tocopherols provides an optimum daily dose, 

 as a demonstration of the sparing action of vitamin E on carotene. In 

 another study, these workers 342 reported that the three tocopherols (a-, 

 j8-, and 7-) are equally effective in sparing carotene and vitamin A, al- 

 though they show marked variations as antisterility vitamins. When 



335 R. M. Tomarelli and P. Gyorgy, J. Biol. Che?n., 161, 367-379 (1945). 



336 H. R. Kraybill and C. L. Shrewsbury, /. Nutrition, 11, 103-110 (1936). 



337 K. C. Lathbury and G. N. Greenwood, Biochem. J., 28, 1665-1673 (1934). 



338 F. W. Quackenbush, R. P. Cox, and H. Steenbock, /. Biol. Chem,, 140, civ-cv 

 (1941). 



339 F. W. Quackenbush, R. P. Cox, and H. Steenbock, J. Biol. Chem., 145, 169-177 

 (1942). 



340 W. C. Sherman, Proc. Soc. Exptl. Biol. Med., 47, 199-200 (1941). 



341 P. L. Harris, M. W. Kalev, and K. C. D. Hickman, J. Biol. Chem., 152, 313-320 

 (1944). 



342 K. C. D. Hickman, M. W. Kalev, and P. L. Harris, /. Biol. Chem., 152, 321-328 

 (1944). 



