UEQUIHEMEXTtt FOR VITAMIN E 745 



tocopherol exhibits only one-half of the activity of the natural D-(3-to- 

 copherol. 



(5) Comparative Biopotency of a-, f3-, y-, and 8-Tocopherols 



Bacharach,''^^ who reviewed the subject in 1938, concluded that no 

 difference in relative biopotency could be established for the several types 

 of tocopherols. Howe\'er, Mason --^ reported, several years later, that 

 a-, ^-, and 7-tocopherols had relative biopotencies of one, one-half, and one- 

 quarter, respectively. Karrer and co-workers, ^^^ using sjaithetic materials, 

 noted that a-tocopherol (o,7,8-triniethyltocol) had the highest potency of 

 all of the tocols. Joffe and Harris*^^ reported that the M.F.D. (mean 

 fertility dose) of /3-tocopherol was 1.9 mg., and that of 7-tocopherol 9.0 

 mg., as compared with a value of 0.75 mg. for a-tocopherol. This would 

 make the j8-form four-tenths as potent, while 7-tocopherol would be one- 

 twelfth as potent as the a-form. Weisler et aZ.^^^ observed a similar rela- 

 tionship. Gottlieb et al.*^'' reported that the biopotencies of synthetic 

 a-, I3-, and 7-tocopherols and a-tocopheryl acetate were in the ratio 

 100:25:19:100. When the cure of muscle dystrophy in rabbits was the 

 basis for comparison of biopotency, the potency ratios for a, (3, and 7 types 

 of natural tocopherols^^* were 100 : 30 : 20. The natural D-7-tocopherol Avas 

 almost three times as active as the synthetic DL-7-tocopherol in curing 

 dystrophy, and the natural D-/^-tocopherol exhibited about 30% of the 

 activity of D-a-tocopherol.^^^ For a review of the biopotency of various 

 synthetic compounds related to the tocopherols, the reader is referred to 

 The Lipids, Vol. I, pp. 820-827. Harris*'^^ has also given a short review 

 of the relative biologic potency of various tocopherols. For a discussion 

 of the antioxygenic activity of the several types of tocopherols, see The 

 Lipids, Vol. I, pp. 816-819. 



9. The Requirements for Vitamin E 



(1) Normal Requirements of Animals for Vitamin E 



A large number of standards have been set up for \'itamin E, but they 

 are to some extent arbitrary. The International Unit adopted by the 



«■• A. L. Bacharach, Biochem. J., 32, 2017-2023 (1938). 



^"P. Karrer, H. Koenig, B. H. Ringier, and H. Salomon, Helv. Chim. Acta, 22, 1139- 

 1145(1939). 



««L. Weisler, J. G. Baxter, and M. I. Ludwig, ./. Am. Chem. Soc, 67, 1230-1231 

 (1945). 



«'H. Gottlieb, F. W. Quackenbush, and H. Steenbock, J. Nutrition, 25, 433-440 

 (1943). 



«8E. L. Hove and P. L. Harris, J. Nutrition, 33, 95-106 (1947). 



«9 P. L. Harris, Ann. New York Acad. Set., 52, 342-344 (1949). 



