542 



IX. CAROTENOIDS AND VITAMINS A 



The most complete study of the provitamin A activity of the stereoiso- 

 mers of the carotenoids was made by Zechmeister, in collaboration with 

 the author. Table 4 summarizes the results of these tests. 



With the exception of pro-7-carotene, all czs-isomers of the provitamins 

 A have a lower biopotency than do the naturally occurring all-trans 

 forms. Confirmatory results in support of this statement have been re- 

 ported by Bahl, Sadana, and Ahmad.""* In the case of the 7-carotene set, 

 the biopotency of the poly-czs pro-7-carotene is 50% higher than that of 



Table 4 



The Relative Biopotencies of the Various Stereoisomeric 

 Forms of Provitamins A, as Determined by 



BlOASSAY IN THE RaT AND ChICK 



Table continued 



■"^ A. N. Bahl, J. C. Sadana, and B. Ahmad, /. Sci. Ind. Research {India), 7 B, No. 11, 

 169-171 (1950). 



