544 NIACIN 



The exact form in which nicotinic acid and its amide are bound in plant 

 tissue is not known. Several groups of investigators'-^--'^ found evidence of 

 an alkali-labile precursor of nicotinic acid in wheat bran. The substance 

 was purified to some extent and found to have nicotinic acid activity for 

 the dog.-^ The exact nature of this substance has never been determined, 

 although the latter workers suggested that it might be a simple ester of 

 nicotinic acid. Chaudhuri and Kodicek-^ obtained evidence of a precursor 

 of nicotinic acid in wheat, barley, rice brans and corn.-^ This precursor is 

 inactive for L. arabinosus and differs from Krehl and Strong's material in 

 that it is not active in animals (rats) unless first hydrolyzed. This material 

 has been purified to some extent, and the suggestion has been made that 

 it may be nicotinic acid with a residual substance attached through the 

 carboxyl group .^^ 



These findings may offer an explanation for the work of Chitre and 

 Desai.^" These investigators developed an animal method for estimating 

 the availability of nicotinic acid in foodstuffs. Using this method, which 

 has some inaccuracies and limitations, they found that the availability of 

 nicotinic acid was only 60 % in rice, 81 % in wheat, 76 % in gram, 70 % in 

 tur, and 92 % in yeast. They also showed that in viiro digestion, using en- 

 zymes to simulate in vivo digestion, effected a release of nicotinic acid to a 

 degree consistent with the in vivo availability experiments. Cheldelin and 

 Williams-^ also noted the apparently incomplete release of nicotinic acid 

 from cereals when enzyme digestion was compared to acid digestion. 



C. SITES OF OCCURRENCE 



The distribution of nicotinic acid, and its derivatives, is not uniform 

 within a given food product. In most foods of vegetable origin nicotinic 

 acid tends to be concentrated in the outer coverings. For example, wheat 

 bran contained 330 y per gram, and patent flour 12 y per gram, whereas 

 the whole wheat from which it was derived assayed 70 y per gram;^* pol- 

 ished rice contained 0.9 y per gram, brown rice 6.9 y per gram, and rice 

 polishings 96.6 y per gram.^^ Likewise, much of the nicotinic acid in corn 

 is found in the bran and, like wheat, in the germ.^' Apple peelings contain 



23 V. H. Cheldelin and R. R. Williams, Ind. Eng. Chem. Anal. Ed. 14, 671 (1942). 



24 J. S. Andrews, H. M. Boyd, and W. A. Gortner, Ind. Eng. Chem. Anal. Ed. 14, 663 

 (1942). 



25 W. A. Krehl and F. M. Strong, /. Biol. Chem. 156, 1 (1944). 



26 W. A. Krehl, C. A. Elvehjem, and F. M. Strong, /. Biol. Chem. 156, 13 (1944). 



27 D. K. Chaudhuri and E. Kodicek, Biochem. J. 47, xxxiv (1950). 



28 E. Kodicek, Biochem. J. 48, viii (1951). 



29 D. K. Chaudhuri and E. Kodicek, Nature 165, 1022 (1950). 



3« R. G. Chitre and D. B. Desai, Ind. J. Med. Research 3, 471, 479 (1949). 



31 P. R. Burkholder, I. McVeigh, and D. Moyer, Yale J. Biol. Med. 16, 659 (1944). 



