540 NIACIN 



of niacin.^" Although the assay values thus give the true niacin content of 

 a foodstuff, they do not therefore necessarily reflect the effectiveness of a 

 foodstuff in preventing pellagra or blacktongue. Indeed, the low values for 

 niacin first found in eggs and milk by this procedure^^ and confirmed by 

 improved chemical methods,^' as contrasted with the known value of these 

 foods in preventing pellagra, were among the first findings pointing to the 

 importance of factors other than niacin in the etiology of pellagra. 



For special purposes, assay methods with different specificities may be 

 of value. A strain of Leuconostoc mesenteroides responds to nicotinic acid, 

 but not to nicotinamide, and has been used for estimation of the former in 

 the presence of the latter.^^- ^- Following appropriate hydrolysis, total nia- 

 cin is obtained. By use of the yeast, Torula cremoris, together Avith a variety 

 of hydro lytic procedures, one may estimate either (1) total niacin, (2) 

 niacin plus trigonelline, or (3) niacin plus trigonelline plus N'-methylnico- 

 tinamide.^^ Some organisms, e.g., Pasteurella suiseptica, utilize nicotinamide 

 but not nicotinic acid;^^ assay of the former in the presence of the latter 

 should thus be possible. None of these procedures has been widely used. 



VIII. Standardization of Activity 



J. M. HUNDLEY 



Both nicotinic acid and nicotinamide are readily available from commer- 

 cial sources in quite pure form. There is little need for reference standards 

 for most purposes. The purity of commercial products can be checked 

 readily by melting point and other tests; they are readily recrystallized if 

 necessary. However, a U.S. P. reference standard of pure crystalline nico- 

 tinic acid is available for those who wish to use it.^ Commercial nicotinic 

 acid, U.S.P. grade,2 must be at least 99.5% C6H5NO2. When dried at 105° 

 for 1 hour it must lose no more than 1 % in weight. When ignited there 

 must be no more than 0.1 % residue. It must have no more than 200 p.p.m. 

 of chloride, 200 p.p.m. of sulfate, and 20 p.p.m. of heavy metals. Nico- 

 tinamide (U.S.P. )^ must be at least 98.5 % C6H6N2O and must lose no more 

 than 0.5 % of its weight after drying over H2SO4 for 4 hours. On ignition 

 there must be no more than 0.1 % of residue, and it must contain no more 

 than 30 p.p.m. of heavy metals. 



60 B. E. Volcani and E. E. Snell, Proc. Soc. Exptl. Biol. Med. 67, 511 (1948). 



" W. J. Dann and P. Handler, /. Biol. Chem. 140, 201 (1941). 



62 B. C. Johnson, J. Biol. Chem. 159, 227 (1945). 



" S. Berkman and S. A. Koser, /. Bacteriol 41, 38 (1941). 



^ U. S. Pharmacopeia Reference Standards, 46 Park Ave., New York 16, N. Y. 



2 U. S. Pharmacopeia, 14th revision, p. 379 (1950). 



