NICOTINIC ACID (NIACIN) 



acid and nicotinamide. H. Grossowicz and E. Sherstinsky ^^ used 

 " Proteus HX 19 ". Dorfman et al.^'^ used Shigella dysenteriae, and 

 Fraser et al. ^^ and Isbell et al. ^^ used Shigella paradysenteriae. Although 

 these methods have the advantage of requiring less complex media 

 than the Snell and Wright method, they involve a turbidimetric esti- 

 mation of the amount of growth produced ; this is less convenient 

 and less accurate than a titration of lactic acid. Moreover, one of the 

 organisms, Proteus vulgaris, responds to coenzymes I and II as well as 

 to nicotinamide. 



In fact, the only possible rival to L. arabinosus is Lactobacillus 

 casei (helveticus) used by M. Landy and D. M. Dicken ^* for the assay of 

 six B vitamins with one and the same medium. This contains casein 

 hydrolysate and glucose, vitamins and pyrimidines, and is similar in 

 composition to that used by Snell and Wright, though the proportions 

 of the constituents are different. The growth response is not linear, 

 however, and the method gives inferior results to the L. arabinosus 

 method. 



Leuconostoc mesenteroides was used by B. C. Johnson ^^ in con- 

 junction with L. arabinosus to estimate nicotinic acid, nicotinamide 

 and nicotinuric acid in a mixture of the three ; L. mesenteroides is 

 unaffected by nicotinamide or nicotinuric acid, and the increase in the 

 response following hydrolysis with acid is proportional to the nicotin- 

 amide and nicotinuric acid present. Nicotinuric acid is estimated by 

 measuring the difference in the response of L. arabinosus (the growth 

 of which is stimulated by both nicotinic acid and nicotinamide) before 

 and after hydrolysis, and the amount of nicotinamide present is calcu- 

 lated by subtracting the value so obtained from the previous result. 



A yeast, Torula cremoris, was used by W. L. Williams, ^^ the growth 

 of the organism being measured turbidimetrically. Differential assays 

 of nicotinic acid, trigonelline and N^-methylnicotinamide were carried 

 out with this organism by measuring the response before and after 

 acid and alkaline hydrolysis. 



A modification of the Heatley method of assaying antibiotics ®^ 

 has been tried out for the assay of growth factors, including nicotinic 

 acid.^^ An agar plate was seeded with L. arabinosus and holes were 

 cut in the agar or, alternatively, little porcelain cups were placed on 

 the surface of the agar. Into the holes or the cups, a little of the test 

 solutions and standards were poured, the plates were incubated and 

 the diameters of the zone of " exhibition " (analogous to the zones of 

 inhibition produced by antibiotics) were plotted against the logarithms 

 of the concentrations. Although this gave a straight line, the method 

 suffered from the same disadvantages as the conventional microbio- 

 logical assay together with the added disadvantage that the edges 

 of the zones tended to be diffuse. 



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