VITAMINS 



337 



occur al the coiners ol llic niouih. The disease calleil ))cllagra is oflcn 

 partly due to iii:>oll;nin defu ieiu y autl carries these same symptoms. 

 It is also common tor patients (o become sensiti\c to light and sufler 

 from blurred vision. These symptoms usually disappear readily when 

 riboflavin is administered. 



Since the substance is essential to so many metabolic reactions, 

 severe and prolonged deficiency leads to serious pathologies, including 

 nerve degeneration, weakness, paralysis, cataracts of the eyes, impaired 

 reproduction, malformations of limbs, and respiratory failure. See 

 Figure 14-2. Obviously, when too extensive, such changes may not be 

 reversed by vitamin therapy. Deficiency of riboflavin alone is rather 

 rare. This fact and a marked lack of specificity in symptoms, compli- 

 cated with other pathological states, make diagnosis of deficiency quite 

 difficult. 



NICOTINAMIDE 

 Chemistry 



This substance has been known since 1867 as an oxidation product 

 of nicotine. Moreover, the disease pellagra was recognized by 1735 

 and postulated to be dietary by 1912. Yet it was not until 1937 that 

 the antipellagra factor was shown to be nicotinamide. 



Almost all organisms synthesize this essential factor, probably by the 

 following route: 



O 



H 



-CHa— CHCOO 



I 

 NH3+ 



tryptophan 



%^ 



C— CHo— CHCOO- 

 NHCHO 



NHv+ 



H OH 



formylkymirenine 



o 



,<:^^— C— CH2— CHCOO- 



^^^Xp^^HCOO 



S^ 



UNH2 



NH3+ 



H2+ 



kynuric acid 



^%.COOH 



/-^COOH 



■N 



^COOH 



^N 



qiiinolinic 

 acid 



nicotinic 

 acid 



kynurenine 



nicotinamide 



(niacin) 



