X. EFFECTS OF DEFICIENCY 551 



ral populations of fungi other than yeast that require nicotinic acid have 

 not been observed; however, mutant cultures of Neurospora crassa that 

 require it are readily obtained^ All organisms that do not require it pre- 

 formed in the medium appear to synthesize it; many intermediates in the 

 route of this synthesis, which proceeds from tryptophan to niacin through 

 a series of intermediates, were first indicated by use of mutant cultures of 

 A^. crassa.'' 



In all cultures that require a source of nicotinic acid (or its amide) in 

 the medium, a deficiency in supply is reflected in decreased growth of the 

 culture. Concomitant with such decreased growth there is, of course, a de- 

 creased production of the metabolic end products of the particular culture 

 (e.g., lactic acid production by lactic acid bacteria). Microbiological assays 

 for the vitamin depend upon these effects.^ Aside from these over-all effects 

 upon growth, no effects of nicotinic acid deficiency upon specific phases of 

 metabolism of microorganisms have been reported. Because of the role of 

 the nicotinamide-coenzymes in metabolism, one might expect the ability 

 of resting cells to carry out certain dehydrogenation reactions to be im- 

 paired by deficiency of nicotinic acid. Few studies of a sufficiently quantita- 

 tive character to detect such alterations have been made. Hughes, however, 

 reported that in a nicotinic acid-low medium, L. arahinosus synthesized 

 DPN at a considerably higher rate (24 m^u moles per milligram of cells per 

 hour) than was true in the presence of an excess of nicotinic acid (3 m^i 

 moles per milligram per hour).^ 



B. IN MAN AND ANIMALS 



J. M. HUNDLEY 



1. Relation of Biochemical Functions of Nicotinic Acid to 

 Deficiency States 



A dietary deficiency of nicotinic acid produces deficiency states by virtue 

 of the fact that nicotinamide is an essential component of coenzymes I 

 and II. These coenzymes are required for normal metabolism, indeed, for 

 life itself. If the dietary supply of nicotinic acid is insufficient and the 

 organism is unable to synthesize sufficient amounts of the vitamin (see 

 Section VI), normal metabolism becomes impossible, a deficiency state 

 develops, and the organism eventually dies, if the deficiency is sufficiently 

 severe. 



A great mass of precise information is available on the many biochemical 



7 G. W. Beadle, H. K. Mitchell, and J. F. Nye, Proc. Natl. Acad. Sci. U. S. 33, 155 

 (1947). 



« E. E. Snell in Vitamin Methods, Vol. 1, p. 327. Academic Press, New York, 1951. 



8 D. E. Hughes, Biochem. J. 45, xxxvi (1949). 



