338 VITAMIN REQUIREMENTS 



tocladia pringsheimii (35), Venturia inacqualis (63), Plilyctorhiza vari- 

 abilis (227), and individual isolates of Trichophyton equinum (79) 

 and Glomerella ci?igulata (270). Deficiencies may be complete or par- 

 tial. 



The known function of nicotinic acid is as a constituent of the re- 

 spiratory coenzymes diphosphopyridine nucleotide and triphospho- 

 pyridine nucleotide (257). Diphosphopyridine nucleotide has been 

 isolated from Fusarium tricothecioides (87). 



The biosynthesis of nicotinic acid by mutants of Neurospora crassa 

 has been intensively investigated, with important results. These stud- 

 ies are reviewed by Bonner and Yanofsky (20), and a suggested scheme 

 is shown in Figure 4. Evidence for this pathway comes primarily from 

 the ability of compounds to replace nicotinic acid in the nutrition of 



r^N 



CH 2 -CH— COOH 

 NH 2 



Tryptophan 



CO — CH 2 — CH— COOH 



NH, 



NH— CH=0 



Formylkynurenine 



CO — CH o— CH— COOH 



I 



NH 2 

 NHo 



Kynurenine 

 COOH 



NH, 



3-Hydroxyanthranilic 

 acid 



/^\.CO— CH 2 — CH— COOH 

 NH 2 



OH 



NH, 



3-Hydroxykynurenine 



,COOH 



^xT^COOH 



*N 



Quinolinic acid 



^^COOH 



Nicotinic acid 



Figure 4. The probable pathway of conversion of tryptophan to nicotinic acid in 

 Neurospora crassa. Modified from Greenberg (88), bv permission of Academic 

 Press, Inc. 



