E. L. TATUM 



453 



65001 

 10575 



C-83 



^CS?rOj 



a?' 



CHjCH-COOH 

 NH, 



^^ 



n 



^ I T ^ I 



I 



3416 



^^^NH, 



4540 



? 



Y3I88I 



Figure I. Biosynthesis of tryptophan and nicotinic acid in Neurospora. 



Hnic acid (34). Several different mutant strains oi Neurospora are known 

 which require either tryptophan or nicotinic acid for growth. Strain 

 Y-31881 is unable to use tryptophan but can use hydroxyanthranihc 

 acid which is accumulated by strain 4540. Recently strain 4540 has been 

 shown to utilize quinolinic acid (34) which in turn is accumulated by 

 strain 3416 (9,34)- The available evidence indicates that this entire 

 sequence of reactions holds also in the rat (33,34,57)- 



The other known instance of a relationship between an amino acid and 

 a vitamin is somewhat less direct than that just discussed. This is the 

 relationship established between the aromatic amino acids and ^-amino- 

 benzoic acid. As illustrated in Figure 2 mutant strains of Neurospora 

 are known with single deficiencies for each of the aromatic amino acids 

 and for /7-aminobenzoic acid. In addition, a single gene mutation has 

 been found to result in the requirement for all four of these substances. 

 This suggests that all four are derived from a common precursor. (See 

 also 58.) Recent investigations have shown that this common precursor 



HCCHNH^COOH 



COOH 



C-CHN 



hfjCOOH 

 /r6'994 75001 



Figure 2. Biosynthesis of aromatic substances in Neurospora. 



