SYNTHESIS OF AMINO-ACIDS 



71 



The relationships of these compounds to ornithine has still 

 to be fully elucidated [lyb]. The conversion of glutamic 

 acid to ornithine probably proceeds via N-acetylglutamic 

 acid — > N-acetylglutamic acid y-semialdehyde — > a-N- 

 acetylornithine — > ornithine [see id]. 



Tryptophan and nicotinic acid 



The interrelationships betv^een tryptophan, the other 

 aromatic amino-acids and nicotinic acid, as revealed by 

 experiments with N. crassa and Esch. coli, are summarized in 

 Fig. 5.2. Initially, two tryptophanless mutants oi Neurospora 

 (10575 ^^^ 40008) were isolated, both utilized indole in 

 place of tryptophan but only one (40008) utilized anthranilic 



COCH2Ch(nH2)cOOH 



p-amirtobcnzoic acid 



phenylolanine 



tyrosine 



nicotinic ecid 



FIG. 5.2. — The tryptophan cycle and the synthesis of nicotinic acid 

 in Neurospora crassa. Compounds A and B are hypothetical 

 intermediates, and the details of the relationship between 

 tryptophan and the other aromatic amino-acids and PAB are 

 not yet known (see pp. 72-3) [24] 

 6 



