Pfizer Handbook of Microbial Metabolites 



318 



tioned that N-fructosylanthranilic acid has been isolated from 

 a yeast. Probably indole never exists in the free state to any 

 appreciable extent during the tryptophan synthesis, but is en- 

 zyme-bound. 



Ribose contributes also to the biosynthesis of histidine. Here 

 purines are catalytic, furnishing a carbon atom and a nitrogen 

 atom from the pyrimidine ring to form positions 2 and 3 of the 

 histidine ring. The purine is then regenerated by reaction with 

 a Ci substance. Adenine is the most efficient purine for this 

 purpose. The following scheme has been worked out, largely 

 on the basis of auxotroph work: (P = phosphate, R = ribose). 



HO 



CH, 



I 

 CH2— CH— CH— CH 



NH2 



I Ribose-5- vik ^ 



^j:?:\^N. phosphate | ^^ 



I iT )> ^ CH2— CH— CH— CH I 



NH2 



ATP 



P— O OH OH OH 



R— P 

 Adenosine 

 Monophosphate 



Ci substance, 

 reamination 



R— P 

 Glutamine 



HC- 



CH>— CH— CH— C- 



P— O OH OH 



4-(D-ery tfiro- 1 ',2'-dihydroxy- 

 3'-phosphopropyl) imidazole 

 (Imidazoleglycerol Phosphate) 



R— P 



5-Amino-l-D- 



(5'-phospho- 



ribosyl)-4- 



imidazolecarboxamide 



Some chemicals which inhibit purine synthesis also cause ac- 

 cumulation of such intermediates. To continue with the bio- 

 synthesis of histidine: 



