Fig. 1-1. Aromatic amino acid biosynthetic pathway. 

 The common portion of the biosynthetic pathway leading to 

 the branch point intermediate, chorismate, begins with 

 DAHP synthase [1] catalizing the condensation of 

 erythrose 4 -phosphate and phosphoenolpyruvate and 

 consists of seven steps. These steps consist of 

 dehydroquinate synthase [2] , dehydroquinate dehydratase 

 [3] , shikimate dehydrogenase [4] , shikimate kinase [5] , 

 EPSP synthase [6] , and chorismate synthase [7] . 

 Chorismate, at the branchpoint of the pathway is utilized 

 in one direction to yield L-tryptophan (steps 8-12) and 

 in another direction by chorismate mutase [13] to produce 

 prephenate, another branch point intermediate. Organisms 

 in nature use different routings from prephenate. Higher 

 plant chloroplasts proceed through prephenate 

 aminotransferase [14] and arogenate dehydratase [15] to 

 form PHE, or through prephenate aminotransferase and 

 arogenate dehydrogenase [16] to form TYR. In other 

 organisms a second route proceeds through prephenate 

 dehydratase [19] , then through aromatic (or PHE) 

 aminotransferase [20] to synthesize PHE, or through 

 prephenate dehydrogenase [17] and through aromatic (or 

 TYR) aminotransferase [18] to synthesize TYR. 



