Catalyzes the Claisen rearrangement of chorismate to prephenate (By similarity). Acts at the first branch point in the aromatic amino acid pathway where it steers biosynthesis towards phenylalanine and tyrosine, and away from tryptophan (By similarity). chorismate = prephenate Each dimer has two allosteric binding sites that can bind the regulatory effectors tryptophan or tyrosine (By similarity). Can bind either one tryptophan or one tyrosine, two tryptophan or two tyrosine or one tryptophan and one tyrosine, which differentially affect the catalytic activity (By similarity). Activated by tryptophan and subject to feedback inhibition by tyrosine (By similarity). In the presence of both tryptophan and tyrosine, the enzyme is in the activated state (By similarity). Metabolic intermediate biosynthesis; prephenate biosynthesis; prephenate from chorismate: step 1/1. Homodimer.