H(+) + prephenate = 3-phenylpyruvate + CO2 + H2O Allosterically regulated by all of the three aromatic amino acids (phenylalanine, tyrosine and tryptophan). Inhibited by low concentrations of aromatic amino acids and highly activated at higher concentrations. Ionic interactions are required for optimal activity. Optimum pH is 6-7. Optimum temperature is 37-42 degrees Celsius. Amino-acid biosynthesis; L-phenylalanine biosynthesis; phenylpyruvate from prephenate: step 1/1. Homodimer. Both domains are absolutely required for activity. In the absence of the ACT domain, the enzyme not only loses its regulatory activity, but also its catalytic activity. Was identified as a high-confidence drug target.