Catalyzes the conversion of chorismate into prephenate via a Claisen rearrangement. chorismate = prephenate kcat is 5.7 sec(-1) (at 30 degrees Celsius). Activity is independent of pH in the range of pH 5-9. Thermostable. The midpoint for its thermal unfolding transition (Tm) is 88 degrees Celsius. Metabolic intermediate biosynthesis; prephenate biosynthesis; prephenate from chorismate: step 1/1. Homodimer.