Catalyzes the Claisen rearrangement of chorismate to prephenate. May sequester with cyclohexadienyl dehydratase and an aromatic aminotransferase to form phenylalanine or phenylpyruvate. chorismate = prephenate kcat is 9.7 sec(-1) for chorismate. Metabolic intermediate biosynthesis; prephenate biosynthesis; prephenate from chorismate: step 1/1. Homodimer.