Involved in the biosynthesis of the siderophore enterobactin (macrocyclic trimeric lactone of N-(2,3-dihydroxybenzoyl)-serine). Catalyzes the reversible conversion of chorismate to isochorismate. chorismate = isochorismate Siderophore biosynthesis; enterobactin biosynthesis. Monomer. Belongs to the isochorismate synthase family.