Catalyzes the conversion of chorismate to isochorismate. Can also catalyze the reverse reaction, but with a lower efficiency. chorismate = isochorismate Binds more tightly in the presence of chorismate. kcat is 213 min(-1) for mutase activity with chorismate. kcat is 176 min(-1) for mutase activity with chorismate in the presence of 30 mM of beta-mercaptoethanol (BME). kcat is 144.9 min(-1) for mutase activity with chorismate (at pH 7.5 and 37 degrees Celsius). kcat is 80 min(-1) for mutase activity with chorismate in the absence of 30 mM of beta-mercaptoethanol (BME). kcat is 3.8 min(-1) for mutase activity with isochorismate (at pH 7.5 and 37 degrees Celsius. Optimum pH is between 7.5 and 8. The mutase activity decreases sharply at pH 6.5 and 9 to about 20% of that observed at the optimum pH. Optimum temperature is 37 degrees Celsius. At 60 degrees Celsius the mutase activity is completely lost. Quinol/quinone metabolism; 1,4-dihydroxy-2-naphthoate biosynthesis; 1,4-dihydroxy-2-naphthoate from chorismate: step 1/7. Quinol/quinone metabolism; menaquinone biosynthesis. Homodimer. Mutant produces only a trace of menaquinone. Belongs to the isochorismate synthase family.