2.3.1.7 4 9 - 487400 2.3.1.7 4.5 8.5 - 487400 2.3.1.7 5.5 10 - 486295 2.3.1.7 6 9 activity declines rapidly on either side of the optimum pH 487422 2.3.1.7 6 10 - 487416 2.3.1.7 7 9 - 487418