sentence: Assuming that ( 1 ) the difference between two systems only locally affects the PMF for PT in E148A when the glutamate is bound to S ( corresponding to the E148 down conformation in the WT PMF with Cl absent in Figure 3 ) and ( 2 ) the binding of the glutamate in the E148A mutant is destabilized by ∼ 3 – 4 kcal / mol compared to WT , decreasing the free energy barrier for PT via glutamate , then the rate constant would be ∼ 150 – 780-fold greater than that in WT , allowing the H flux in the E148A mutant to be observed in experiment .