sentence: Several key steps in the Cl / H exchange process were proposed based on these and other experimental findings : ( 1 ) E148 ( Glu ) and E203 ( Glu ) participate in the PT process , although Glu at position 203 is not essential for PT in ClC-ec1 and other ClC proteins , and ( 2 ) protonation of E148 opens the extracellular gate and allows Cl transport , and ( 3 ) the Cl and H transport pathways overlap from E148 to the extracellular solution , as shown in Figure 1 , but diverge below E148 .