 However, eIF2B is able to exchange GDP for GTP only if eIF2 is in its unphosphorylated state.Phosphorylated eIF2, however, due to its stronger binding, acts as an inhibitor of its own GEF (eIF2B).Since the cellular concentration of eIF2B is much lower than that of eIF2, even a small amount of phosphorylated eIF2 can completely abolish eIF2B activity by sequestration.