Figure 11.

Expanded version of model in Fig. 9 where the blocker spermine exists in two protonation forms. In the more protonated (more charged) form spermine (SPM) traverses the pore at a low rate (k₋₄ ∼ 10 s⁻¹). K₃ (∼10⁻⁵ M) is the equilibrium dissociation constant for binding of the less protonated (non or much less permeating) form of spermine (SPM*) to the channel (K^b ₁ in Guo and Lu, 2000b). Values of rate constants and valences for other transitions are as in Fig. 9.