Blockade of E166A and E166Q by various amphiphilic reagents. (A) Comparison of the steady-state K_1/2 of various fatty acids in the E166A and E166Q mutants. V_m = −140 mV. The horizontal axis represents the carbon number (or the length of the hydrophobic tail) in these compounds: 3 carbons (PA); 4 carbons (BA); 6 carbons (HA); 8 carbons (OA); 10 carbons (DeA); 12 carbons (DoA). (B) Comparison of the steady-state blocking affinities of fatty acids and alkyl sulfonates in the E166A mutant. V_m = −140 mV. The alkyl sulfonate compounds are structurally similar to fatty acids except that the charged end is a SO₃⁻ group. (C) The E166A mutant is also sensitive to SDS. Both recordings were obtained from the same patch.