FIGURE 4.

Single-channel electrical recordings of the membrane-extracted FhuAΔC/Δ4L protein (mFhuAΔC/Δ4L). A, step increase of the electrical current showing a single-channel insertion of the mFhuAΔC/Δ4L into the lipid bilayer. Protein was added to the cis side. The transmembrane potential was +40 mV. B, single-channel electrical trace of mFhuAΔC/Δ4L at an applied transmembrane potential of +40 mV. The expanded trace illustrates the signature of the channel at a greater time resolution. C, histogram of the probability (P(G)) of the occurrence of a given single-channel conductance of mFhuAΔC/Δ4L. D, current-voltage (I/V) relationship of a single mFhuAΔC/Δ4L protein pore. The standard error bars are determined from at least three separate single-channel experiments. E, voltage ramp acquired with two mFhuAΔC/Δ4L protein pores. Other pores either inserted or closed during the measurement at a greater transmembrane potential. The slope of the voltage ramp was 1.4 mV s⁻¹. Single-channel electrical recordings were performed in 1 m KCl, 10 mm phosphate buffer, pH 7.4. The single-channel electrical trace was low pass Bessel-filtered at 2 and 1 kHz in B and E, respectively.