Figure 6.

Single channels formed by the colicin Ia carboxy-terminal fragment, 282–626. Before the start of each record, 46 ng of mutant “−3” C/CT-XL (without a His-tag) were added to the cis compartment. (The colicin mutant was biotinylated via a maleimide linker, but streptavidin was not used for these experiments.) (A) A single channel opens to the normal conductance (44 pS), and then drops to a low-conductance state (9 pS). The voltage was held at +80 mV for the duration of this record. (B) A channel that has already passed through the normal conductance state is shown in the low-conductance state (8 pS) at the beginning of the record. When the voltage was switched to −80 mV, the channel flickered once (the conductance at this voltage is only 1.6 pS) and closed. After the return to +80 mV, the channel reopened directly to the low-conductance state, apparently without passing through the normal conductance state. The solution on both sides of the membrane was the same as in Fig. 5, with the addition of 2.6 mM tris(2-carboxyethyl)-phosphine. The records were filtered at (A) 30 Hz and (B) 10 Hz.