Analysis of results for the TH8–TH9 segment. (A) Helical-wheel diagram based on the results of Huynh et al. (1997) for T-domain segment TH8. The effect of MTS-EA on single-cysteine mutants is indicated. Plain boxed labels, positions at which MTS-EA reaction caused a decrease in single-channel conductance; boxed labels with a black background, positions at which MTS-EA reaction caused an increase in single-channel conductance and an increase in flickering; plain labels, no effect of MTS-EA. The dashed line, based on spin-label studies, divides lipid-exposed residues (right side) from protein-exposed residues (left side) (Zhan et al., 1995; Oh et al., 1999a). (B) Plot of the relative accessibility value, f, against residue number for the T-domain TH8–TH9 segment. Based on macroscopic experiments using MTS-ET (▼, ▽) or MTS-glucose (□), f was calculated as in Fig. 9. Also as in Fig. 9, closed symbols are used for residues that were observed to react primarily in the open state; open symbols are used for the other residues. The sign of the voltage in the MTS-ET experiments was such as to promote MTS-ET entry into the channel. This panel is based on data in Table 5. The error bars represent the SD of f.