Effect of MTS-reagents on [3H]MFZ 2-12 binding. Membrane preparations of the cysteine mutants were incubated with 0.25 mM MTSEA, 1 mM MTSET or 10 mM MTSES for 2 min at RT, and washed, prior to [3H]MFZ2-12 binding assay, as described in Methods. The remaining binding activity is shown as % of control (no MTS-reagent). The binding activity of a large number of mutants in TM6-IL3-TM7 was greatly inhibited by the MTS-reagents. *, ** and *** indicate significantly different (p < 0.05, p < 0.01 and p< 0.001, respectively) from X7C by One-way ANOVA with Dunnett's post hoc test.