State-dependent modification by MTSES at positions 95, 98, and 102. (A) A representative recording for MTSES modification in the absence of ATP for K95C/Cysless channels. (B) A real-time recording with a similar protocol shown in (A) for L102C/Cysless channels. Although very little current was affected by application of MTSES in the absence of ATP, exposure of the same patch to MTSES in the presence of ATP readily diminished the current. (C) Summary of the modification rates for K95C, Q98C, and L102C in the presence of ATP (solid squares). The modification rates in the absence of ATP (crossed circles), were all set at 1 because the modification, if at all, was too slow to be quantified accurately. n = 5 for each construct.