Percent conductance change and rates of reaction for uncharged MTS reagents in single-channel experiments on TH6–TH7 segment mutant channels
| Mutant | cis/trans pH | MTS reagent | Conductance change (%) | Waiting time (cis) | Waiting time (trans) | kcis | ktrans |
| s | s | M−1 s−1 | M−1 s−1 | ||||
| T301C | 6.6/7.2 | Glucose | −11 ± 1 (n = 6) | 70 ± 61 (n = 6) | >535a (n = 3) | 14 | <2 |
| A303C | 7.0/7.0 | Glucose | −100 ± 0 (n = 10) | 58 ± 33 (n = 10) | NE (n = 4) | 17 | NE |
| S305C | 7.0/7.0 | Glucose | −79.2 ± 0.8 (n = 9) | 2.8 ± 2.2 (n = 6) | 65 ± 40 (n = 4) | 351 | 15 |
| I306C | 6.6/7.2 | Glucose | −36 ± 2 (n = 3) | 63 ± 43 (n = 8) | NE (n = 6) | 16 | NE |
| L307C | 5.3/7.2 | Glucose | −59 ± 5 (n = 42) | 101 ± 95 (n = 4) | 2.4 ± 2.2 (n = 42) | 10 | 421 |
| G309C | 5.3/7.2 | Glucose | −33 ± 4 (n = 55) | NE (n = 5) | 2.4 ± 3.1 (n = 56) | NE | 413 |
| S312C | 6.0/8.0 | ACE | −33 ± 3 (n = 6) | 54 ± 50 (n = 4) | 18 ± 4 (n = 3) | 18 | 57 |
| “ | “ | Glucose | −39 ± 3 (n = 4) | 641 ± 56 (n = 2) | 118 ± 1 (n = 2) | 2 | 8 |
| G315C | 6.0/8.0 | ACE | −70 ± 1 (n = 5) | 190 ± 89 (n = 2) | 267 ± 136 (n = 3) | 5 | 4 |
| “ | 7.0/7.0 | Glucose | −77 ± 3 (n = 3) | 5.6 ± 0.6 (n = 3) | NE (n = 5) | 179 | NE |
| Mutant | cis/trans pH | MTS reagent | Conductance change (%) | Waiting time (cis) | Waiting time (trans) | kcis | ktrans |
| s | s | M−1 s−1 | M−1 s−1 | ||||
| T301C | 6.6/7.2 | Glucose | −11 ± 1 (n = 6) | 70 ± 61 (n = 6) | >535a (n = 3) | 14 | <2 |
| A303C | 7.0/7.0 | Glucose | −100 ± 0 (n = 10) | 58 ± 33 (n = 10) | NE (n = 4) | 17 | NE |
| S305C | 7.0/7.0 | Glucose | −79.2 ± 0.8 (n = 9) | 2.8 ± 2.2 (n = 6) | 65 ± 40 (n = 4) | 351 | 15 |
| I306C | 6.6/7.2 | Glucose | −36 ± 2 (n = 3) | 63 ± 43 (n = 8) | NE (n = 6) | 16 | NE |
| L307C | 5.3/7.2 | Glucose | −59 ± 5 (n = 42) | 101 ± 95 (n = 4) | 2.4 ± 2.2 (n = 42) | 10 | 421 |
| G309C | 5.3/7.2 | Glucose | −33 ± 4 (n = 55) | NE (n = 5) | 2.4 ± 3.1 (n = 56) | NE | 413 |
| S312C | 6.0/8.0 | ACE | −33 ± 3 (n = 6) | 54 ± 50 (n = 4) | 18 ± 4 (n = 3) | 18 | 57 |
| “ | “ | Glucose | −39 ± 3 (n = 4) | 641 ± 56 (n = 2) | 118 ± 1 (n = 2) | 2 | 8 |
| G315C | 6.0/8.0 | ACE | −70 ± 1 (n = 5) | 190 ± 89 (n = 2) | 267 ± 136 (n = 3) | 5 | 4 |
| “ | 7.0/7.0 | Glucose | −77 ± 3 (n = 3) | 5.6 ± 0.6 (n = 3) | NE (n = 5) | 179 | NE |
The percent conductance change (combining both cis and trans MTS effects) is given as mean ± SD, with n being the number of single-channel reactions that were used in calculating each value. Likewise, the waiting times to reaction (adjusted to reflect a 1-mM MTS concentration) are given as τ ± στ. Although we do not make use of the second-order rate constant, k = 1/(τ × 1 mM), obtained from single-channel experiments, its value is given for comparison with values in the other tables. For the most part, τ and στ are approximately equal, as expected for exponentially distributed waiting times. The interested reader can estimate the SD of k as the value of k given in the table times n/[(n − 1)(n − 2)1/2], based on the assumption that the waiting times are exponentially distributed and hence the reciprocal of a sum of waiting times follows an inverse-gamma distribution (Johnson et al., 1994; Schraiber et al., 2013). The percent conductance change and waiting time could not always both be determined for a given reaction event, so the n values for the cis- and trans-side waiting times do not necessarily add up to the n value given for the conductance change. The concentrations of MTS-glucose and MTS-ACE were in the range 30 µM to 1 mM and 1 to 2 mM, respectively. NE, no effect.
For T301C with trans MTS-glucose, of three channels observed, only one reacted, apparently while in a long-lived closed state, after 8–11 min. The channels that did not react were exposed to 1 mM MTS-glucose for about 10 min each.