Table 2.
Summary of second-order rate constants for reaction of MTSEA-biotin with introduced sufhydryls
| Receptor | Control | GABA | SR-95531 | 1 mm PB | 50 μm PB | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| k2(M−1s−1) | n | k2(M−1s−1) | n | k2(M−1s−1) | n | k2(M−1s−1) | n | k2(M−1s−1) | n | |
| α1β2-G203C | 257,600 ± 32,700 | 3 | 184,400 ± 14,300 | 3 | 317,700 ± 19,500 | 3 | 579,200 ± 9900* | 3 | 400,100 ± 7300* | 3 |
| α1β2-S204C | 12,060 ± 980 | 5 | 6050 ± 980* | 5 | 3735 ± 310* | 3 | 5656 ± 1180* | 3 | 14,990 ± 3300 | 3 |
| α1β2-Y205C | 955 ± 150 | 5 | 410 ± 15* | 4 | 285 ± 5* | 3 | 870 ± 40 | 3 | ND | 0 |
| α1β2-P206C | 276 ± 41 | 4 | 715 ± 70* | 3 | 398 ± 16 | 3 | 385 ± 25 | 3 | 352 ± 17 | 3 |
| α1β2-R207C | 585 ± 40 | 6 | 100 ± 9* | 4 | 135 ± 10* | 3 | 370 ± 32* | 3 | 690 ± 65 | 3 |
| α1β2-S209C | 120 ± 2 | 4 | 67 ± 11* | 4 | 40 ± 7* | 3 | 77 ± 8* | 3 | 125 ± 3 | 3 |
Second-order rate constants (k2) were calculated by dividing psuedo-first-order rate constants (k1; see Materials and Methods) by the concentration of MTSEA-biotin used during rate experiments, which were as follows: G203C, 1 μm; S204C, 10 μm; Y205C, P206C, and R207C, 200 μm; and S209C, 1 mm. Concentrations of GABA and SR-95531 present during the MTSEA-biotin reaction, which varied according to the affinity of the mutant receptor for each compound, were always between EC60–IC80 for GABA and IC90–IC95 for SR-95531. An asterisk indicates that the rate is significantly different from control (p < 0.01). PB, Pentobarbital; ND, not determined. Values are mean ± SEM.