Table 2.

Summary of second-order rate constants for reaction of MTSEA-biotin with introduced sufhydryls

ReceptorControlGABASR-955311 mm PB50 μm PB
k2(M−1s−1)nk2(M−1s−1)nk2(M−1s−1)nk2(M−1s−1)nk2(M−1s−1)n
α1β2-G203C257,600  ± 32,7003184,400  ± 14,3003317,700  ± 19,5003579,200  ± 9900*3400,100  ± 7300*3
α1β2-S204C12,060  ± 98056050  ± 980*53735  ± 310*35656  ± 1180*314,990  ± 33003
α1β2-Y205C955  ± 1505410  ± 15*4285  ± 5*3870  ± 403ND0
α1β2-P206C276  ± 414715  ± 70*3398  ± 163385  ± 253352  ± 173
α1β2-R207C585  ± 406100  ± 9*4135  ± 10*3370  ± 32*3690  ± 653
α1β2-S209C120  ± 2467  ± 11*440  ± 7*377  ± 8*3125  ± 33
• 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.