Fig. 8.

A, Structures and lengths (in angstroms) of the different MTS reagents used in our experiments. Lengths were measured after energy minimization (<0.5 kcal/Å) and represent only the portion of the MTS reagent that covalently modifies an introduced cysteine. Cleavage points of each MTS reagent are indicated by an arrow. B, Summary of the second-order rate constants calculated for MTS derivitization of γ₂D75C-, γ₂A79C-, and γ₂T81C-containing receptors. Oocytes expressing mutant receptors were incubated in the presence of MTS alone (control),MTS + FLZM, MTS + Ro 15-1788, orMTS + GABA. MTS reagents used were as follows: γ₂D75C, MTSEA; γ₂A79C, MTSEA-biotin; γ₂T81C, MTSEA-biotin-CAP. Second-order rate constants were calculated for each MTS reaction and were normalized to the rate measured in the absence of ligand (control). Displayed values are mean ± SD from at least three independent experiments. *,**Indicate values significantly different from control MTS values, with p < 0.05 and p < 0.01, respectively.