Table 1. Concentration dependence of the covalent reaction at mutant receptors at the binding level.

mutated receptor	mutation homologous to	EC50 (µM)
α1S204Cβ2γ2		n.r.
α1S205Cβ2γ2		0.63±0.18
α1T206Cβ2γ2		0.082±0.028
α2S204Cβ2γ2	α1S204C	3.2±2.3
α2S205Cβ2γ2	α1S205C	6.6±5.4
α2T206Cβ2γ2	α1S206C	0.19±0.056
α5T208Cβ1γ2	α1S204C	0.39±0.21
α5S209Cβ1γ2	α1S205C	4.1±2.2
α5T210Cβ1γ2	α1S206C	0.45±0.15
α6S203Cβ2γ2	α1S204C	n.r. a
α6N204Cβ2γ2	α1S205C	n.r. a
α6T205Cβ2γ2	α1S206C	5.4±0.80a

Left column: mutated receptors. Middle column: homology of the mutations to α₁. Right column EC₅₀ is given as mean ±SD for three to four experiments where each point in the dose-response curve was determined in triplicates. The receptors were exposed to increasing concentrations of 3-NCS compound for 30 min on ice and extensively washed. Residual binding was determined using [³H]Ro15–1788 as radioactive ligand and converted to percentage of binding sites covalently reacted. All wild type receptors showed no covalent reaction. n.r.: no covalent reaction.

^a[³H]15–4513 was used as a radioactive ligand.