Table 2

Change in binding energy caused by the mutation T196A

	Adenylyl cyclase stimulation
	EC_{50 (WT)}	EC_50(T196A)	EC_50(T196A)		Δ(ΔG)
	EC_{50 (WT)}	EC_50(T196A)	EC_50(WT)		Δ(ΔG)
	nm			kJ/mol
5-HT	74	540	7.3	5.1
LSD	16	290	18.1	7.5

	[³H]-LSD binding assays
	K_i(d)(WT)	K_i(d)(T196A)	K_i(d)(T196A)		Δ(ΔG)
	K_i(d)(WT)	K_i(d)(T196A)	K_{i(d) (WT)}		Δ(ΔG)
	nm			kJ/mol
5-HT	168.2	992.5	5.9	4.6
[³H]LSD	1.9	32.0	16.8	7.3
Lisuride	10.9	372.7	34.2	9.1
Ergotamine	2.4	38.6	16.1	7.2
Methysergide	289.8	41.0	0.14	−5.0
Mesulergine	2662.9	725.0	0.27	−3.4

The change in free energy [Δ(ΔG) = R T ln (EC_50(T196A)/EC_50(WT))] for the interaction of 5-HT and LSD with wild-type 5-HT₆ receptor and mutant T196A was calculated from the EC₅₀ values determined in adenylyl cyclase assays and from the K_i orK_d values measured in [³H]LSD binding assays for all ligands that showed significant changes in their affinities.

WT, wild-type.