Table 1.

EC₅₀ for selected Trp mutants at α86, α184, and γ55/δ57, showing that all three sites are substantially insensitive to the electronic properties of the Trp side chain

Side chain*	EC50,† μM
	α86	α184	γ55/δ57‡
Trp	50	50	50
5-Br-Trp	53	48	23
5-CN-Trp	61	46	25
4,5,6,7-F4-Trp	45	62	92

^*See Fig. 2 for side-chain structures. 

^†Hill coefficients are all in the range 1.5–2.0. 

^‡For all studies of this Trp, mutations were introduced into both the γ55 and δ57 sites, and both mutant subunits were expressed, so both agonist binding sites have the mutant Trp.