Table 3. Allosteric Parameters for 2 at the δ Receptor^a.

	leu-enkephalin				SNC80				TAN67
	β-arr	GTPγS	cAMP	pERK	β-arr	GTPγS	cAMP	pERK	GTPγS	pERK
logτA	028 ± 0.04	094 ± 006	2.8 ± 0.03	025 ± 016	0.66 ± 0.08	0.56 ± 0.10	0.86 ± 0.03	1.06 ± 0.15	0.67 ± 0.09	0.22 ± 0.07
logτB	−0.73 ± 0.15	0.36 ± 0.17	1.45 ± 0.27	−0.16 ± 0.15	−1.06 ± 0.11	0.29 ± 0.20	1.01 ± 0.02	−0.04 ± 015	0.45 ± 0.07	0.11 ± 0.08
pKA	7.90**	6.6**	6.7*	9.13**	6.38 ± 0.11	7.7*	7.7*	7.7*	7.6*	8.4**
pKB	7.06 ±0.11	5.85 ± 0.23	5.45 ± 0.02	6.13 ± 0.30	6.45 ± 0.05	6.23 ± 0.32	5.52 ± 0.02	5.66 ± 0.30	6.0***	5.80 ± 0.32
log αβ (αβ)	1.18 ± 0.07 (15)	1.67 ± 0.21 (47)	2.80 ± 0.08 (631)	0.99 ± 0.28 (10)	1.33 ± 0.05 (21)	1.00 ± 0.30 (10)	2.11 ± 0.07 (129)	0.89 ± 0.29 (8)	1.11 ± 0.19 (13)	1.41 ± 0.29 (26)

^aValues for affinity, efficacy, and allosteric cooperativity for orthosteric ligands and 2 are derived from the operational model of allosterism. Three different orthosteric agonists were used (leu-enkephalin, SNC80, and TAN67), across up to four functional assays (β-arrestin recruitment, [³⁵S]GTPγS binding, cAMP inhibition, and pERK). In the model τ_A and τ_B represent the efficacy of the orthosteric agonist and allosteric modulator, respectively; pK_A and pK_B represent the binding affinity of the orthosteric agonist and the allosteric modulator, respectively, to the free receptor; and αβ represents the composite allosteric cooperativity factor. Data are presented as the mean ± SEM of three to seven experiments.

^*pK_A is fixed to its equilibrium binding affinity, as ligand is a full agonist in all end points tested.

^**pK_A of leu-enkephalin and TAN67 in end points where they are partial agonists was obtained from fitting their CRC to the operational model of agonism to obtain a functional affinity in each end point tested.

^***the pK_B for TAN67 in [³⁵S]GTPγS binding had to be fixed to the average of the pK_B obtained from Leu-enk and SNC80 as neither allosteric agonism or potentiation reached a limit.