Table 1. Association and dissociation kinetics of Nb39 to µ-OR-rHDL in the presence of various agonists.

k_obs and k_off were determined for each independent experiment (number of individual experiments indicated in ‘n’ column) and averaged. One-phase association and single-phase exponential decay models were used. Half-time values (t_1/2) numbers were calculated from the respective k values (t_1/2 = 0.693/k). A one-way ANOVA was performed followed by a Tukey post-hoc test. Methadone was found to be statistically different compared to all other orthosteric ligands other than loperamide and PZM21. Both loperamide and PZM21 were also found to be statistically different from several other ligands, though not as many as methadone.

Ligand	kobs ± SEM (min−1)	t1/2ass (sec)	koff (min−1)	t1/2dis (sec)	N
BU72	0.20 ± 0.01	3.5	0.031 ± 0.001	22	14
DAMGO	0.179 ± 0.008	3.9	0.030 ± 0.001	23	6
Leu-Enk	0.098 ± 0.02	7.1	0.031 ± 0.001	23	9
L-Methadone	0.19 ± 0.02	3.6	0.052 ± 0.003	13	6
Morphine	0.08 ± 0.01	8.5	0.033 ± 0.003	21	7
Nalbuphine	0.023 ± 0.008	30	0.036 ± 0.004	19	11
PZM21	0.064 ± 0.004	11	0.043 ± 0.002	16	6
Endomorphin 2	0.101 ± 0.002	6.9	0.036 ± 0.002	19	6
Loperamide	0.208 ± 0.009	3.2	0.044 ± 0.003	16	6
Oxycodone	0.044 ± 0.001	16	0.028 ± 0.001	25	9
Etorphine	0.180 ± 0.007	3.9	0.026 ± 0.001	27	6
Fentanyl	0.075 ± 0.005	9.2	0.035 ± 0.002	20	6
Met-Enk	0.131 ± 0.004	5.3	0.027 ± 0.001	26	6
Hydrocodone	0.042 ± 0.004	17	0.029 ± 0.001	24	6
Buprenorphine	0.058 ± 0.009	12	0.025 ± 0.001	27	6
Naloxone	n/a	----	n/a	----	3
Diprenorphine	n/a	----	n/a	----	3
BMS-986122	0.012 ± 0.001	56	0.027 ± 0.003	25	10
BMS-986187	0.025 ± 0.006	28	0.037 ± 0.005	19	11