Table 3. Binding Kinetics of GLP-1 and GLP-1 Val8 at GLP-1R^a.

				koff (n = 3)
ligand	affinity pKD (n = 3–4) (homologous)	affinity pKi (n = 3) (heterologous)	kobs (n = 3–4) (min–1)	fast (min−1)	% fast phase	slow (min−1)	Bmax (homologous) (n = 3–4) (fmol/10.000 cells)	Bmax (kinetics) (n = 3–4) (CPM/pM)
GLP-1	8.3 ± 0.1	8.6 ± 0.2b	0.054 ± 0.007	0.014 ± 0.001	53 ± 3	0.0023 ± 0.0003	53 ± 20	11.3 ± 1.30
GLP-1 Val8	8.2 ± 0.1	8.0 ± 0.1c*	0.029 ± 0.005*	0.052 ± 0.008**	49 ± 5	0.0026 ± 0.0010	20 ± 8	0.762 ± 0.08****

^aAll data were fitted with the three-parameter logistic curve to obtain pIC₅₀ and B_max. pIC₅₀ represents the negative logarithm of the half maximal inhibitory concentration in molar. The association data were analyzed through a one-phase association model, whereas the dissociation data were best fitted with a two-phase decay model. B_max values are calculated using the homologous competition binding results with different concentrations of [¹²⁵I]GLP-1 (Val8). Kinetic B_max was calculated by taking the saturation point in CPM (plateau) of the association curve and the CPM value at zero minutes from the dissociation curve. Statistical significance was assessed using an unpaired two-tailed t-test (*P < 0.05; **P < 0.01; ****P < 0.0001; as compared to the GLP-1 response).

^bRadioligand [¹²⁵I]GLP-1 Val8.

^cRadioligand [¹²⁵I]GLP-1. Data represent the mean ± s.e.m. of n independent experiments performed in triplicate or duplicate (homologous and heterologous binding).