Table 1.

Parameter values for G-protein activation and receptor phosphorylation

Rate Constant	Definition	Value	References
kon-ag (M−1s−1)	agonist association rate constant	108a	a
koff-ag (s−1)	agonist dissociation rate constant	1 Ğ 2500 b,c	c
kon-antag (M−1s−1)	antagonist association rate constant	108a	a
koff-antag (s−1)	antagonist dissociation rate constant	0.0001 Ğ 1000 b,c	c
khyd (s−1)	GTP hydrolysis rate constant	1 d	d
α	Agonist efficiency	105, 108 d	d
kon-RK (M−1s−1)	receptor kinase association rate constant	1000 e	e
koff-RK (s−1)	receptor kinase dissociation rate constant	1 d	d
kG-recombine (s−1)	G-protein recombination rate constant	1000 f	f
D (cm2/s)	Diffusion coefficient	10−11 Ğ 10 −9 g	g
Concentrations
[L] (M)	ligand concentration	Varied
[R] (#/cell)	Receptor concentration	2×103–2×104 h	h
[G] (#/cell)	G-protein concentration	104 h	h

^aVarying the value of k_on-ag and k_on-antag between 10⁶ and 10¹⁰ M⁻¹s⁻¹ has no noticeable effect on the results. The association rate constant in part determines the time course of receptor-ligand binding reaching equilibrium and under these conditions receptor-ligand equilibrium is reached sufficiently fast to have no noticeable effect on G-protein activation or receptor phosphorylation.

^bthe physiologic range of k_off-ag and k_off-antag is 0.0001 to 100 s⁻¹. We use some values of k_off-ag and k_off-antag larger than 100/sec, but expect that these values would not occur in experimental systems.

^cContreras et al., 1986; Neubig et al., 1988; Waelbroecket al., 1991; Kapur and Seeman, 2000

^dWoolf and Linderman, 2003

^eZhong et al., 2003

^fLee et al., 1993; Sako and Kusumi, 1994

^gMahama and Linderman, 1995; Pardo et al. 1997

^hPardo et al. 1997