Simulation of ligand directed signaling for a receptor in equilibrium with two different G proteins at the same time (a-d; dynamic equilibrium case) or independently (e-h; segregated equilibrium case). In each case, the microscopic affinity constant of agonist A for the two active states of the receptor (R

^{*} and R

^{**}) was the same (

*K*_{b} =

*K*_{c} = 10

^{9}), whereas agonist B exhibited selectivity for R

^{*} (

= 10

^{9}) compared with R

^{**} = 10

^{8}). The microscopic affinity constants of the agonists for the ground state of the receptor (R) were the same (

*K*_{a} =

= 10

^{5}). The theoretical curves for the quaternary complex (a, c, e, and g) were generated using eqs. 31 and 32 under

*Appendix* with the ratio of

*G*_{1}/R =

*G*_{2}/R = 10 except in e, where

*G*_{2}/R = 0 and in

*g* where

*G*_{1}/R = 0. The theoretical concentration response curves for the agonists in panels b, d, f, and h were generated from the operational model (percentage response = (100 ×

*S*^{m})/(

*S*^{m} +

*K*_{E});

*K*_{E} = 0.03;

*m* = 2) with the value for quaternary complex in a, c, e, and g substituted in for the stimulus (

*S*), respectively. The values of the other microscopic constants in eqs. 31 and 32 were as follows:

*K*_{e} = 7 × 10

^{-3},

*K*_{f} = 7 × 10

^{-3},

*K*_{g} = 7 × 10

^{2},

*K*_{h} = 7 × 10

^{2},

*K*_{i} = 7 × 10

^{2},

*K*_{j} = 7 × 10

^{2},

*K*_{k} = 1 × 10

^{8},

*K*_{l} = 1 × 10

^{8},

*K*_{m} = 4 × 10

^{4},

*K*_{n} = 8 × 10

^{2},

*K*_{o} = 8 × 10

^{2},

*K*_{p} = 4 × 10

^{4},

*K*_{q} = 8 × 10

^{-6}, and

*K*_{r} = 8 × 10

^{-6}. The concentration of GTP (

*X*) was 1 mM.

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