Allostery — Monod-Wyman-Changeux (MWC) Model
Two-state allosteric proteins: T (tense/inactive) ↔ R (relaxed/active) conformational equilibrium
MWC Parameters
Subunits n:
4
Allosteric constant L = [T₀]/[R₀]:
1000
Affinity ratio c = K_R/K_T:
0.01
Effectors
Activator [A] (stabilizes R):
0.0
Inhibitor [I] (stabilizes T):
0.0
K_A (activator affinity for R):
1.0
K_I (inhibitor affinity for T):
1.0
Theory
MWC saturation function:
Ȳ = [α(1+α)^(n−1) + Lcα(1+cα)^(n−1)] /
[(1+α)^n + L(1+cα)^n]
where α = [S]/K_R
L_eff = L·[(1+[I]/K_I)/(1+[A]/K_A)]^n
Hill coeff: n_H = ∂log(Ȳ/1−Ȳ)/∂log[S]
Max n_H ≤ n (number of subunits)
Cooperativity from T↔R switch,
not direct subunit interaction