Two-State Protein Melting Curve (N, P, T Ensemble)
Two-State Protein Melting Curve (N, P, T Ensemble)
This Demonstration illustrates the fraction () of a two-state protein (or other biomolecule) that has melted at temperature . The two states of the protein are denoted (native or folded) and (denatured or melted) and we consider the dynamic equilibrium . The ratio of the two states' equilibrium concentrations is =exp[-ΔG°/(RT)], where ) is the standard state Gibbs free energy difference and is the universal gas constant (8.314 J/mol-K). Melting occurs when (i.e., ). . The parameter (standard state enthalpy difference) controls the steepness of the transition, but does not affect the location of the point where . The temperature () at which is and .
Q
T
N
D
N⇌D
[D]
[N]
ΔG°(=ΔH°-TΔS°
R
ΔG°=0
[D]=[N]
Q≡===
[D]
[N]+[D]
-1
1+
[N]
[D]
-1
(1+exp[ΔG°/(RT)])
-1
(1+exp[(ΔH°-TΔS°)/(RT)])
ΔH°
Q=0.5
T
Q=0.5
T
m
ΔS°=ΔH°/
T
m