Thermodynamics of protein folding 3. Thermodynamics of protein folding, The nati

Question

Thermodynamics of protein folding
3. Thermodynamics of protein folding, The native and denatured forms ofa protein are generally in equilibrium. Protein (denatured) Protein (native) For a certain solution of the protein ribonuclease A, in which the total protein concentration is 20 x 10' M, the concentrations of the denatured and native proteins at 50 and 100 C are listed below. Temperature Protein (denatured) Protein (native) 2.0 x 10 M 5.1 x 10 M 50°C 2.8 x 10" M 1.7 x 10' M 100 C A) Determine AS and AH' for the folding reaction. [Assume these quantities are independent of temperature

Explanation / Answer

As per the equilibrium

Keq = [N] / [D]

Keq = 2X 10^-3 / 5.1 X 10^-6 = 392.15

1) at 50 0 C

so Delta G = -RTlnKeq

Delta G = - 8.314 X (273+50) ln 392.15

Delta G = -16036 joules

Delta G = -16.036 KJ

Similarly

2) at 100 0 C

Delta G = - 8.314 X 373 X ln Keq = 18522 Joules = -18.52 KJ

Assuming that delta S and delta H will not get affected much

Delta G = Delta H - T delta S

at 50 0 C

-16.036 KJ = Delta H - 323 X Delta S

So Delta H = -16.036 + 323 X Delta S ...(1)

at 100 0C

Delta G = Delta H - T Delta S

-18.52 = Delta H - 373 X Delta S

Put equation (1)

-18.52 = -16.036 + 323 X Delta S - 373 Delta S

-2.48 =- Delta S X 50

So Delta S = 0.0496 K J / mol K= 49.6 Joules / mol / K

Putting this value in equation (1)

Delta H = -16.036 + 323 X Delta S = -16.036 + 323 X 0.0496 = -0.0152 KJoules / mole

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