Question

Dissociation constant of K_d for antibody and antigen interaction is 1.0 nM (notice it is a miscall), calculate the molar change in free energy of binding (or association) DG^o_binding.

Answer 1

Given above is the dissociation constant for antibody and antigen interaction,

Kd = 1.0 nM

To calculate molar change in free energy

Ka = 1/Kd = 1/1.0 = 1.0

dGo(binding) = -RTlnKa

with,

R = gas constant

T = 25 oC + 273 = 298 K

we get molar free energy of binding,

dGo(binding) = -8.314 x 298 ln(1.0)

                      = 0 kJ/mol

So, the molar free energy change in this case is zero.