The abc (region of a protein) of xyz (protein name) binds the 50kDa ZYX (protein name) with dissociation constant (kDa) of 30nM.
Can one explain what does this dissociation constant mean and what information froths sentence one can get?
Dissociation constant is an equilibrium constant that measures the affinity of the interaction between the two proteins. The equilibrium is AB A + B and the dissociation constant Kd = [A]free[B]free/[AB]. It has units of concentration. The Kd can vary depending on environmental conditions, such as pH, ionic strength, and temperature. You can use the Kd to calculate the concentration of each of the components (A, B, and AB) at equilibrium, given a set of starting concentrations [A]total and [B]total.
[A]total = [A]free + [AB]
[B]total = [B]free + [AB]
[A]free = [A]total - [AB]
[B]free = [B]total - [AB]
[AB]Kd = ([A]total - [AB])([B]total - [AB])
and so forth, leading to a quadratic equation in which [AB] is expressed in terms of [A]total, [B]total and Kd. Once you calculate [AB], you can also calculate [A]free and [B]free.
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