I have been reading some papers regarding the dynamics of receptor-ligand binding for my project and have come across this term "dynamic affinity" quite often and I am wondering if it actually has a different meaning from just "affinity" and the definition of Kd. Is it possible to define certain parameters affecting the value of Kd that would make it "dynamic"? or is it a different approach to study interactions between proteins.
Hi Virginia, the affinity constant Kd (equilibrium binding constant) is defined as the ratio between the forward and reverse rate constants kf and kr (kf would be the rate at which a receptor ligand complex forms, kr the rate at which the complex dissociates). As a consequence, the value for Kd does not change if both kf and kr are changed proportionally. In other words: a specific affinity of a receptor for its ligand can be the result of slow (low kf and kr) or fast (high kf and kr) rate constants. The latter case is probably what can be defined as a 'dynamic' equilibrium.
Hi Virginia, As indicated before, the addition of the term "dynamic affinity" is simply recognizing that the measured affinity reflects the equilibrium of on and off reactions that provide the observed values. The reasons for using the term may include wanting to have your reader understand the importance of the on and off reaction rates that contribute to the observed equilibrium, especially if your work is measuring influences that are related to a specific aspect of these binding or release mechanisms, especially those that are related to substrate vs product affinities in enzyme binding sites. However, even if the effect you are monitoring simply involves binding occurring in a column or other matrix, you may want to use these terms to point out aspects of your work that are related to these dynamics, especially if they are responsible for a meaningful change in the observed results.
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