Which binding parameter can be defined as the inverse of Ka?

The correct choice, which is defined as the inverse of Ka, is the dissociation constant, Kd. The association constant, Ka, represents the affinity of a ligand for its binding site, quantifying how readily the ligand associates with the target. Conversely, the dissociation constant Kd indicates how readily the complex dissociates into its components. Mathematically, Kd is expressed as the ratio of the dissociation rate constant to the association rate constant, and it reflects the concentration at which half of the binding sites are occupied by the ligand.

In practical terms, a lower Kd value indicates a higher affinity of the ligand for the binding site, while a higher Kd signifies lower affinity. This relationship is pivotal in biochemistry as it provides insights into interactions between molecules, like enzymes and substrates or receptors and ligands. Understanding this distinction allows researchers to better interpret binding studies and the dynamic equilibrium between bound and unbound states in biochemical processes.