nKd

nKd is a term encountered in some scientific literature to denote a parameter related to binding affinity or dissociation, but it does not have a single universal definition. Its precise meaning is context-dependent and can vary between fields or even between studies within the same field. In many cases, nKd is used as a shorthand for an apparent or generalized dissociation constant that involves cooperative effects, multiple binding steps, or multivalent interactions.

Common interpretations include: (1) a dissociation constant associated with a system that has n binding sites or n cooperative steps, where the overall binding behavior is described by a model that accounts for multiple interactions; (2) a Hill-type or cooperative binding parameter where n represents the degree of cooperativity, and nKd may refer to an effective affinity derived from a specific equation or fit; and (3) an apparent or reduced dissociation constant obtained under a particular experimental condition or model with an explicit n parameter.

Because there is no universally accepted definition, researchers should verify the exact meaning of nKd in each source. This includes examining the underlying model, the equations used, the meaning of n in that context, and the units reported. When comparing nKd values across studies, it is essential to ensure that the same definition and assumptions are being applied.

See also: dissociation constant (Kd), Hill equation, cooperativity, binding isotherms.