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1 While it's very common for biologists and chemists to test whether or not two molecules interact with each other, it's much more useful to gather information on the nature of that interaction. How strong is it? How long will it last? What does this mean for its biological function? These questions can be answered by studying binding affinity. Binding affinity is the strength of the interaction between a single biomolecule and its binding partner, or ligand. It can be quantified, providing information on whether or not molecules are interacting as well as assigning a value to the affinity. Typically, when measuring binding affinity, you're interested in several parameters, but mostly in the unit of measurement called the dissociation constant (K d ), which defines the likelihood that an interaction between two molecules will break. The smaller the dissociation constant, the more tightly bound the ligand is and the higher the affinity is between the two molecules. Binding affinity is an important metric used in both academia and industry. Academic researchers study binding affinity to learn about structural biology, structure-function relationships, and the intermolecular interactions that drive biological processes. On the other hand, drug developers study binding affinity to identify high-affinity molecules that bind to drug targets selectively and specifically. In this case, affinity can guide decisions about the biological relevance of a particular molecule, such as whether the molecule under investigation warrants further screening or characterization. What is binding affinity? The dissociation constant (K d ) defines the likelihood that an interaction between two molecules will break and is a useful measurement to quantify binding affinity.

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