Are Binding Free Energy and Binding Affinity the Same? Understanding the Difference

No, binding free energy and binding affinity are not physically equivalent or interchangeable terms, although they are related. Here's why:

Binding Affinity:

Binding affinity describes how strongly a ligand (like a drug) binds to its target (like a receptor). Imagine it as a measure of how much the ligand 'wants' to stick to its target.

Binding Free Energy:

Binding free energy is a thermodynamic concept. It quantifies the change in free energy when a ligand and target combine. This considers factors like heat changes (enthalpy) and changes in disorder (entropy) during binding.

The Key Difference:

Think of it like this:

• Binding affinity tells you how tightly two things are held together.
• Binding free energy tells you how stable that connection is in terms of energy.

In Summary:

Both terms relate to how strongly a ligand interacts with its target, but they provide different information. Binding affinity focuses on the interaction's strength, while binding free energy focuses on the thermodynamic stability of the resulting complex. Understanding this difference is crucial in fields like drug discovery, where researchers need to assess both the strength and stability of drug-target interactions.