Chemical specificity

Chemical specificity is the ability of a protein's binding site to bind specific ligands. The fewer ligands a protein can bind, the greater its specificity.

Specificity describes the strength of binding between a given protein and ligand. This relationship can be described by a dissociation constant, which characterizes the balance between bound and unbound states for the protein-ligand system. In the context of a single enzyme and a pair of binding molecules, the two ligands can be compared as stronger or weaker ligands (for the enzyme) on the basis of their dissociation constants. (A lower value corresponds to a stronger binding.)

Specificity for a set of ligands is unrelated to the ability of an enzyme to catalyze a given reaction, with the ligand as a substrate

If a given enzyme has a high chemical specificity, this means that the set of ligands to which it binds is limited, such that neither binding events nor catalysis can occur at an appreciable rate with additional molecules.

An example of a protein-ligand pair whose binding activity can be described as highly specific is the antibody-antigen system. Conversely, an example of a protein-ligand system that can bind substrates and catalyze multiple reactions effectively is the system, which can be considered a promiscuous enzyme due to its broad specificity for multiple ligands.

Enzyme specificity refers to the interactions between any particular enzyme and its corresponding substrate. The interactions between the enzyme and substrate thus substantially affect the specificity between the two entities. Electrostatic interactions and Hydrophobic interactions are known to be the most influential in regards to where specificity between two molecules is derived from. The strength of these interactions between the enzyme and substrate positively correlate with their specificity for one another.

Aside from interactions, the actual conformation or shape of the enzyme affects what particular substrates are able to bind to it. The enzyme's shape complementarity for its substrate is crucial in ensuring the substrate is in the correct proximity and orientation in order for the enzyme to successfully bind its substrate. These conformational restrictions are known as induced fit and lock-key model.

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