An enzyme is typically a protein-based substance that facilitates the occurrence of a metabolic reaction by interacting with and transforming a drug or chemical to one or more specific metabolites. A drug or chemical that interacts with a particular enzyme is a substrate of the enzyme. An enzyme subsequently binds and metabolizes different substrates with varying affinities or binding strengths. The metabolic reaction type and metabolites produced depend on the specific enzyme that interacts with a certain drug or chemical.

Each enzyme in DrugBank is considered a [bio entity] and is associated with a unique identification code that starts with "BE". For example, the code for Cytochrome P450 2D6 is BE0002363. 

Note that targets, enzymes, carriers, and transporters may switch roles depending on the drug to which they bind based on each drug's unique pharmacodynamic and pharmacokinetic profiles.