Substrate

The chemical reactants to which an enzyme binds are an enzyme's substrate. One enzyme can have one or more substrates, depending on the particular chemical reaction. In some reactions, a substrate can be broken down into several products. In other reactions, multiple substrates can come together to create one product, or become modified.

The location within the enzyme where the substrate binds is called the active site. This site is specific for the substrate. When the substrate binds to the active site, the entire molecule is referred to as the enzyme-substrate complex.

Substrates are very versatile molecules, they can be chemically modified to be conjugated to a certain probe, such as a fluorophore or radioisotope. When an enzyme catalyzes the reaction, the substrate can be converted to a colored product; the probes can be cleaved to release a signal; or the size of the substrate is quantified.