Enzymes are proteins that change the chemical properties of other molecules. It does this by catalyzing a reaction. The enzyme has an active site that is specific for a certain molecule, or substrate. When the enzyme and substrate bind, a reaction takes place. The effect on the substrate depends on the type of enzyme. Generally, there are six types of enzymes.
Oxidoreductases
Oxidoreductases are enzymes that transfer electrons in the form of hydride ions or hydrogen atoms.
Transferases
Transferases are a group of enzymes that catalyze group transfer reactions. This involves the transfer of a group of atoms from one molecule to another. An example would be moving a phosphoryl group from ATP to glucose.
Hydrolases
Hydrolysis reactions are catalyzed by hydrolases. These are enzymes that transfer functional groups to water.
Lyases
Lyases are enzymes that moves groups to double bonds or remove groups to form double bonds.
Isomerases
This type of enzyme produces isomeres of a molecule by moving groups of atoms within a molecule.
Ligases
Ligases are enzymes that catalyze condensation reactions during ATP cleavage to form bonds between a carbon atom and either another carbon atom, sulfur, oxygen, or nitrogen.
Reference:
Nelson, David L. Lehninger Principles of Biochemistry 4th ed. W.H. Freeman and Company. 2005