Enzymes are classified into six types: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Enzyme classification is based upon the chemical reaction that the enzyme catalyzes.
Enzymes classified as oxidoreductases perform oxidation and reduction reactions, whereby one substrate is oxidized and another is reduced. Transferases move functional groups from one molecule to another. Hydrolases break single bonds between atoms by adding a water molecule. Lyases transfer amino groups, water or ammonia to form or remove a double bond within a molecule. Isomerases change the position of functional groups so that the substrate and product are isomers of one another, meaning that they contain the same number of atoms. Lastly, ligases catalyze chemical reactions through the removal of a water molecule to create single bonds.