1. Oxidoreductases. To this class belong all enzymes catalysing oxidoreduction reactions.
2. Transferases. Transferases are enzymes transferring a groupfrom one compound to another compound
3. Hydrolases. These enzymes catalyse the hydrolytic cleavage of C-O, C-N, C-C and some other bonds
4. Lyases. Lyases are enzymes cleaving C-C, C-O, C-N, and other bonds by elimination, leaving double bonds or rings, or conversely adding groups to double bonds.
5. Isomerases. These enzymes catalyse geometric or structural changes within one molecule.
6. Ligases. Ligases are enzymes catalysing the joining together of two molecules coupled with the hydrolysis of a diphosphate bond in ATP or a similar triphosphate.