How many classes of enzymes are there?

There are a total of 7 classes of enzymes which are: hydrolases, lyases, isomerases, ligases, translocases, transferases, and oxidoreductases. 

1. Oxidoreductases form a class of enzymes specifically involved in catalyzing oxidoreduction reactions. These enzymes facilitate the transfer of electrons from one molecule to another molecule]. 
2. Hydrolases are a group of enzymes known for their ability to catalyze hydrolytic reactions, which involve breaking down substrates with the assistance of water. These enzymes utilize water molecules to donate hydroxyl groups during the process of substrate degradation. 
3. Lyases are a class of enzymes that facilitate chemical reactions involving the addition or removal of specific elements at double bonds within molecules. 
4. Isomerases are a class of enzymes which accelerates chemical reactions where the molecules undergo rearrangements in their structure. 
5. Ligases, which are about 50 in number,  facilitate reactions that preserve chemical energy and establish a link between energy-consuming synthetic processes and energy-releasing breakdown reactions. They achieve this by catalyzing the joining of two molecules, utilizing the energy released from breaking an energy-rich phosphate bond. This involves the conversion of ATP into ADP while simultaneously harnessing the released energy for cellular processes. 
6. A translocase is a protein primarily involved in aiding the movement of molecules, typically across a cell membrane. 
7. Transferases are a category of enzymes that facilitate the transfer of specific functional groups from one molecule to another.