How many types of proteases are there?

Proteases catalyze the proteolysis through different mechanisms, which can be classified into 6 main groups based on the different active site residues they employ to perform catalysis.

• Serine proteases: using the serine residue.
• Cysteine proteases: using a cysteine thiol.
• Threonine proteases: using the secondary alcohol of N-terminal threonine.
• Aspartic proteases: using the carboxylic acid of aspartate residue.
• Glutamic proteases: using the carboxylic acid of glutamate residue.
• Metalloproteases: using a metal, such as zinc and cobalt, to perform catalysis.