Proteases are classified on the basis of catalytic mechanism, and seven known distinct classes are described: metallo, aspartic, cysteine, serine, glutamic, asparagine, and threonine.
Serine proteases - using a serine alcohol, display a wide range of functions.
Cysteine proteases - using a cysteine thiol, that include caspases which are involved in apoptosis and inflammation, and cathepsins which promote protein degradation.
Threonine proteases - using a threonine secondary alcohol
Aspartic proteases - using an aspartate carboxylic acid, that include beta and gamma secretases, the two enzymes necessary to release amyloid beta peptides from the Alzheimer's disease associated amyloid precursor protein (APP).
Glutamic proteases - using a glutamate carboxylic acid
Metalloproteases - using a metal, usually zinc. The Metalloprotease family includes aminopeptidases and endopeptidases, which are secreted, membrane-bound, or cytosolic.
Asparagine peptide lyases - using an asparagine to perform an elimination reaction (not requiring water)