A protease (or proteinase) breaks down proteins. A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein. Proteases work best in acidic conditions. Classification Standard Proteases are classified into six groups: Serine proteases Threonine proteases Cysteine proteases Aspartate proteases Metalloproteases Glutamic acid proteases The threonine and glutamic… (More on Protease)