Peptidase

Peptidases (old term: proteases, pronounced pro-tea-aces) are enzymes which break peptide bonds of proteins. They use a molecule of water to do so and are thus classified as hydrolases.

Peptidases occur naturally in living organisms, where they are used for molecular digestion and the breakdown of unwanted proteins. Peptidases can break either specific peptide bonds (limited proteolysis), depending on the amino acid sequence of a protein, or break down a complete peptide to amino acids (unlimited proteolysis).

The function of peptidases is inhibited by protease inhibitor enzymes. Examples of protease inhibitors are the class of serpins (serine protease or peptidase inhibitors), incorporating alpha 1-antitrypsin. Other serpins are complement 1-inhibitor, antithrombin, alpha 1-antichymotrypsin, plasminogen activator inhibitor 1 (coagulation, fibrinolysis) and the recently discovered neuroserpin.

The natural protease inhibitorss are not to be confused with the protease inhibitorss used in antiretroviral therapy. Some viruseses, with HIV among them, depend on proteases in their reproductive cycle. Thus, protease inhibitorss are developed as antiviral means.

As peptidases are themselves peptides, one natually wonders if they degrade themselves. In fact, many peptidases are known to cleave themselves. This may be an important method of regulation of peptidase activity.