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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 inhibitors are
not to be confused with the protease inhibitors used in antiretroviral therapy. Some viruses, with HIV among them, depend
on proteases in their reproductive cycle. Thus, protease inhibitors are developed as antiviral means.
As peptidases are themselves peptides, one natually wonders if they degrade themselves. In fact, many peptidases to cleave
themselves. This may be an important method of regulation of peptidase activity.
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