Protease

<p>Source:<a href="http://en.wikipedia.org/wiki/Protease">http://en.wikipedia.org/wiki/Protease</a></p>

<p>

A <b>protease</b> (also termed <b>peptidase</b> or <b>proteinase</b>) is any <a href="http://en.wikipedia.org/wiki/Enzyme" title="Enzyme" >enzyme</a> that conducts <a href="http://en.wikipedia.org/wiki/Proteolysis" title="Proteolysis" >proteolysis</a>, that is, begins <a href="http://en.wikipedia.org/wiki/Protein" title="Protein" >protein</a> <a href="http://en.wikipedia.org/wiki/Catabolism" title="Catabolism" >catabolism</a> by <a href="http://en.wikipedia.org/wiki/Hydrolysis" title="Hydrolysis" >hydrolysis</a>of the <a href="http://en.wikipedia.org/wiki/Peptide_bond" title="Peptide bond" >peptide bonds</a> that link <a href="http://en.wikipedia.org/wiki/Amino_acid" title="Amino acid" >amino acids</a> together in the <a href="http://en.wikipedia.org/wiki/Polypeptide" title="Polypeptide" class="mw-redirect" >polypeptide</a> chain forming the protein.</p>

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<h2 >Contents</h2>

  [<a href="http://en.wikipedia.org/wiki/Protease#" class="internal" id="togglelink" >hide</a>] </div>

<ul >

<li class="toclevel-1 tocsection-1" ><a href="http://en.wikipedia.org/wiki/Protease#Classification" >1 Classification</a>

<ul >

<li class="toclevel-2 tocsection-2" ><a href="http://en.wikipedia.org/wiki/Protease#Standard" >1.1 Standard</a></li>

<li class="toclevel-2 tocsection-3" ><a href="http://en.wikipedia.org/wiki/Protease#By_optimal_pH" >1.2 By optimal pH</a></li>

</ul>

</li>

<li class="toclevel-1 tocsection-4" ><a href="http://en.wikipedia.org/wiki/Protease#Occurrence" >2 Occurrence</a></li>

<li class="toclevel-1 tocsection-5" ><a href="http://en.wikipedia.org/wiki/Protease#Inhibitors" >3 Inhibitors</a></li>

<li class="toclevel-1 tocsection-6" ><a href="http://en.wikipedia.org/wiki/Protease#Degradation" >4 Degradation</a></li>

<li class="toclevel-1 tocsection-7" ><a href="http://en.wikipedia.org/wiki/Protease#Protease_research" >5 Protease research</a></li>

<li class="toclevel-1 tocsection-9" ><a href="http://en.wikipedia.org/wiki/Protease#Notes" >7 Notes</a></li>

<li class="toclevel-1 tocsection-10" ><a href="http://en.wikipedia.org/wiki/Protease#References" >8 References</a></li>

<li class="toclevel-1 tocsection-11" ><a href="http://en.wikipedia.org/wiki/Protease#External_links" >9 External links</a></li>

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<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=1" title="Edit section: Classification" >edit</a>]Classification</h2>

<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=2" title="Edit section: Standard" >edit</a>]Standard</h3>

<p >Proteases are currently classified into six broad groups:</p>

<ul >

<li ><a href="http://en.wikipedia.org/wiki/Serine_protease" title="Serine protease" >Serine proteases</a></li>

<li ><a href="http://en.wikipedia.org/wiki/Threonine_protease" title="Threonine protease" >Threonine proteases</a></li>

<li ><a href="http://en.wikipedia.org/wiki/Cysteine_protease" title="Cysteine protease" >Cysteine proteases</a></li>

<li ><a href="http://en.wikipedia.org/wiki/Aspartate_protease" title="Aspartate protease" >Aspartate proteases</a></li>

<li ><a href="http://en.wikipedia.org/wiki/Metalloprotease" title="Metalloprotease" class="mw-redirect" >Metalloproteases</a></li>

<li ><a href="http://en.wikipedia.org/w/index.php?title=Glutamic_acid_protease&action=edit&redlink=1" class="new" title="Glutamic acid protease (page does not exist)" >Glutamic acid proteases</a></li>

</ul>

<p >The <a href="http://en.wikipedia.org/wiki/Threonine" title="Threonine" >threonine</a> and <a href="http://en.wikipedia.org/wiki/Glutamic_acid" title="Glutamic acid" >glutamic-acid</a> proteases were not described until 1995 and 2004, respectively. The mechanism used to cleave a <a href="http://en.wikipedia.org/wiki/Peptide_bond" title="Peptide bond" >peptide bond</a>involves making an amino acid residue that has the <a href="http://en.wikipedia.org/wiki/Cysteine" title="Cysteine" >cysteine</a> and threonine (proteases) or a water molecule (<a href="http://en.wikipedia.org/wiki/Aspartic_acid" title="Aspartic acid" >aspartic acid</a>, metallo- and glutamic acid proteases) nucleophilic so that it can attack the peptide <a href="http://en.wikipedia.org/wiki/Carboxyl" title="Carboxyl" class="mw-redirect" >carboxyl</a> group. One way to make a nucleophile is by a <a href="http://en.wikipedia.org/wiki/Catalytic_triad" title="Catalytic triad" >catalytic triad</a>, where a<a href="http://en.wikipedia.org/wiki/Histidine" title="Histidine" >histidine</a> residue is used to activate <a href="http://en.wikipedia.org/wiki/Serine" title="Serine" >serine</a>, <a href="http://en.wikipedia.org/wiki/Cysteine" title="Cysteine" >cysteine</a>, or <a href="http://en.wikipedia.org/wiki/Threonine" title="Threonine" >threonine</a> as a nucleophile.

Within each of the broad groups proteases have been classified, by Rawlings and Barrett, into families of related proteases. For example within the <a href="http://en.wikipedia.org/wiki/Serine" title="Serine" >serine</a> proteases families are labelled Sx where S denotes the serine catalytic type and the x denotes the number of the family, for example S1 (<a href="http://en.wikipedia.org/wiki/Chymotrypsin" title="Chymotrypsin" >chymotrypsins</a>). An up to date classification of proteases into families is found in the MEROPS database.<sup id="cite_ref-pmid19892822_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Protease#cite_note-pmid19892822-0" >[1]</a></sup><sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Protease#cite_note-1" >[2]</a></sup></p>

<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=3" title="Edit section: By optimal pH" >edit</a>]By optimal pH</h3>

<p >Alternatively, proteases may be classified by the optimal <a href="http://en.wikipedia.org/wiki/PH" title="PH" >pH</a> in which they are active:</p>

<ul >

<li ><i>Acid proteases</i></li>

<li ><i>Neutral proteases</i> involved in <a href="http://en.wikipedia.org/wiki/Type_1_hypersensitivity" title="Type 1 hypersensitivity" class="mw-redirect" >type 1 hypersensitivity</a>. Here, it is released by <a href="http://en.wikipedia.org/wiki/Mast_cell" title="Mast cell" >mast cells</a> and causes activation of <a href="http://en.wikipedia.org/wiki/Complement_system" title="Complement system" >complement</a> and <a href="http://en.wikipedia.org/wiki/Kinins" title="Kinins" class="mw-redirect" >kinins</a>.<sup id="cite_ref-Kumar122_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Protease#cite_note-Kumar122-2" >[3]</a></sup>This group includes the <a href="http://en.wikipedia.org/wiki/Calpains" title="Calpains" class="mw-redirect" >calpains</a>.</li>

<li ><i>Basic proteases</i> (or <i>alkaline proteases</i>)</li>

</ul>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=4" title="Edit section: Occurrence" >edit</a>]Occurrence</h2>

<p >Proteases occur naturally in all organisms. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated cascades (e.g., the <a href="http://en.wikipedia.org/wiki/Coagulation" title="Coagulation" >blood-clotting cascade</a>, the <a href="http://en.wikipedia.org/wiki/Complement_system" title="Complement system" >complement system</a>, <a href="http://en.wikipedia.org/wiki/Apoptosis" title="Apoptosis" >apoptosis</a> pathways, and the invertebrate prophenoloxidase-activating cascade). Proteases can either break specific peptide bonds (<i>limited proteolysis</i>), depending on the <a href="http://en.wikipedia.org/wiki/Amino_acid" title="Amino acid" >amino acid</a>sequence of a protein, or break down a complete peptide to amino acids (<i>unlimited proteolysis</i>). The activity can be a destructive change, abolishing a protein's function or digesting it to its principal components; it can be an activation of a function, or it can be a signal in a signaling pathway.

Bacteria also secrete proteases to <a href="http://en.wikipedia.org/wiki/Hydrolyse" title="Hydrolyse" class="mw-redirect" >hydrolyse</a> (digest) the peptide bonds in proteins and therefore break the proteins down into their constituent<a href="http://en.wikipedia.org/wiki/Monomer" title="Monomer" >monomers</a>. Bacterial and fungal proteases are particularly important to the global <a href="http://en.wikipedia.org/wiki/Carbon" title="Carbon" >carbon</a> and <a href="http://en.wikipedia.org/wiki/Nitrogen" title="Nitrogen" >nitrogen</a> cycles in the recycling of proteins, and such activity tends to be regulated in by nutritional signals in these organisms.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Protease#cite_note-3" >[4]</a></sup> The net impact of nutritional regulation of protease activity among the thousands of species present in soil can be observed at the overall microbial community level as proteins are broken down in response to carbon, nitrogen, or sulfur limitation.<sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Protease#cite_note-4" >[5]</a></sup>

A secreted bacterial protease may also act as an exotoxin, and be an example of a <a href="http://en.wikipedia.org/wiki/Virulence_factor" title="Virulence factor" >virulence factor</a> in bacterial <a href="http://en.wikipedia.org/wiki/Pathogenesis" title="Pathogenesis" >pathogenesis</a>. Bacterial exotoxic proteases destroy extracellular structures. Protease enzymes are also used extensively in the bread industry in <a href="http://en.wikipedia.org/wiki/Bread_improver" title="Bread improver" >bread improver</a>.

Proteases, also known as proteinases or proteolytic enzymes, are a large group of <a href="http://en.wikipedia.org/wiki/Enzymes" title="Enzymes" class="mw-redirect" >enzymes</a>. Proteases belong to the class of enzymes known as <a href="http://en.wikipedia.org/wiki/Hydrolases" title="Hydrolases" class="mw-redirect" >hydrolases</a>, which catalyse the reaction of <a href="http://en.wikipedia.org/wiki/Hydrolysis" title="Hydrolysis" >hydrolysis</a> of various bonds with the participation of a water molecule.

Proteases are involved in digesting long protein chains into short fragments, splitting the <a href="http://en.wikipedia.org/wiki/Peptide_bonds" title="Peptide bonds" class="mw-redirect" >peptide bonds</a> that link <a href="http://en.wikipedia.org/wiki/Amino_acid" title="Amino acid" >amino acid</a> residues. Some of them can detach the terminal amino acids from the protein chain (<a href="http://en.wikipedia.org/wiki/Exopeptidases" title="Exopeptidases" class="mw-redirect" >exopeptidases</a>, such as <a href="http://en.wikipedia.org/wiki/Aminopeptidase" title="Aminopeptidase" >aminopeptidases</a>, <a href="http://en.wikipedia.org/wiki/Carboxypeptidase_A" title="Carboxypeptidase A" >carboxypeptidase A</a>); the others attack internal peptide bonds of a protein (<a href="http://en.wikipedia.org/wiki/Endopeptidases" title="Endopeptidases" class="mw-redirect" >endopeptidases</a>, such as <a href="http://en.wikipedia.org/wiki/Trypsin" title="Trypsin" >trypsin</a>, <a href="http://en.wikipedia.org/wiki/Chymotrypsin" title="Chymotrypsin" >chymotrypsin</a>, <a href="http://en.wikipedia.org/wiki/Pepsin" title="Pepsin" >pepsin</a>, <a href="http://en.wikipedia.org/wiki/Papain" title="Papain" >papain</a>, <a href="http://en.wikipedia.org/wiki/Elastase" title="Elastase" >elastase</a>).

Proteases are divided into four major groups according to the character of their catalytic <a href="http://en.wikipedia.org/wiki/Active_site" title="Active site" >active site</a> and conditions of action: serine proteinases, cysteine (thiol) proteinases, aspartic proteinases, and <a href="http://en.wikipedia.org/wiki/Metalloproteinase" title="Metalloproteinase" >metalloproteinases</a>. Attachment of a protease to a certain group depends on the structure of catalytic site and the amino acid (as one of the constituents) essential for its activity.

Proteases are used throughout an organism for various metabolic processes. Acid proteases secreted into the stomach (such as <a href="http://en.wikipedia.org/wiki/Pepsin" title="Pepsin" >pepsin</a>) and serine proteases present in <a href="http://en.wikipedia.org/wiki/Duodenum" title="Duodenum" >duodenum</a> (<a href="http://en.wikipedia.org/wiki/Trypsin" title="Trypsin" >trypsin</a> and <a href="http://en.wikipedia.org/wiki/Chymotrypsin" title="Chymotrypsin" >chymotrypsin</a>) enable us to digest the protein in food; proteases present in blood serum (<a href="http://en.wikipedia.org/wiki/Thrombin" title="Thrombin" >thrombin</a>, <a href="http://en.wikipedia.org/wiki/Plasmin" title="Plasmin" >plasmin</a>, <a href="http://en.wikipedia.org/wiki/Hageman_factor" title="Hageman factor" class="mw-redirect" >Hageman factor</a>, etc.) play important role in blood-clotting, as well as lysis of the clots, and the correct action of the immune system. Other proteases are present in leukocytes (<a href="http://en.wikipedia.org/wiki/Elastase" title="Elastase" >elastase</a>, <a href="http://en.wikipedia.org/wiki/Cathepsin_G" title="Cathepsin G" >cathepsin G</a>) and play several different roles in metabolic control. Proteases determine the lifetime of other proteins playing important physiological role like hormones, antibodies, or other enzymes—this is one of the fastest "switching on" and "switching off" regulatory mechanisms in the physiology of an organism. By complex cooperative action the proteases may proceed as <a href="http://en.wikipedia.org/w/index.php?title=Biochemical_cascades&action=edit&redlink=1" class="new" title="Biochemical cascades (page does not exist)" >cascade</a> reactions, which result in rapid and efficient amplification of an organism's response to a physiological signal.

Proteases are part of many <a href="http://en.wikipedia.org/wiki/Laundry_detergent" title="Laundry detergent" >laundry detergents</a>.</p>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=5" title="Edit section: Inhibitors" >edit</a>]Inhibitors</h2>

<p >The activity of proteases is inhibited by <a href="http://en.wikipedia.org/wiki/Protease_inhibitor_(biology)" title="Protease inhibitor (biology)" >protease inhibitors</a>. One example of protease inhibitors is the <a href="http://en.wikipedia.org/wiki/Serpin" title="Serpin" >serpin</a> superfamily, which includes <a href="http://en.wikipedia.org/wiki/Alpha_1-antitrypsin" title="Alpha 1-antitrypsin" >alpha 1-antitrypsin</a>, <a href="http://en.wikipedia.org/wiki/C1-inhibitor" title="C1-inhibitor" >C1-inhibitor</a>, <a href="http://en.wikipedia.org/wiki/Antithrombin" title="Antithrombin" >antithrombin</a>, <a href="http://en.wikipedia.org/wiki/Alpha_1-antichymotrypsin" title="Alpha 1-antichymotrypsin" >alpha 1-antichymotrypsin</a>, <a href="http://en.wikipedia.org/wiki/Plasminogen_activator_inhibitor_1" title="Plasminogen activator inhibitor 1" class="mw-redirect" >plasminogen activator inhibitor-1</a>, and <a href="http://en.wikipedia.org/wiki/Neuroserpin" title="Neuroserpin" class="mw-redirect" >neuroserpin</a>.

Natural protease inhibitors include the family of <a href="http://en.wikipedia.org/wiki/Lipocalin" title="Lipocalin" >lipocalin</a> proteins, which play a role in cell regulation and differentiation. <a href="http://en.wikipedia.org/wiki/Lipophilic" title="Lipophilic" class="mw-redirect" >Lipophilic</a> ligands, attached to lipocalin proteins, have been found to possess tumor protease inhibiting properties. The natural <a href="http://en.wikipedia.org/wiki/Protease_inhibitor(biology)" title="Protease inhibitor (biology)" >protease inhibitors</a> are not to be confused with the <a href="http://en.wikipedia.org/wiki/Protease_inhibitor(pharmacology)" title="Protease inhibitor (pharmacology)" >protease inhibitors</a> used in antiretroviral therapy. Some <a href="http://en.wikipedia.org/wiki/Virus(biology)" title="Virus (biology)" class="mw-redirect" >viruses</a>, with <a href="http://en.wikipedia.org/wiki/HIV/AIDS" title="HIV/AIDS" class="mw-redirect" >HIV/AIDS</a> among them, depend on proteases in their reproductive cycle. Thus, <a href="http://en.wikipedia.org/wiki/Protease_inhibitor(pharmacology)" title="Protease inhibitor (pharmacology)" >protease inhibitors</a> are developed as <a href="http://en.wikipedia.org/wiki/Antiviral_drug" title="Antiviral drug" >antiviral</a> means.</p>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=6" title="Edit section: Degradation" >edit</a>]Degradation</h2>

<p >Proteases, being themselves proteins, are known to be cleaved by other protease molecules, sometimes of the same variety. This may be an important method of regulation of protease activity.</p>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=7" title="Edit section: Protease research" >edit</a>]Protease research</h2>

<p >The field of protease research is enormous. Barrett and Rawlings estimated that approximately 8001 papers related to this field are published each year. For a look at current activities and interests of protease researchers, see the <a rel="nofollow" class="external text" href="http://www.protease.org/" >International Proteolysis Society</a> web page.</p>

<ul >

<li ><a href="http://en.wikipedia.org/wiki/The_Proteolysis_Map" title="The Proteolysis Map" >The Proteolysis Map</a></li>

<li ><a href="http://en.wikipedia.org/wiki/TopFIND" title="TopFIND" >TopFIND</a>, a scientific database covering proteases, their cleavage site specificity, substrates, inhibitors and protein termini originating from their activity</li>

<li ><a href="http://en.wikipedia.org/wiki/David_Ho_(scientist)" title="David Ho (scientist)" >David Ho</a>, an AIDS researcher famous for pioneering the use of protease inhibitors in treating HIV-infected patients</li>

<li ><a href="http://en.wikipedia.org/wiki/Proteases_in_angiogenesis" title="Proteases in angiogenesis" >Proteases in angiogenesis</a></li>

</ul>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=9" title="Edit section: Notes" >edit</a>]Notes</h2>

<li id="cite_note-pmid19892822-0" ><b><a href="http://en.wikipedia.org/wiki/Protease#cite_ref-pmid19892822_0-0" >^{</a></b>&nbsp};Rawlings ND, Barrett AJ, Bateman A (January 2010). <a rel="nofollow" class="external text" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2808883" >"MEROPS: the peptidase database"</a>. <i>Nucleic Acids Res.</i> <b>38</b> (Database issue): D227–33.<a href="http://en.wikipedia.org/wiki/Digital_object_identifier" title="Digital object identifier" >doi</a>:<a rel="nofollow" class="external text" href="http://dx.doi.org/10.1093%2Fnar%2Fgkp971" >10.1093/nar/gkp971</a>. <a href="http://en.wikipedia.org/wiki/PubMed_Central" title="PubMed Central" >PMC</a> <a rel="nofollow" class="external text" href="http://www.pubmedcentral.gov/articlerender.fcgi?tool=pmcentrez&artid=2808883" >2808883</a>. <a href="http://en.wikipedia.org/wiki/PubMed_Identifier" title="PubMed Identifier" class="mw-redirect" >PMID</a> <a rel="nofollow" class="external text" href="http://www.ncbi.nlm.nih.gov/pubmed/19892822" >19892822</a>.</li>

<li id="cite_note-1" ><b><a href="http://en.wikipedia.org/wiki/Protease#cite_ref-1" >^{</a></b> }<a rel="nofollow" class="external text" href="http://merops.sanger.ac.uk/" >MEROPS</a></li>

<li id="cite_note-Kumar122-2" ><b><a href="http://en.wikipedia.org/wiki/Protease#cite_ref-Kumar122_2-0" >^{</a></b> Mitchell}, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson (2007). <i>Robbins Basic Pathology</i>. Philadelphia: Saunders. pp. 122.<a href="http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number" >ISBN</a> <a href="http://en.wikipedia.org/wiki/Special:BookSources/1-4160-2973-7" title="Special:BookSources/1-4160-2973-7" >1-4160-2973-7</a>. 8th edition.</li>

<li id="cite_note-3" ><b><a href="http://en.wikipedia.org/wiki/Protease#cite_ref-3" >^{</a></b> Sims}, G.K. 2006. Nitrogen Starvation Promotes Biodegradation of N-Heterocyclic Compounds in Soil. Soil Biology & Biochemistry 38:2478-2480.</li>

<li id="cite_note-4" ><b><a href="http://en.wikipedia.org/wiki/Protease#cite_ref-4" >^{</a></b> Sims}, G. K., and M. M. Wander. 2002. Proteolytic activity under nitrogen or sulfur limitation. Appl. Soil Ecol. 568:1-5.</li>

</ol>

</div>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=10" title="Edit section: References" >edit</a>]References</h2>

<ul >

<li >Barrett A.J., Rawlings ND, Woessner JF. <i>The Handbook of Proteolytic Enzymes</i>, 2nd ed. Academic Press, 2003. <a href="http://en.wikipedia.org/wiki/Special:BookSources/0120796104" class="internal mw-magiclink-isbn" >ISBN 0-12-079610-4</a>.</li>

<li >Hedstrom L. <i>Serine Protease Mechanism and Specificity.</i> Chem Rev 2002;102:4501-4523.</li>

<li >Southan C. <i>A genomic perspective on human proteases as drug targets.</i> Drug Discov Today 2001;6:681-688.</li>

<li >Hooper NM. <i>Proteases in Biology and Medicine</i>. London: Portland Press, 2002. <a href="http://en.wikipedia.org/wiki/Special:BookSources/1855781476" class="internal mw-magiclink-isbn" >ISBN 1-85578-147-6</a>.</li>

<li >Puente XS, Sanchez LM, Overall CM, Lopez-Otin C. <i>Human and Mouse Proteases: a Comparative Genomic Approach.</i> Nat Rev Genet 2003;4:544-558.</li>

<li >Ross J, Jiang H, Kanost MR, Wang Y. <i>Serine proteases and their homologs in the Drosophila melanogaster genome: an initial analysis of sequence conservation and phylogenetic relationships.</i> Gene 2003;304:117-31.</li>

<li >Puente XS, Lopez-Otin C. <i>A Genomic Analysis of Rat Proteases and Protease Inhibitors.</i> Genome Biol 2004;14:609-622.</li>

<li >Lucía Feijoo-Siota, Tomás G. Villa <i>Native and Biotechnologically Engineered Plant Proteases with Industrial Applications.</i> Food and Bioprocess Technology 2010.</li>

</ul>

</div>

<h2 >[<a href="http://en.wikipedia.org/w/index.php?title=Protease&action=edit&section=11" title="Edit section: External links" >edit</a>]External links</h2>

<ul >

<li ><a rel="nofollow" class="external text" href="http://www.protease.org/" >International Proteolysis Society</a></li>

<li ><a rel="nofollow" class="external text" href="http://merops.sanger.ac.uk/" >Merops - the peptidase database</a></li>

<li ><a rel="nofollow" class="external text" href="http://www.sciencegateway.org/resources/protease.htm" >List of protease inhibitors</a></li>

<li ><a rel="nofollow" class="external text" href="http://www.expasy.org/tools/peptidecutter/" >Protease cutting predictor</a></li>

<li ><a rel="nofollow" class="external text" href="http://www.expasy.org/tools/peptidecutter/peptidecutter_enzymes.html" >List of proteases and their specificities</a> (see also <a rel="nofollow" class="external autonumber" href="http://www.expasy.org/cgi-bin/lists?peptidas.txt" >[1]</a>)</li>

<li ><a rel="nofollow" class="external text" href="http://www.proteolysis.org/" >Proteolysis MAP from Center for Proteolytic Pathways</a></li>

<li ><a rel="nofollow" class="external text" href="http://cutdb.burnham.org/" >Proteolysis Cut Site database - curated expert annotation from users</a></li>

<li ><a rel="nofollow" class="external text" href="http://substrate.burnham.org/" >Protease cut sites graphical interface</a></li>

<li ><a rel="nofollow" class="external text" href="http://clipserve.clip.ubc.ca/topfind" >TopFIND protease database covering cut sites, substrates and protein termini</a></li>

<li ><a href="http://en.wikipedia.org/wiki/Medical_Subject_Headings" title="Medical Subject Headings" >MeSH</a> <i><a rel="nofollow" class="external text" href="http://www.nlm.nih.gov/cgi/mesh/2011/MB_cgi?mode=&term=Proteases" >Proteases</a></i></li>

</ul>