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<p>The <strong>Enzyme Commission number</strong> (<strong>EC number</strong>) is a numerical classification scheme for <font color="#810081">enzymes</font>, based on the chemical reactions they catalyze. As a system of <strong>enzyme nomenclature</strong>, every EC number is associated with a recommended name for the respective enzyme.</p>
<p>Strictly speaking, EC numbers do not specify enzymes, but enzyme-catalyzed reactions. If different enzymes (for instance from different organisms) catalyze the same reaction, then they receive the same EC number. By contrast, UniProt identifiers uniquely specify a protein by its amino acid sequence.<sup class="reference" id="_ref-0">[1]</sup></p>
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<h2><span class="mw-headline">Format of number</span></h2>
<p>Every enzyme code consists of the letters "EC" followed by four numbers separated by periods. Those numbers represent a progressively finer classification of the enzyme.</p>
<p>For example, the tripeptide aminopeptidases have the code "EC 3.4.11.4", whose components indicate the following groups of enzymes:</p>
<ul>
<li><em>EC 3</em> enzymes are hydrolases (enzymes that use water to break up some other molecule) </li>
<li><em>EC 3.4</em> are hydrolases that act on peptide bonds </li>
<li><em>EC 3.4.11</em> are those hydrolases that cleave off the amino-terminal amino acid from a polypeptide </li>
<li><em>EC 3.4.11.4</em> are those that cleave off the amino-terminal end from a tripeptide </li>
</ul>
<p> </p>
<h2><span class="mw-headline">Top level codes</span></h2>
<table class="wikitable">
<caption>Top-level EC numbers<sup class="reference" id="_ref-1">[2]</sup></caption>
<tbody>
<tr>
<th>Group</th>
<th>Reaction catalyzed</th>
<th>Typical reaction</th>
<th>Enzyme example(s) with trivial name</th>
</tr>
<tr>
<th>EC 1<br />
<em>Oxidoreductases</em></th>
<td>To catalyze oxidation/reduction reactions; transfer of H and O atoms or electrons from one substance to another</td>
<td>AH + B → A + BH (<small><strong><font size="2">reduced</font></strong></small>)<br />
A + O → AO (<small><strong><font size="2">oxidized</font></strong></small>)</td>
<td>Dehydrogenase, oxidase</td>
</tr>
<tr>
<th>EC 2<br />
<em>Transferases</em></th>
<td>Transfer of a functional group from one substance to another. The group may be methyl-, acyl-, amino- or phosphate group</td>
<td>AB + C → A + BC</td>
<td>Transaminase, kinase</td>
</tr>
<tr>
<th>EC 3<br />
<em>Hydrolases</em></th>
<td>Formation of two products from a substrate by hydrolysis</td>
<td>AB + H<sub>2</sub>O → AOH + BH</td>
<td>Lipase, amylase, peptidase</td>
</tr>
<tr>
<th>EC 4<br />
<em>Lyases</em></th>
<td>Non-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved</td>
<td>RCOCOOH → RCOH + CO<sub>2</sub></td>
<td> </td>
</tr>
<tr>
<th>EC 5<br />
<em>Isomerases</em></th>
<td>Intramolecule rearrangement, i.e. isomerization changes within a single molecule</td>
<td>AB → BA</td>
<td>Isomerase, mutase</td>
</tr>
<tr>
<th>EC 6<br />
<em>Ligases</em></th>
<td>Join together two molecules by synthesis of new C-O, C-S, C-N or C-C bonds with simultaneous breakdown of ATP</td>
<td>X + Y+ ATP → XY + ADP + Pi</td>
<td>Synthetase</td>
</tr>
</tbody>
</table>
<p> </p>
<h2><span class="mw-headline">History</span></h2>
<p>The enzyme nomenclature scheme was developed starting in 1955, when the International Congress of Biochemistry in Brussels set up an Enzyme Commission.</p>
<p>The first version was published in 1961.</p>
<p>The current sixth edition, published by the International Union of Biochemistry and Molecular Biology in 1992, contains 3196 different enzymes.</p>
<p> </p>
<h2><span class="mw-headline">References</span></h2>
<ol class="references">
<li id="_note-0"><strong>^</strong> ENZYME (Enzyme nomenclature database). ExPASy. Retrieved on 2006-03-14. </li>
<li id="_note-1"><strong>^</strong> Moss, G.P.. Recommendations of the Nomenclature Committee. International Union of Biochemistry and Molecular Biology on the Nomenclature and Classification of Enzymes by the Reactions they Catalyse. Retrieved on 2006-03-14. </li>
</ol>
<p> </p>
<h2><span class="mw-headline">See also</span></h2>
<ul>
<li><a title="TC number" href="http://en.wikipedia.org/wiki/TC_number">TC number</a> (classification of membrane transport proteins) </li>
<li><a title="List of enzymes" href="http://en.wikipedia.org/wiki/List_of_enzymes">List of enzymes</a> </li>
</ul>
<p>Strictly speaking, EC numbers do not specify enzymes, but enzyme-catalyzed reactions. If different enzymes (for instance from different organisms) catalyze the same reaction, then they receive the same EC number. By contrast, UniProt identifiers uniquely specify a protein by its amino acid sequence.<sup class="reference" id="_ref-0">[1]</sup></p>
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if (window.showTocToggle) { var tocShowText = "show"; var tocHideText = "hide"; showTocToggle(); }
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<p> </p>
<h2><span class="mw-headline">Format of number</span></h2>
<p>Every enzyme code consists of the letters "EC" followed by four numbers separated by periods. Those numbers represent a progressively finer classification of the enzyme.</p>
<p>For example, the tripeptide aminopeptidases have the code "EC 3.4.11.4", whose components indicate the following groups of enzymes:</p>
<ul>
<li><em>EC 3</em> enzymes are hydrolases (enzymes that use water to break up some other molecule) </li>
<li><em>EC 3.4</em> are hydrolases that act on peptide bonds </li>
<li><em>EC 3.4.11</em> are those hydrolases that cleave off the amino-terminal amino acid from a polypeptide </li>
<li><em>EC 3.4.11.4</em> are those that cleave off the amino-terminal end from a tripeptide </li>
</ul>
<p> </p>
<h2><span class="mw-headline">Top level codes</span></h2>
<table class="wikitable">
<caption>Top-level EC numbers<sup class="reference" id="_ref-1">[2]</sup></caption>
<tbody>
<tr>
<th>Group</th>
<th>Reaction catalyzed</th>
<th>Typical reaction</th>
<th>Enzyme example(s) with trivial name</th>
</tr>
<tr>
<th>EC 1<br />
<em>Oxidoreductases</em></th>
<td>To catalyze oxidation/reduction reactions; transfer of H and O atoms or electrons from one substance to another</td>
<td>AH + B → A + BH (<small><strong><font size="2">reduced</font></strong></small>)<br />
A + O → AO (<small><strong><font size="2">oxidized</font></strong></small>)</td>
<td>Dehydrogenase, oxidase</td>
</tr>
<tr>
<th>EC 2<br />
<em>Transferases</em></th>
<td>Transfer of a functional group from one substance to another. The group may be methyl-, acyl-, amino- or phosphate group</td>
<td>AB + C → A + BC</td>
<td>Transaminase, kinase</td>
</tr>
<tr>
<th>EC 3<br />
<em>Hydrolases</em></th>
<td>Formation of two products from a substrate by hydrolysis</td>
<td>AB + H<sub>2</sub>O → AOH + BH</td>
<td>Lipase, amylase, peptidase</td>
</tr>
<tr>
<th>EC 4<br />
<em>Lyases</em></th>
<td>Non-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved</td>
<td>RCOCOOH → RCOH + CO<sub>2</sub></td>
<td> </td>
</tr>
<tr>
<th>EC 5<br />
<em>Isomerases</em></th>
<td>Intramolecule rearrangement, i.e. isomerization changes within a single molecule</td>
<td>AB → BA</td>
<td>Isomerase, mutase</td>
</tr>
<tr>
<th>EC 6<br />
<em>Ligases</em></th>
<td>Join together two molecules by synthesis of new C-O, C-S, C-N or C-C bonds with simultaneous breakdown of ATP</td>
<td>X + Y+ ATP → XY + ADP + Pi</td>
<td>Synthetase</td>
</tr>
</tbody>
</table>
<p> </p>
<h2><span class="mw-headline">History</span></h2>
<p>The enzyme nomenclature scheme was developed starting in 1955, when the International Congress of Biochemistry in Brussels set up an Enzyme Commission.</p>
<p>The first version was published in 1961.</p>
<p>The current sixth edition, published by the International Union of Biochemistry and Molecular Biology in 1992, contains 3196 different enzymes.</p>
<p> </p>
<h2><span class="mw-headline">References</span></h2>
<ol class="references">
<li id="_note-0"><strong>^</strong> ENZYME (Enzyme nomenclature database). ExPASy. Retrieved on 2006-03-14. </li>
<li id="_note-1"><strong>^</strong> Moss, G.P.. Recommendations of the Nomenclature Committee. International Union of Biochemistry and Molecular Biology on the Nomenclature and Classification of Enzymes by the Reactions they Catalyse. Retrieved on 2006-03-14. </li>
</ol>
<p> </p>
<h2><span class="mw-headline">See also</span></h2>
<ul>
<li><a title="TC number" href="http://en.wikipedia.org/wiki/TC_number">TC number</a> (classification of membrane transport proteins) </li>
<li><a title="List of enzymes" href="http://en.wikipedia.org/wiki/List_of_enzymes">List of enzymes</a> </li>
</ul>
