Editing Active site (section)

{{Short description|Active region of an enzyme}}
[[File:Enzyme structure.svg|thumb|400px|alt=Lysozyme displayed as an opaque globular surface with a pronounced cleft which the substrate depicted as a stick diagram snuggly fits into.|Organisation of [[protein structure|enzyme structure]] and [[lysozyme]] example. Binding sites in blue, catalytic site in red and [[peptidoglycan]] substrate in black. ({{PDB|9LYZ}})]]

In [[biology]] and [[biochemistry]], the '''active site''' is the region of an [[enzyme]] where [[substrate (biochemistry)|substrate]] molecules bind and undergo a chemical reaction. The active site consists of [[amino acid]] residues that form temporary bonds with the substrate, the ''[[binding site]]'', and residues that [[enzyme catalysis|catalyse]] a reaction of that substrate, the '''''catalytic site'''''. Although the active site occupies only ~10–20% of the volume of an enzyme,<ref name=":0">{{Cite book |url=http://fcebichivirtuallibrary.info/ebooks/Chem/Introduction_To_Enzyme_And_Coenzyme_Chemistry.pdf |title=Introduction to Enzyme and Coenzyme Chemistry |vauthors=Bugg TD |publisher=Blackwell Publishing Limited |year=2004 |isbn=9781405114523 |edition=2nd |archive-url=https://web.archive.org/web/20180322143320/http://fcebichivirtuallibrary.info/ebooks/Chem/Introduction_To_Enzyme_And_Coenzyme_Chemistry.pdf |archive-date=22 March 2018 |url-status=dead}}</ref>{{Rp|19}} it is the most important part as it directly catalyzes the [[chemical reaction]]. It usually consists of three to four amino acids, while other amino acids within the protein are required to maintain the [[tertiary structure]] of the enzymes.<ref name="google48">{{Cite book|url=https://books.google.com/books?id=KrGn_obcy6QC&pg=PA48|title=Enzyme Technology|vauthors=Shanmugam S|publisher=I K International Publishing House|year=2009|isbn=9789380026053|pages=48}}</ref>

Each active site is evolved to be optimised to bind a particular substrate and catalyse a particular reaction, resulting in high [[chemical specificity|specificity]]. This specificity is determined by the arrangement of amino acids within the active site and the structure of the substrates. Sometimes enzymes also need to bind with some [[cofactor (biochemistry)|cofactor]]s to fulfil their function. The active site is usually a groove or pocket of the enzyme which can be located in a deep tunnel within the enzyme,<ref name="Pravda">{{cite journal |display-authors=3 |vauthors=Pravda L, Berka K, Svobodová Vařeková R, Sehnal D, Banáš P, Laskowski RA, Koča J, Otyepka M |date=2014 |title=Anatomy of Enzyme Channels |journal=[[BMC Bioinformatics]] |volume=15 |issue=1 |pages=379 |doi=10.1186/s12859-014-0379-x |pmc=4245731 |pmid=25403510 |doi-access=free }}</ref> or between the interfaces of [[Protein quaternary structure|multimeric enzymes]]. An active site can catalyse a reaction repeatedly as residues are not altered at the end of the reaction (they may change during the reaction, but are regenerated by the end).<ref>{{Cite book |url=https://books.google.com/books?id=xg0vAQAAIAAJ |title=Essential Cell Biology |vauthors=Alberts B |publisher=Garland Science |year=2010 |isbn=9780815341291 |pages=91}}</ref> This process is achieved by lowering the [[activation energy]] of the reaction, so more substrates have enough energy to undergo reaction.