Editing Enzyme (section)

== Structure ==
[[File:Q10 graph c.svg|thumb|400px|Enzyme activity initially increases with temperature ([[Q10 (temperature coefficient)|Q10 coefficient]]) until the enzyme's structure unfolds ([[denaturation (biochemistry)|denaturation]]), leading to an optimal [[rate of reaction]] at an intermediate temperature.|alt=A graph showing that reaction rate increases exponentially with temperature until denaturation causes it to decrease again.]]

{{see also|Protein structure}}

Enzymes are generally [[globular protein]]s, acting alone or in larger [[protein complex|complexes]]. The sequence of the amino acids specifies the structure which in turn determines the catalytic activity of the enzyme.<ref>{{cite journal | vauthors = Anfinsen CB | title = Principles that govern the folding of protein chains | journal = Science | volume = 181 | issue = 4096 | pages = 223–230 | date = July 1973 | pmid = 4124164 | doi = 10.1126/science.181.4096.223 | bibcode = 1973Sci...181..223A }}</ref> Although structure determines function, a novel enzymatic activity cannot yet be predicted from structure alone.<ref>{{cite journal | vauthors = Dunaway-Mariano D | title = Enzyme function discovery | journal = Structure | volume = 16 | issue = 11 | pages = 1599–1600 | date = November 2008 | pmid = 19000810 | doi = 10.1016/j.str.2008.10.001 | doi-access = free }}</ref> Enzyme structures unfold ([[denaturation (biochemistry)|denature]]) when heated or exposed to chemical denaturants and this disruption to the structure typically causes a loss of activity.<ref>{{cite book | vauthors = Petsko GA, Ringe D | title = Protein structure and function | date = 2003 | publisher = New Science | location = London | isbn=978-1405119221 | chapter = Chapter 1: From sequence to structure | chapter-url = https://books.google.com/books?id=2yRDWkHhN9QC&q=Protein+Denaturation+unfold+loss+of+function&pg=PA27 | page = 27 }}</ref> Enzyme denaturation is normally linked to temperatures above a species' normal level; as a result, enzymes from bacteria living in volcanic environments such as [[hot spring]]s are prized by industrial users for their ability to function at high temperatures, allowing enzyme-catalysed reactions to be operated at a very high rate.

Enzymes are usually much larger than their substrates. Sizes range from just 62 amino acid residues, for the [[monomer]] of [[4-Oxalocrotonate tautomerase|4-oxalocrotonate tautomerase]],<ref>{{cite journal | vauthors = Chen LH, Kenyon GL, Curtin F, Harayama S, Bembenek ME, Hajipour G, Whitman CP | title = 4-Oxalocrotonate tautomerase, an enzyme composed of 62 amino acid residues per monomer | journal = The Journal of Biological Chemistry | volume = 267 | issue = 25 | pages = 17716–17721 | date = September 1992 | pmid = 1339435 | doi = 10.1016/S0021-9258(19)37101-7 | doi-access = free }}</ref> to over 2,500 residues in the animal [[fatty acid synthase]].<ref>{{cite journal | vauthors = Smith S | title = The animal fatty acid synthase: one gene, one polypeptide, seven enzymes | journal = FASEB Journal | volume = 8 | issue = 15 | pages = 1248–1259 | date = December 1994 | pmid = 8001737 | doi = 10.1096/fasebj.8.15.8001737 | doi-access = free | s2cid = 22853095 }}</ref> Only a small portion of their structure (around 2–4 amino acids) is directly involved in catalysis: the catalytic site.<ref>{{cite web | url = http://www.ebi.ac.uk/thornton-srv/databases/CSA/ | title = The Catalytic Site Atlas | publisher = The European Bioinformatics Institute | access-date = 4 April 2007 | archive-date = 27 September 2018 | archive-url = https://web.archive.org/web/20180927214709/http://www.ebi.ac.uk/thornton-srv/databases/CSA/ | url-status = dead }}</ref> This catalytic site is located next to one or more [[binding site]]s where residues orient the substrates. The catalytic site and binding site together compose the enzyme's [[active site]]. The remaining majority of the enzyme structure serves to maintain the precise orientation and dynamics of the active site.<ref name = "Suzuki_2015_7">{{cite book | author = Suzuki H | title = How Enzymes Work: From Structure to Function | publisher = CRC Press | location = Boca Raton, FL | year = 2015 | isbn = 978-981-4463-92-8 | chapter = Chapter 7: Active Site Structure | pages = 117–140 }}</ref>

In some enzymes, no amino acids are directly involved in catalysis; instead, the enzyme contains sites to bind and orient catalytic [[cofactor (biochemistry)|cofactors]].<ref name="Suzuki_2015_7" /> Enzyme structures may also contain [[allosteric site]]s where the binding of a small molecule causes a [[conformational change]] that increases or decreases activity.<ref>{{cite book | author = Krauss G | title = Biochemistry of Signal Transduction and Regulation | date = 2003 | publisher = Wiley-VCH | location = Weinheim | isbn = 9783527605767 | edition = 3rd | pages = 89–114 | chapter = The Regulations of Enzyme Activity | chapter-url = https://books.google.com/books?id=iAvu2XRLnfYC&q=enzyme+metabolic+pathways+feedback+regulation&pg=PA91}}</ref>

A small number of [[Ribonucleic acid|RNA]]-based biological catalysts called [[ribozyme]]s exist, which again can act alone or in complex with proteins. The most common of these is the [[ribosome]] which is a complex of protein and catalytic RNA components.<ref name = "Stryer_2002"/>{{rp|2.2}}