Editing Enzyme (section)

===Functions of inhibitors===

In many organisms, inhibitors may act as part of a [[feedback]] mechanism. If an enzyme produces too much of one substance in the organism, that substance may act as an inhibitor for the enzyme at the beginning of the pathway that produces it, causing production of the substance to slow down or stop when there is sufficient amount. This is a form of [[negative feedback]]. Major metabolic pathways such as the [[citric acid cycle]] make use of this mechanism.<ref name = "Stryer_2002" />{{rp|17.2.2}}

Since inhibitors modulate the function of enzymes they are often used as drugs. Many such drugs are reversible competitive inhibitors that resemble the enzyme's native substrate, similar to [[methotrexate]] above; other well-known examples include [[statin]]s used to treat high [[cholesterol]],<ref name="Endo1992">{{cite journal | vauthors = Endo A | title = The discovery and development of HMG-CoA reductase inhibitors | journal = Journal of Lipid Research | volume = 33 | issue = 11 | pages = 1569–1582 | date = November 1992 | pmid = 1464741 | doi = 10.1016/S0022-2275(20)41379-3 | doi-access = free }}</ref> and [[protease inhibitors]] used to treat [[retroviral]] infections such as [[HIV]].<ref>{{cite journal | vauthors = Wlodawer A, Vondrasek J | title = Inhibitors of HIV-1 protease: a major success of structure-assisted drug design | journal = Annual Review of Biophysics and Biomolecular Structure | volume = 27 | pages = 249–284 | date = 1998 | pmid = 9646869 | doi = 10.1146/annurev.biophys.27.1.249 | s2cid = 10205781 }}</ref> A common example of an irreversible inhibitor that is used as a drug is [[aspirin]], which inhibits the [[Cyclooxygenase|COX-1]] and [[Cyclooxygenase|COX-2]] enzymes that produce the [[inflammation]] messenger [[prostaglandin]].<ref name="Johnson" /> Other enzyme inhibitors are poisons. For example, the poison [[cyanide]] is an irreversible enzyme inhibitor that combines with the copper and iron in the active site of the enzyme [[cytochrome c oxidase]] and blocks [[cellular respiration]].<ref>{{cite journal | vauthors = Yoshikawa S, Caughey WS | title = Infrared evidence of cyanide binding to iron and copper sites in bovine heart cytochrome c oxidase. Implications regarding oxygen reduction | journal = The Journal of Biological Chemistry | volume = 265 | issue = 14 | pages = 7945–7958 | date = May 1990 | pmid = 2159465 | doi = 10.1016/S0021-9258(19)39023-4 | doi-access = free }}</ref>