Editing Active site (section)

===Irreversible inhibitor: Diisopropyl fluorophosphate===

[[File:DIFP serine inactivation.svg|thumb|Irreversible inhibition of a serine protease by DIPF.|300px]]
[[Diisopropyl fluorophosphate]] (DIFP) is an irreversible inhibitor that blocks the action of [[serine protease]]. When it binds to the enzyme a [[nucleophilic substitution]] reaction occurs and releases one [[hydrogen fluoride]] molecule. The OH group in the active site acts as a nucleophile to attack the [[phosphorus]] in DIFP and form a tetrahedral intermediate and release a proton. Then the P-F bond is broken, one electron is transferred to the F atom and it leaves the intermediate as F<sup>−</sup> anion. It combines with a proton in solution to form one HF molecule. A covalent bond formed between the active site and DIFP, so the serine side chain is no longer available to the substrate.<ref name="JANSEN">{{cite journal|vauthors=Jansen EF, Nuttig F, Balls AK|date=1949|title=Mode of inhibition of chymotrypsin by diisopropyl fluorophosphate; introduction of phosphorus|journal=[[The Journal of Biological Chemistry]]|volume=179|issue=1|pages=201–204|doi=10.1016/S0021-9258(18)56828-9|pmid=18119235|doi-access=free}}</ref>