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== Cyclooxygenase 2 == | == Cyclooxygenase 2 == | ||
<Structure load='5kir' size='350' frame='true' align='right' caption='Human Cyclooxygenase 2 bound to Rofecoxib. PDB file 5KIR.' scene='' /> | <Structure load='5kir' size='350' frame='true' align='right' caption='Human Cyclooxygenase 2 bound to Rofecoxib. PDB file 5KIR.' scene='' /> | ||
A [[Cyclooxygenase]] is an enzyme that catalyzes the transformation of arachidonic acid into prostaglandins, prostacyclins, and thromboxanes.<ref name="Orlando">PMID:27710942</ref> Another name for cyclooxygenases is prostaglandin H2 synthase. There are two names because there are two catalytic activities: cyclooxygenase and peroxidase. The abbreviation for cyclooxygenase and prostaglandin H2 synthase is COX and PGHS respectively and can be used interchangeably. There are two types of cyclooxygenases: COX-1 and COX-2. COX-1 is responsible for platelet aggregation and gastric acidity.<ref name="Orlando" /> COX-2 is involved in pathways that lead to inflammation (swelling), pain, and fever.<ref name="Orlando" /> | A [[Cyclooxygenase]] is an enzyme that catalyzes the transformation of arachidonic acid into prostaglandins, prostacyclins, and thromboxanes.<ref name="Orlando">PMID:27710942</ref> Another name for cyclooxygenases is prostaglandin H2 synthase. There are two names because there are two catalytic activities: cyclooxygenase and peroxidase. The abbreviation for cyclooxygenase and prostaglandin H2 synthase is COX and PGHS respectively and can be used interchangeably. There are two types of cyclooxygenases: COX-1 and COX-2. COX-1 is responsible for platelet aggregation and gastric acidity.<ref name="Orlando" /> COX-2 is involved in pathways that lead to inflammation (swelling), pain, and fever.<ref name="Orlando" /> | ||
== Function == | == Function == | ||
===Reaction=== | |||
Cyclooxygenases catalyzes arachidonic acid or other fatty acids into prostaglandin H2 (PGH2) and other molecules that can be used for signal transduction. Of the two catalytic activities, the cyclooxygenase reaction happens before the peroxidase reaction. However, the peroxidase activity activates the cyclooxygenase activity.<ref name="Picot">PMID:8121489</ref> “Two-electron reduction of a peroxide substrate results in the oxidation of the ferric heme to an oxo-ferryl porphyrin radical cation.”<ref name="Rouzer">PMID:18952571</ref> The most important catalytic residue is Tyrosine 385. It transfers and electron to the heme to create the radical on the tyrosine <ref name="Rouzer" /> The tyrosine then takes the pro-S hydrogen from carbon 13 of arachidonic acid to produce a radical on the arachidonic intermediate. <ref name="Lehninger">"Chapter 21: Lipid Biosynthesis." ''Lehninger Principles of Biochemistry'', by David L. Nelson et al., Basingstoke, 2017, pp. 824-825.</ref> Two oxygen molecules are inserted to cyclize the intermediate.<ref name="Lehninger" /> Tyrosine 385 is reduced from the “peroxyl radical to the hyperoxide to form PGG2.”<ref name="Rouzer" /> PGG2 is then reduced by the peroxidase activity to form PGH2. (Lehninger). The Tyrosing 385 radical is regenerated, so the cyclooxygenase activity does not need to be activated for every reaction.<ref name="Rouzer" /> | Cyclooxygenases catalyzes arachidonic acid or other fatty acids into prostaglandin H2 (PGH2) and other molecules that can be used for signal transduction. Of the two catalytic activities, the cyclooxygenase reaction happens before the peroxidase reaction. However, the peroxidase activity activates the cyclooxygenase activity.<ref name="Picot">PMID:8121489</ref> “Two-electron reduction of a peroxide substrate results in the oxidation of the ferric heme to an oxo-ferryl porphyrin radical cation.”<ref name="Rouzer">PMID:18952571</ref> The most important catalytic residue is Tyrosine 385. It transfers and electron to the heme to create the radical on the tyrosine <ref name="Rouzer" /> The tyrosine then takes the pro-S hydrogen from carbon 13 of arachidonic acid to produce a radical on the arachidonic intermediate. <ref name="Lehninger">"Chapter 21: Lipid Biosynthesis." ''Lehninger Principles of Biochemistry'', by David L. Nelson et al., Basingstoke, 2017, pp. 824-825.</ref> Two oxygen molecules are inserted to cyclize the intermediate.<ref name="Lehninger" /> Tyrosine 385 is reduced from the “peroxyl radical to the hyperoxide to form PGG2.”<ref name="Rouzer" /> PGG2 is then reduced by the peroxidase activity to form PGH2. (Lehninger). The Tyrosing 385 radical is regenerated, so the cyclooxygenase activity does not need to be activated for every reaction.<ref name="Rouzer" /> | ||
