Prostaglandin H₂ is a type of

prostaglandin The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derive ...

and a precursor for many other biologically significant molecules. It is synthesized from arachidonic acid in a reaction catalyzed by a

cyclooxygenase Cyclooxygenase (COX), officially known as prostaglandin-endoperoxide synthase (PTGS), is an enzyme (specifically, a family of isozymes, ) that is responsible for formation of prostanoids, including thromboxane and prostaglandins such as pr ...

enzyme. The conversion from Arachidonic acid to Prostaglandin H2 is a two step process. First,

COX-1 Cyclooxygenase 1 (COX-1), also known as prostaglandin G/H synthase 1, prostaglandin-endoperoxide synthase 1 or prostaglandin H2 synthase 1, is an enzyme that in humans is encoded by the ''PTGS1'' gene. In humans it is one of two cyclooxygenases. ...

catalyzes the addition of two free oxygens to form the 1,2-Dioxane bridge and a peroxide functional group to form

Prostaglandin G2 Prostaglandin G2 is an organic peroxide belonging to the family of prostaglandins. The compound has been isolated as a solid, although it is usually used in vivo. It quickly converts into prostaglandin H2, a process catalyzed by the enzyme COX. ...

. Second,

COX-2 Prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase) (The HUGO official symbol is PTGS2; HGNC ID, HGNC:9605), also known as cyclooxygenase-2 or COX-2, is an enzyme that in humans is encoded by the ''PTGS2'' gene ...

reduces the peroxide functional group to a

Secondary alcohol In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...

, forming Prostaglandin H2. Other peroxidases like

Hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para'' ...

have been observed to reduce PGG2 to PGH2. PGH2 is unstable at room temperature, with a half life of 90-100 seconds, so it is often converted into a different prostaglandin. It is acted upon by: *

Prostacyclin synthase Prostaglandin-I synthase () also known as prostaglandin I2 (prostacyclin) synthase (PTGIS) or CYP8A1 is an enzyme involved in prostanoid biosynthesis that in humans is encoded by the ''PTGIS'' gene. This enzyme belongs to the family of cytochrome ...

to create

prostacyclin Prostacyclin (also called prostaglandin I2 or PGI2) is a prostaglandin member of the eicosanoid family of lipid molecules. It inhibits platelet activation and is also an effective vasodilator. When used as a drug, it is also known as epoprosteno ...

Thromboxane-A synthase Thromboxane A synthase 1 (, platelet, cytochrome P450, family 5, subfamily A), also known as TBXAS1, is a cytochrome P450 enzyme that, in humans, is encoded by the ''TBXAS1'' gene. Function This gene encodes a member of the cytochrome P450 supe ...

to create

thromboxane A2 Thromboxane A2 (TXA2) is a type of thromboxane that is produced by activated platelets during hemostasis and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation. This is achieved by act ...

and 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (HHT) (see 12-Hydroxyheptadecatrienoic acid) *

Prostaglandin D2 synthase Prostaglandin-H2 D-isomerase (PTGDS) is an enzyme that in humans is encoded by the ''PTGDS'' gene. Function The protein encoded by this gene is a glutathione-independent prostaglandin D synthase that catalyzes the conversion of prostaglandin ...

to create prostaglandin D2 *

Prostaglandin E synthase Prostaglandin E synthase (, or PGE synthase) is an enzyme involved in eicosanoid and glutathione metabolism, a member of MAPEG family. It generates prostaglandin E (PGE) from prostaglandin H2. The synthase generating PGE2 is a membrane-associat ...

to create prostaglandin E2 It rearranges non-enzymatically to: * A mixture of 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (HHT) and 12-(S)-hydroxy-5Z,8Z,10E-heptadecatrienoic acid (see 12-Hydroxyheptadecatrienoic acid) Use of prostaglandin H₂: * regulating the constriction and dilation of blood vessels * stimulating platelet aggregation **binds to

Thromboxane receptor The thromboxane receptor (TP) also known as the prostanoid TP receptor is a protein that in humans is encoded by the ''TBXA2R'' gene, The thromboxane receptor is one among the five classes of prostanoid receptors and was the first eicosanoid rec ...

on platelets' cell membranes to trigger platelet migration and adhesion to other platelets. Effects of Aspirin on prostaglandin H₂: * Aspirin has been hypothesized to block the conversion of arachidonic acid to prostaglandin

References

Organic peroxides Prostaglandins {{biochemistry-stub