Prostanoid

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Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins (active in the resolution phase of inflammation.)

Biosynthesis[edit]

Cyclooxygenase (COX) catalyzes the conversion of the free essential fatty acids to prostanoids by a two-step process. In the first step, two molecules of O2 are added as two peroxide linkages and a 5-member carbon ring is forged near the middle of the fatty acid chain. This forms the short-lived, unstable intermediate Prostaglandin G (PGG). One of the peroxide linkages sheds a single oxygen, forming PGH. (See diagrams and more detail at Cyclooxygenase). All other prostanoids originate from PGH (as PGH1, PGH2, or PGH3).

Figure 1 shows how PGH2 (derived from Arachidonic acid) is converted:

The three classes of prostanoids have distinctive rings in the center of the molecule. They differ in their structures. The PGH compounds (parents to all the rest) have a 5-carbon ring, bridged by two oxygens (a peroxide.) The derived prostaglandins contain a single, unsaturated 5-carbon ring. In prostacyclins, this ring is conjoined to another oxygen-containing ring. In thromboxanes the ring becomes a 6-member ring with one oxygen.

Production of PGE2 in bacterial and viral infections appear to be stimulated by certain cytokines, e.g., interleukin-1.[1]

See also[edit]

References[edit]

  1. ^ University of Kansas Medical Center (2004). "Eicosanoids and Inflammation" (PDF). Retrieved 2007-01-05. [dead link]