Prostaglandin endoperoxide synthase, reaction catalyzed

Studies of the biosynthesis of PGE2 from arachidonic acid have shown that all three oxygens come from O2. The enzyme involved, prostaglandin endoperoxide synthase, has cyclooxygenase (COX) activity and catalyzes the reaction of arachidonic acids with O2 to give an endoperoxide (PGG2). 

Reaction catalyzed by prostaglandin endoperoxide synthase. This enzyme has two catalytic activities, as indicated next to the reaction arrows. 

Prostaglandin endoperoxide H2 synthase (PGHS) [EC 1.14.99.1] isoenzymes 1 and 2 catalyze the committed step in prostanoid synthesis via two sequential enzymatic reactions... 

D. The first step in the synthesis of prostaglandins and thromboxanes is the reaction catalyzed by the cyclooxygenase activity of PGH synthase. This reaction canses the cyclization of the fatty acid while at the same time introdncing an nnstable endoperoxide between carbons 9 and 10 and a hydroperoxide at carbon 15 to prodnce PGG2, which is rapidly rednced to PGH by the peroxidase activity of PGH synthase. 

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