Prostaglandin H synthase-2-catalyzed oxygenation of 2-arachidonoylglycerol is more sensitive to peroxide tone than oxygenation of arachidonic acid.

Musee J, Marnett LJ
J Biol Chem. 2012 287 (44): 37383-94

PMID: 22942274 · PMCID: PMC3481335 · DOI:10.1074/jbc.M112.381202

The endocannabinoid, 2-arachidonoylglycerol (2-AG), is a selective substrate for the inducible isoform of prostaglandin H synthase (PGHS), PGHS-2. Its turnover leads to the formation of glyceryl esters of prostaglandins (PG-Gs), a subset of which elicits agonism at unique, as yet unidentified, receptors. The k(cat)/K(m) values for oxygenation of arachidonic acid (AA) and 2-AG by PGHS-2 are very similar, but the sensitivities of the two substrates to peroxide-dependent activation have not been compared. 15-Hydroperoxy derivatives of AA and 2-AG were found to be comparable in their ability to serve as substrates for the peroxidase activities of PGHS-2, PGHS-1, and glutathione peroxidase (GPx). They also were comparable in the activation of AA oxygenation by cyanide-inhibited PGHS-2. However, oxygenation of 2-AG was significantly suppressed relative to AA by the presence of GPx and GSH. Furthermore, 2-AG oxygenation by peroxidase-deficient H388YmPGHS-2 was much less efficient than AA oxygenation. Wild-type rates of 2-AG oxygenation were restored by treatment of H388YmPGHS-2 with hydroperoxide derivatives of AA or 2-AG. RNAi silencing of phospholipid hydroperoxide-specific GPx (GPx4) in NIH/3T3 cells led to increases in cellular peroxidation and in the levels of the isoprostane product, 8-epi-PGF(2α). GPx4 silencing led to 2-4-fold increases in PG-G formation but no change in PG formation. Thus, cellular peroxide tone may be an important determinant of the extent of endocannabinoid oxygenation by PGHS-2.

MeSH Terms (25)

Amino Acid Substitution Animals Arachidonic Acid Arachidonic Acids Benzothiazoles Biocatalysis Cattle Chromogenic Compounds Cyclooxygenase 1 Cyclooxygenase 2 Endocannabinoids Enzyme Activation Gene Knockdown Techniques Glutathione Peroxidase Glycerides Humans Kinetics Mice NIH 3T3 Cells Oxidation-Reduction Oxidative Stress Peroxides Prostaglandins RNA Interference Sulfonic Acids

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