Characterization of the lysyl adducts of prostaglandin H-synthases that are derived from oxygenation of arachidonic acid.

These investigations characterize the covalent binding of reactive products of prostaglandin H-synthases (PGHSs) to the enzyme and to other molecules. The intermediate product of oxygenation of arachidonic acid by the PGHSs, prostaglandin (PG) H2, undergoes rearrangement to the highly reactive gamma-keto aldehydes, levuglandin (LG) E2 and D2. We previously have demonstrated that LGE2 reacts with the epsilon-amine of lysine to form both the lysyl-levuglandin Shiff base and the pyrrole-derived lysyl-levuglandin lactam adducts. We now demonstrate that these lysyl-levuglandin adducts are formed on the PGHSs following the oxygenation of arachidonic acid; after reduction of the putative Schiff base, proteolytic digestion of the enzyme, and isolation of the adducted amino acid residues, these adducts were identified by liquid chromatography-tandem mass spectrometry. The reactivity of the LGs is reflected by the finding that virtually all of the LG predicted to be formed from PGH2 can be accounted for as adducts of the PGH-synthase and that oxygenation of arachidonic acid by PGH-synthases also leads to the formation of adducts of other proteins present in the reaction solution. The reactivity of the PGH-synthase adducts themselves is demonstrated by the formation of intermolecular cross-links.