title: Higher oxidation states of prostaglandin H synthase. Rapid electronic spectroscopy detected two spectral intermediates during the peroxidase reaction with prostaglandin G2.
abstract: The reaction of prostaglandin H synthase with prostaglandin G2, the physiological substrate for the peroxidase reaction, was examined by rapid reaction techniques at 1 degree C. Two spectral intermediates were observed and assigned to higher oxidation states of the enzymes. Intermediate I was formed within 20 ms in a bimolecular reaction between the enzyme and prostaglandin G2 with k1 = 1.4 x 10(7) M-1 s-1. From the resemblance to compound I of horseradish peroxidase, the structure of intermediate I was assigned to [(protoporphyrin IX)+.FeIVO]. Between 10 ms and 170 ms intermediate II was formed from intermediate I in a monomolecular reaction with k2 = 65 s-1. Intermediate II, spectrally very similar to compound II of horseradish peroxidase or complex ES of cytochrome-c peroxidase, was assigned to a two-electron oxidized state [(protoporphyrin IX)FeIVO] Tyr+. which was formed by an intramolecular electron transfer from tyrosine to the porphyrin-pi-cation radical of intermediate I. A reaction scheme for prostaglandin H synthase is proposed where the tyrosyl radical of intermediate II activates the cyclooxygenase reaction.
mesh_terms: D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism; D011449:Prostaglandin Endoperoxides / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011462:Prostaglandins G / Q000378:metabolism*; D012756:Sheep; D013057:Spectrum Analysis; D014443:Tyrosine
chemical_list: D001095:Arachidonic Acids; D011449:Prostaglandin Endoperoxides; D011462:Prostaglandins G; D016718:Arachidonic Acid; D014443:Tyrosine; C038291:prostaglandin G2; D006861:Hydrogen Peroxide; D010544:Peroxidases; D011451:Prostaglandin-Endoperoxide Synthases