Spectroscopic Evidence for Reaction of Prostaglandin H Synthase-1 Tyrosyl Radical with Arachidonic Acid
作者： Ah-lim Tsai , Richard J. Kulmacz , Graham Palmer
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摘要: The coupling between the peroxidase and cyclooxygenase activities of prostaglandin H synthase (PGHS) has been proposed to be mediated by a critical tyrosyl radical through branched chain mechanism (Dietz, R., Nastainczyk, W., Ruf, H. (1988) Eur. J. Biochem. 171, 321-328). In this study, we have examined ability PGHS isoform-1 (PGHS-1) radicals react with arachidonate. Anaerobic addition arachidonate following formation peroxide-induced wide doublet or singlet led disappearance emergence new EPR signal, which is distinct from known PGHS-1 radicals. was clearly derived because its line shape changed when 5,6,8,9,11,12,14,15-octadeuterated used. Subsequent oxygen samples containing fatty acyl resulted in regeneration EPR. contrast, peroxide-generated indomethacin-treated (a narrow singlet) failed arachidonate, consistent inhibition indomethacin. These results indicate that serve as immediate oxidants bound at active site form carbon-centered radical, reacts hydroperoxide. observations represent first direct evidence chemical reaction oxygenation support role for catalysis.
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