Prostaglandin H Synthase: Perturbation of the Tyrosyl Radical as a Probe of Anti-Cyclooxygenase Agents
Prostaglandin H synthase exhibits two distinct catalytic activities. A cyclooxygenase activity that incorporates two molecules of molecular oxygen into arachidonic acid to form prostaglandin (PG) G2, and a rather nonspecific heme-dependent peroxidase that reduces hydoperoxides (e.g. PGG2) to the corresponding alcohols (e.g. PGH2) at the expense of an electron donor. The conversion of arachidonate to PGG2 in the cyclooxygenase reaction is believed to proceed via a free radical reaction mechanism that is initiated by the abstraction of a hydrogen atom from C13 of the fatty acid to form a fatty acyl free radical (Hamberg and Samuelsson, 1967). Rearrangement of the fatty acyl backbone and attack on molecular oxygen follow in a concerted fashion to give PGG2. The role of the synthase in this conversion is presumably to furnish the oxidant necessary for abstraction of the C13 hydrogen atom, and to bind the fatty acid in an arrangement that determines the stereochemical outcome. The identity of the enzyme oxidant responsible is a key question in the study of the cyclooxygenase catalytic mechanism.
KeywordsCyclooxygenase Activity Prostaglandin Endoperoxide Tyrosyl Radical Tyrosyl Residue Tyrosine Radical
Unable to display preview. Download preview PDF.
- DeWitt, D.L., and Smith, W.L., 1988, Primary structure of prostaglandin G/H synthase from sheep vesicular gland determined from the complementary DNA sequence, prof. Natl. Acad. Sci. USA 85: 1412–1416.Google Scholar
- Hemler, M.E., Crawford, C.G., and Lands, W.E.M., 1978, Lipoxygenation activity of purified prostaglandin forming cyclooxygenase, Biochemistry 17: 1772–1779.Google Scholar
- Karthein, R., Dietz, R., Nastainczyk, W., and Ruf, H.H., 1988, Higher oxidation states of prostaglandin H synthase, Eur. J. Biochem. 171: 313–320.Google Scholar
- Kulmacz, R.J., 1986, Prostaglandin H synthase and hydroperoxides: peroxidase reaction and inactivation kinetics, Arch. Biochem. Biophys. 249: 273–285.Google Scholar
- Kulmacz, R.J., and Lands, W.E.M., 1985, Stoichiometry and kinetics of the interaction of prostaglandin H synthase with anti-inflammatory agents, J. Biol. Chem. 260: 12572–12578.Google Scholar
- Kulmacz, R.J., Ren, Y., Tsai, A.-L., and Palmer, G., 1990a, Prostaglandin H synthase: spectroscopic studies of the interaction with hydroperoxides and with indomethacin, Biochemistry 29: 8760–8771.Google Scholar
- Kulmacz,R.J., Ren, Y., Tsai, A.-L., and Palmer, G., 1990b, PGH synthase: interactions with hydroperoxides and indomethacin, Adv. Prost. Thromb. Leuk. Res. 21: 137–140.Google Scholar
- Kulmacz, R.J., Tsai, A.-L., and Palmer, G., 1987, Heme spin states and peroxide-induced radical species in prostaglandin H synthase, J. Biol. Chem . 262: 10524–10531.Google Scholar
- Miles, E.W., 1977, Modification of histidyl residues in proteins by diethylpyrocarbonate, Methods Enzymo1.47: 431–442.Google Scholar
- Shimokawa, T., Kulmacz, R.J., DeWitt, D.L., and Smith, W.L., 1990, Tyrosine 385 of prostaglandin endoperoxide synthase is required for cyclooxygenase catalysis, J.Biol. Chem. 265: 20073–20076.Google Scholar
- Smith,W.L., DeWitt, D.L., Kraemer, S.A., Andrews, M.J., Hla, T., Maciag, T., and Shimokawa, T., 1990, Structure-functionGoogle Scholar
- relationships in sheep, mouse, and human prostaglandin endoperoxide G/H synthases, Adv. Prost Thromb. Leuk. Res. 20: 14–21.Google Scholar