Biomaterial Database

Mechanism for irreversible self-deactivation of prostaglandin synthetase. 1976

R W Egan, and J Paxton, and F A Kuehl

It has been shown that prostaglandin (PG) cyclooxygenase is irreversibly self-deactivated during the oxygenation of arachidonic acid (Smith, W. L., and Lands, W.E.M. (1972) Biochemistry II, 3273-3285). Using several experimental approaches and an enzyme preparation which was highly active without artificial stimulation, we have extensively investigated the mechanism of this deactivation process. During the generation of PGH2 from arachidonic acid, oxidizing equivalents were released and the reductive breakdown of PGG2 was found to deactivate the cyclooxygenase. The cyclooxygenase-catalyzed metabolism of both arachidonic acid and PGG2 generated radicals which were scavenged by phenol. Both phenol and methional (scavengers of oxygen-centered radicals) promoted the formation of PGH2 at the expense of PGG2 and increased the initial rate and the extent of reaction prior to deactivation of the cyclooxygenase. Hence, it appears that the cyclooxygenase was irreversibly self-deactivated during the formation of PGH2 from arachidonic acid, due to its oxidation by oxygen-centered radicals formed as a result of the reductive breakdown of the hydroperoxide on PGG2. Some experiments with dithiothereitol and N-ethylmaleimide suggested that the enzyme may contain a disulfide at the active site. A mechanism has been devised which accounts for the self-deactivation phenomenon, the effect of phenol and methional, the disulfide at the active site, and the pathway of substrate oxygenation.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008297	Male		Males
D008861	Microsomes	Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)	Microsome
D010636	Phenols	Benzene derivatives that include one or more hydroxyl groups attached to the ring structure.
D011451	Prostaglandin-Endoperoxide Synthases	Enzyme complexes that catalyze the formation of PROSTAGLANDINS from the appropriate unsaturated FATTY ACIDS, molecular OXYGEN, and a reduced acceptor.	Fatty Acid Cyclo-Oxygenase,PGH Synthase,Prostaglandin H Synthase,Prostaglandin Synthase,Prostaglandin-Endoperoxide Synthase,Arachidonic Acid Cyclooxygenase,Cyclo-Oxygenase,Cyclooxygenase,Cyclooxygenases,Hydroperoxide Cyclase,PGH2 Synthetase,Prostaglandin Cyclo-Oxygenase,Prostaglandin Cyclooxygenase,Prostaglandin Endoperoxide Synthetase,Prostaglandin G-H Synthase,Prostaglandin H2 Synthetase,Prostaglandin Synthetase,Cyclase, Hydroperoxide,Cyclo Oxygenase,Cyclo-Oxygenase, Fatty Acid,Cyclo-Oxygenase, Prostaglandin,Cyclooxygenase, Arachidonic Acid,Cyclooxygenase, Prostaglandin,Endoperoxide Synthetase, Prostaglandin,Fatty Acid Cyclo Oxygenase,G-H Synthase, Prostaglandin,Prostaglandin Cyclo Oxygenase,Prostaglandin Endoperoxide Synthases,Prostaglandin G H Synthase,Synthase, PGH,Synthase, Prostaglandin,Synthase, Prostaglandin G-H,Synthase, Prostaglandin H,Synthase, Prostaglandin-Endoperoxide,Synthases, Prostaglandin-Endoperoxide,Synthetase, PGH2,Synthetase, Prostaglandin,Synthetase, Prostaglandin Endoperoxide,Synthetase, Prostaglandin H2
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D004229	Dithiothreitol	A reagent commonly used in biochemical studies as a protective agent to prevent the oxidation of SH (thiol) groups and for reducing disulphides to dithiols.	Cleland Reagent,Cleland's Reagent,Sputolysin,Clelands Reagent,Reagent, Cleland,Reagent, Cleland's
D005033	Ethylmaleimide	A sulfhydryl reagent that is widely used in experimental biochemical studies.	N-Ethylmaleimide,N Ethylmaleimide
D006899	Mixed Function Oxygenases	Widely distributed enzymes that carry out oxidation-reduction reactions in which one atom of the oxygen molecule is incorporated into the organic substrate; the other oxygen atom is reduced and combined with hydrogen ions to form water. They are also known as monooxygenases or hydroxylases. These reactions require two substrates as reductants for each of the two oxygen atoms. There are different classes of monooxygenases depending on the type of hydrogen-providing cosubstrate (COENZYMES) required in the mixed-function oxidation.	Hydroxylase,Hydroxylases,Mixed Function Oxidase,Mixed Function Oxygenase,Monooxygenase,Monooxygenases,Mixed Function Oxidases,Function Oxidase, Mixed,Function Oxygenase, Mixed,Oxidase, Mixed Function,Oxidases, Mixed Function,Oxygenase, Mixed Function,Oxygenases, Mixed Function
D000332	Aerobiosis	Life or metabolic reactions occurring in an environment containing oxygen.	Aerobioses