title: Inactivation of astrocytic glutamine synthetase by hydrogen peroxide requires iron.
abstract: The specific activity of brain glutamine synthetase (GS) is lowered in several neurodegenerative diseases that involve iron-mediated oxidative stress. The present study has investigated whether H₂O₂ directly inactivates GS or whether GS is primarily inactivated by hydroxyl radicals that are produced by the Fenton reaction when H₂O₂ reacts with ferrous iron. Exposure of purified sheep brain GS to supraphysiological concentrations of H₂O₂ (1 mM for 30 min) reduced its specific activity by only 41%, indicating that the enzyme is fairly resistant to oxidation by peroxide. However, the enzyme was completely inactivated when co-incubated with H₂O₂, iron and ascorbate, indicating a vulnerability to oxidation by conditions that favour the production of hydroxyl radicals. Similarly, specific GS activity in cultured mouse astrocytes was resistant to supraphysiological concentrations of H₂O₂, with approximately 37% of activity remaining 3h after incubation with 1mM H₂O₂. This inactivation was prevented by the iron chelators 2,2'-dipyridyl or 1,10-phenanthroline, but not by their non-chelating analogues. These data suggest that inactivation of astrocytic GS is caused by H₂O₂ indirectly via the Fenton reaction as it required the presence of chelatable intracellular iron.
authors.affiliation: Blood-Brain Interactions Group, School of Psychology and Psychiatry, Monash University, Victoria 3800, Australia.
authors.forename: S P
authors.initials: SP
authors.lastname: Fernandes
authors.forename: R
authors.initials: R
authors.lastname: Dringen
authors.forename: A
authors.initials: A
authors.lastname: Lawen
authors.forename: S R
authors.initials: SR
authors.lastname: Robinson
mesh_terms: D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D001921:Brain / Q000166:cytology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D016877:Oxidants / Q000494:pharmacology*; D010618:Phenanthrolines / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D016877:Oxidants; D010618:Phenanthrolines; D015082:2,2'-Dipyridyl; D006861:Hydrogen Peroxide; D007501:Iron; D007770:L-Lactate Dehydrogenase; D005974:Glutamate-Ammonia Ligase