title: The effects of nitric oxide on electron transport complexes.
abstract: The effect of nitric oxide on mitochondrial electron transfer complexes was studied by comparing the activities of nitric oxide-treated and untreated, deoxygenated samples of purified beef heart succinate-cytochrome c reductase, succinate-ubiquinone reductase, and ubiquinol-cytochrome c reductase. More than 90% of succinate-cytochrome c reductase activity is lost during nitric oxide treatment. The activity of the succinate-ubiquinone reductase component of succinate-cytochrome c reductase decreases 95%, while the ubiquinol-cytochrome c reductase component is unaffected by nitric oxide. This inactivation is due primarily to the destruction of iron-sulfur clusters from succinate-ubiquinone reductase. When purified beef heart succinate-ubiquinone reductase was treated with nitric oxide, virtually all activity was irreversibly lost. The electron paramagnetic resonance (EPR) spectra of the treated complex showed typical iron-nitric oxide complex signals, confirming that inactivation is due to destruction of the iron-sulfur clusters. Similar results were obtained with purified Escherichia coli succinate-ubiquinone reductase. Pure beef heart ubiquinol-cytochrome c reductase treated with nitric oxide loses 40% of its initial activity, but regains most of it (90-100 % after 24 h of incubation at 0 degrees C in the absence of nitric oxide. This suggests that ubiquinol-cytochrome c reductase is protected from nitric oxide when complexed with succinate-ubiquinone reductase or that when split from succinate-ubiquinone reductase, ubiquinol-cytochrome c reductase undergoes a conformational change which allows access of nitric oxide to the Rieske iron-sulfur center. Such access is not possible when ubiquinol-cytochrome c reductase is complexed with succinate-ubiquinone reductase. The loss of ubiquinol-cytochrome c reductase activity correlates with a decrease in the Rieske protein EPR signal intensity without formation of any new EPR signal. The Rieske iron-sulfur cluster signal is recovered after 24 h incubation in the absence of nitric oxide.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater 74078, USA.
authors.forename: R
authors.initials: R
authors.lastname: Welter
authors.forename: L
authors.initials: L
authors.lastname: Yu
authors.forename: C A
authors.initials: CA
authors.lastname: Yu
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport / Q000187:drug effects*; D042963:Electron Transport Complex II; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology; D009569:Nitric Oxide / Q000494:pharmacology*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D013384:Succinate Cytochrome c Oxidoreductase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D007506:Iron-Sulfur Proteins; D009097:Multienzyme Complexes; D009569:Nitric Oxide; D010088:Oxidoreductases; D013384:Succinate Cytochrome c Oxidoreductase; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; D014450:Electron Transport Complex III