| 20006572 |
Unitt DC, Hollis VS, Palacios-Callender M, Frakich N, Moncada S: Inactivation of nitric oxide by cytochrome c oxidase under steady-state oxygen conditions. Biochim Biophys Acta. 2010 Mar;1797(3):371-7. Epub 2009 Dec 16.
We have developed a respiration chamber that allows intact cells to be studied under controlled oxygen (O (2)) conditions. The system measures the concentrations of O (2) and nitric oxide (NO) in the cell suspension, while the redox state of cytochrome c oxidase is continuously monitored optically. Using human embryonic kidney cells transfected with a tetracycline-inducible NO synthase we show that the inactivation of NO by cytochrome c oxidase is dependent on both O (2) concentration and electron turnover of the enzyme. At a high O (2) concentration (70 microM), and while the enzyme is in turnover, NO generated by the NO synthase upon addition of a given concentration of l-arginine is partially inactivated by cytochrome c oxidase and does not affect the redox state of the enzyme or consumption of O (2). At low O (2) (15 microM), when the cytochrome c oxidase is more reduced, inactivation of NO is decreased. In addition, the NO that is not inactivated inhibits the cytochrome c oxidase, further reducing the enzyme and lowering O (2) consumption. At both high and low O (2) concentrations the inactivation of NO is decreased when sodium azide is used to inhibit cytochrome c oxidase and decrease electron turnover. |
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