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Oxygen-dependent reversible inhibition of mitochondrial respiration by nitric oxide
Y Takehara1, H Nakahara, Y Inai
1Institute of Medical Science, Center for Adult Diseases, Kurashiki, Japan.
Abstract:
Effects of nitric oxide (NO) and NO generating agents, on the electron transport system of mitochondria were examined in a study of the mechanism and physiological importance of NO in energy metabolism. In the presence of various substrates, uncoupled respiration was inhibited by NO in manner which was both dose- and oxygen tension-dependent. Simultaneously measuring changes in cytochrome absorption spectra and respiration showed that the site of action of NO is cytochrome oxidase. Similar inhibition was also brought about by 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18), an NO donor. Electron paramagnetic resonance (EPR) analysis revealed that inhibition of uncoupled respiration occurred only during the presence of NO in the reaction mixture. The inhibitory effect of NO was increased significantly by lowering the concentration of mitochondrial protein. No appreciable inhibition of respiration was observed in the presence of 3-morpholinosydnonimine (SIN-1), a peroxynitrite anion (ONOO-) generating reagent, but inhibition did occur in the presence of superoxide dismutase (SOD). These results indicate that NO reversibly interacts with mitochondria at complex IV thereby inhibiting respiration particularly under physiologically low oxygen tension and that de novo generated ONOO may have no significant effect under the present experimental conditions.
Insights
Nitric oxide (NO) reversibly inhibits mitochondrial respiration at complex IV, particularly under low oxygen conditions. This NO effect on the electron transport system is dose- and oxygen-dependent.
Area of Science:
- Biochemistry
- Cellular Respiration
- Mitochondrial Function
Background:
- Nitric oxide (NO) plays a crucial role in cellular energy metabolism.
- Understanding the precise mechanisms of NO's interaction with mitochondria is vital for physiological insights.
Purpose of the Study:
- To investigate the effects of nitric oxide (NO) and NO-generating agents on mitochondrial electron transport.
- To elucidate the mechanism and physiological significance of NO in energy metabolism.
Main Methods:
- Mitochondrial respiration assays with various substrates.
- Spectrophotometric analysis of cytochrome absorption.
- Electron paramagnetic resonance (EPR) spectroscopy.
- Use of NO donors (NOC 18) and peroxynitrite generators (SIN-1).
Main Results:
- NO inhibited uncoupled mitochondrial respiration in a dose- and oxygen tension-dependent manner.
- NO was found to act specifically at cytochrome oxidase (Complex IV).
- Inhibition was potentiated at lower mitochondrial protein concentrations and was reversible.
Conclusions:
- Nitric oxide (NO) reversibly interacts with mitochondria at Complex IV, inhibiting respiration.
- This inhibition is most pronounced under physiologically low oxygen tensions.
- Peroxynitrite anion (ONOO-) generation did not significantly inhibit respiration under these experimental conditions.