Related Experiment Videos
Functional implications of nitric oxide produced by mitochondria in mitochondrial metabolism
1Department of Molecular Pharmacology and Toxicology, University of Southern California, 1985 Zonal Ave., Los Angeles, CA 90033, USA. cgiulivi@hsc.edu
Abstract:
The effects of endogenous production of NO., catalysed by the mitochondrial nitric oxide synthase (NOS), on mitochondrial metabolism were studied. The respiratory rates of intact mitochondria in State 4 were decreased by 40% and 28% with succinate and malate-glutamate, respectively, in the presence of L-arginine (L-Arg); conversely, the O2 uptake with NG-methyl-L-arginine (NMMA), a competitive inhibitor of NOS, was increased. The production of NO. and the inhibition of the respiratory rates were dependent on the metabolic state in which mitochondria were maintained: NO. production was probably supported by mitochondrial NADPH, the latter maintained by the energy-dependent transhydrogenase. In addition to the decline in the respiratory rate, an inhibition of ATP synthesis was also observed (40-50%) following supplementation with L-Arg. The dependence of the respiratory rates of mitochondria in State 3 and cytochrome oxidase activities on O2 concentrations with either L-Arg or NMMA indicated that both processes were competitively inhibited by NO. at the cytochrome oxidase level. This inhibition can be explained by the interaction of NO. with cytochrome oxidase at the binuclear centre. The role of NO. as a physiological modulator of cytochrome oxidase is discussed in terms of cellular metabolism.
Insights
Endogenous nitric oxide (NO.) production, catalyzed by mitochondrial nitric oxide synthase (NOS), inhibits mitochondrial respiration and ATP synthesis by interacting with cytochrome oxidase. This highlights NO.
Area of Science:
- Mitochondrial Physiology
- Biochemistry
- Cellular Metabolism
Background:
- Mitochondrial nitric oxide synthase (NOS) produces nitric oxide (NO.).
- The role of endogenously produced NO. in regulating mitochondrial function is not fully understood.
Purpose of the Study:
- To investigate the effects of endogenous NO. production on mitochondrial metabolism.
- To elucidate the mechanism by which NO. influences mitochondrial respiration and ATP synthesis.
Main Methods:
- Measurement of mitochondrial respiratory rates (State 4 and State 3) in the presence of L-arginine (L-Arg) and NG-methyl-L-arginine (NMMA).
- Assessment of ATP synthesis inhibition.
- Analysis of cytochrome oxidase activity under varying oxygen concentrations.
- Investigation of NO. production dependence on mitochondrial metabolic state and NADPH.
Main Results:
- L-Arg supplementation decreased State 4 respiratory rates by 40% (succinate) and 28% (malate-glutamate), while NMMA increased O2 uptake.
- NO. production and respiratory inhibition were dependent on the mitochondrial metabolic state, likely supported by NADPH via transhydrogenase.
- ATP synthesis was inhibited by 40-50% with L-Arg.
- NO. competitively inhibited State 3 respiration and cytochrome oxidase activity at the cytochrome oxidase level, suggesting interaction at the binuclear center.
Conclusions:
- Endogenous NO. production significantly inhibits mitochondrial respiration and ATP synthesis.
- NO. acts as a physiological modulator of cytochrome oxidase, impacting cellular energy metabolism.
- The findings provide insight into the regulatory role of NO. in mitochondrial function.