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Mitochondrial nitric oxide synthase is constitutively active and is functionally upregulated in hypoxia
Z Lacza1, M Puskar, J P Figueroa
1Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. zlacza@wfubmc.edu
Free Radical Biology & Medicine
|December 18, 2001
Summary
Mitochondrial nitric oxide synthase (mtNOS) exists in mouse tissues and is activated by hypoxia. This enzyme, similar to endothelial nitric oxide synthase (eNOS), plays a role in mitochondrial regulation during low oxygen conditions.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Nitric oxide (NO) influences mitochondrial functions like respiration and ATP synthesis.
- The existence and physiological role of mitochondrial nitric oxide synthase (mtNOS) remain debated.
- mtNOS may be a novel enzyme isoform involved in cellular signaling.
Purpose of the Study:
- To confirm the presence and distribution of mtNOS in mouse tissues.
- To characterize mtNOS by examining its cross-reactivity with NOS antibodies.
- To investigate the impact of hypoxia on mtNOS activity.
Main Methods:
- Utilized three independent methods to detect mtNOS.
- Measured NOS activity via arginine to citrulline conversion in isolated mitochondria.
- Employed immunoblotting and immunogold labeling with electron microscopy.
Main Results:
- Significant mtNOS activity was found in brain mitochondria, higher than in liver mitochondria.
- mtNOS activity was inhibited by calmidazolium, a calmodulin inhibitor.
- Hypoxia significantly increased mtNOS activity compared to normoxic conditions.
- Antibodies against endothelial NOS (eNOS) recognized mtNOS, confirmed by electron microscopy localization.
Conclusions:
- mtNOS is a constitutively active, eNOS-like isoform present in mouse mitochondria.
- mtNOS activity is modulated by cellular conditions, notably hypoxia.
- This isoform likely contributes to mitochondrial regulation under hypoxic stress.