GO:0008941 nitric oxide dioxygenase [NAD(P)H] activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008941 describes the molecular function that catalyzes 2 NO + 2 O2 + NAD(P)H + H+ = 2 nitrate + NAD(P)+, converting toxic nitric oxide into nitrate.
• Flavohemoglobins are the best-characterized enzymes with this activity, using a heme-bound dioxygen intermediate to oxidize NO.
• The B10 tyrosine hydroxyl and distal heme pocket residues are essential for dioxygen binding and catalytic turnover.
• Nitric oxide dioxygenase activity protects aerobic cells from NO toxicity and is sensitive to inhibition by NO, CO, and imidazole antibiotics.
• Mycobacterium tuberculosis HbN and Synechococcus hemoglobin are alternative heme proteins that exhibit NO dioxygenase chemistry.
• CRISPR knockout, point-mutation, knock-in, and overexpression models enable causal testing of NOD-encoding genes in NO resistance and host-pathogen interactions.
Description
Nitric oxide (NO) is a reactive free radical that serves as a signaling molecule but becomes cytotoxic at high concentrations. The enzyme activity defined by GO:0008941, nitric oxide dioxygenase [NAD(P)H] activity, catalyzes the oxidation of NO to nitrate using molecular oxygen and NAD(P)H as electron donor. This activity is widely distributed in bacteria, fungi, and higher organisms, where it provides a primary defense against nitrosative stress. The reaction consumes two molecules of NO, two molecules of O2, one NAD(P)H, and one proton to produce two nitrate ions and NAD(P)+. Because NO is central to host immunity, neurotransmission, and vascular tone, understanding how cells detoxify it is of broad biomedical importance. Researchers study this activity to dissect microbial pathogenesis, NO signaling, and the evolution of heme-based sensors and detoxifiers.
nitric oxide dioxygenase [NAD(P)H] activity At A Glance
| GO ID | GO:0008941 |
|---|---|
| GO term | nitric oxide dioxygenase [NAD(P)H] activity |
| Ontology | molecular_function |
| Synonym | nitric oxide dioxygenase activity; NOD activity |
| Definition | Catalysis of the reaction: 2 NO + 2 O2 + NAD(P)H + H+ = 2 nitrate + NAD(P)+. |
| Major function | Detoxification of nitric oxide by oxidation to nitrate, protecting cells from nitrosative stress. |
| Representative enzymes | Flavohemoglobins (e.g., Hmp in E. coli), HbN in M. tuberculosis, and related heme proteins. |
| Cofactors | Heme (iron protoporphyrin IX) and FAD/FMN in flavohemoglobins; NAD(P)H as electron donor. |
| Subcellular context | Cytosolic in bacteria; in eukaryotes often associated with cytosolic or mitochondrial compartments depending on the organism. |
What Is GO:0008941?
GO:0008941 is a molecular function term describing the catalysis of the reaction: 2 NO + 2 O2 + NAD(P)H + H+ = 2 nitrate + NAD(P)+. In other words, it is the NAD(P)H-dependent oxidation of nitric oxide to nitrate, typically carried out by heme-containing flavohemoglobins or related hemoglobins that bind oxygen and NO in a coordinated catalytic cycle.
Why Is nitric oxide dioxygenase [NAD(P)H] activity Important in Cell Biology?
Nitric oxide dioxygenase activity is a central mechanism for NO detoxification and is critical for microbial survival inside host phagocytes, where NO is a key antimicrobial effector. In higher organisms, related globins may modulate NO signaling and protect tissues from nitrosative damage. The activity also serves as a paradigm for heme-based catalysis and for understanding how pathogens resist host immunity.
• Protects aerobic cells from NO-mediated inhibition of respiration and DNA damage.
• Enables pathogens such as Mycobacterium tuberculosis to survive host-derived NO.
• Provides a model for heme protein catalysis and oxygen activation.
• Is inhibited by CO and imidazole antibiotics, linking it to antimicrobial drug discovery.
• Contributes to NO homeostasis in bacteria and fungi, influencing biofilm and virulence.
• Helps explain how NO signaling is terminated in diverse organisms.
• Supports biotechnological applications for NO removal from industrial or biomedical settings.
• Is a target for understanding host-pathogen interactions and innate immunity.
• Informs the design of inhibitors that could potentiate NO-based therapies.
• Links to hemoglobin and myoglobin biochemistry through shared globin folds.
What Happens During nitric oxide dioxygenase [NAD(P)H] activity?
Substrate binding and oxygen activation
In simple terms: The enzyme first grabs oxygen and nitric oxide so they can react safely.
The catalytic cycle begins with binding of O2 to the ferrous heme iron of flavohemoglobin, forming a ferrous-oxy species. NO then binds to the distal pocket, and the B10 tyrosine hydroxyl is essential for stabilizing dioxygen and facilitating catalysis. This step ensures that NO is oxidized rather than released as a toxic radical.
NAD(P)H-dependent electron transfer
In simple terms: The enzyme uses NAD(P)H to supply electrons that keep the reaction going.
Flavohemoglobins contain an FAD domain that accepts electrons from NAD(P)H and transfers them via the heme to the catalytic site. This electron flow regenerates the ferrous heme after each turnover, allowing continuous NO oxidation. The reaction stoichiometry consumes one NAD(P)H per two NO molecules oxidized.
Nitrate formation and product release
In simple terms: Nitric oxide is converted into harmless nitrate, which leaves the enzyme.
The ferrous-oxy-NO intermediate rearranges to nitrate, which is released from the heme pocket. This step completes the detoxification of NO to nitrate, a stable and less reactive anion. The overall reaction is 2 NO + 2 O2 + NAD(P)H + H+ = 2 nitrate + NAD(P)+.
Inhibition and regulation by ligands
In simple terms: Molecules like carbon monoxide and some drugs can block the enzyme.
NO itself can inhibit the enzyme at high concentrations, and CO competes with O2 for the heme, reducing activity. Imidazole antibiotics also inhibit microbial flavohemoglobin, suggesting that this activity is a potential drug target. These regulatory features fine-tune NO detoxification under varying environmental conditions.
Key Genes Involved in GO:0008941 nitric oxide dioxygenase [NAD(P)H] activity
The following genes and proteins are directly implicated in nitric oxide dioxygenase [NAD(P)H] activity or its regulation across model organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| hmp (E. coli) | Flavohemoglobin with NOD activity | Model for NO detoxification and aerobic NO resistance |
| HbN (M. tuberculosis) | Hemoglobin with NOD activity | Enables survival in host macrophages by scavenging NO |
| glbN (Synechococcus) | Hemoglobin with NOD-like reactivity | Studied for heme attachment and NO reactivity |
| yhb1 (S. cerevisiae) | Flavohemoglobin | Fungal NO detoxification and nitrosative stress response |
| HMP (Bacillus subtilis) | Flavohemoglobin | Bacterial NO resistance and biofilm formation |
| VHb (Vitreoscilla) | Bacterial hemoglobin | Biotechnological NO scavenging and oxygen delivery |
| Ngb (Neuroglobin) | Globin with NOD-like activity | Neuroprotection and NO metabolism in neurons |
| Cygb (Cytoglobin) | Globin with NOD-like activity | Tissue protection against nitrosative stress |
| Mb (Myoglobin) | Oxygen storage globin | Model for heme reactivity and NO dioxygenation |
| Hb (Hemoglobin) | Oxygen transport globin | NO dioxygenase activity in red blood cells |
| FAD domain of flavohemoglobins | Electron transfer from NAD(P)H | Essential for catalytic turnover |
| B10 tyrosine (in globins) | Stabilizes dioxygen binding | Key residue for NOD catalysis |
| Distal lysine (in some hemoglobins) | Modulates ligand coordination | Affects NO reactivity and heme pocket dynamics |
| NAD(P)H dehydrogenase domain | Reduces FAD | Provides electrons for NO oxidation |
| Heme iron | Catalytic center | Binds O2 and NO for oxidation |
| FAD cofactor | Electron shuttle | Transfers electrons from NAD(P)H to heme |
| Flavohemoglobin reductase partner | Reduces flavohemoglobin | Regenerates active enzyme |
How Is nitric oxide dioxygenase [NAD(P)H] activity Regulated?
Nitric oxide dioxygenase activity is regulated at multiple levels. In bacteria, expression of flavohemoglobin genes such as hmp is induced by NO and nitrosative stress, often through transcriptional regulators like NsrR or Fnr. Enzyme activity is also controlled by substrate availability (O2 and NAD(P)H) and by product inhibition. Carbon monoxide and imidazole antibiotics inhibit the enzyme, indicating that small-molecule modulation is possible. In eukaryotes, globin expression and heme availability influence NOD activity, linking it to iron metabolism and redox signaling.
nitric oxide dioxygenase [NAD(P)H] activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| HbN (M. tuberculosis) | Tuberculosis pathogenesis and NO resistance | Knockout of hbN in M. tuberculosis; infection of macrophages |
| hmp (E. coli) | Bacterial NO detoxification and sepsis | hmp knockout and overexpression in E. coli; NO challenge |
| Ngb (Neuroglobin) | Neurodegeneration and stroke | Ngb knockout mice; neuronal NO stress models |
| Cygb (Cytoglobin) | Fibrosis and cancer | Cygb knockout mice; tissue injury models |
| Mb (Myoglobin) | Cardiomyopathy and exercise physiology | Mb knockout mice; cardiac NO stress |
Infectious disease and host-pathogen interactions
Mycobacterium tuberculosis HbN confers resistance to host-derived NO, supporting bacterial survival in macrophages. Inhibiting NOD activity could therefore sensitize pathogens to immune killing. This makes the enzyme a potential target for adjunctive antimicrobial therapy.
Neurodegeneration and NO toxicity
In the brain, excessive NO contributes to excitotoxicity and neurodegeneration. Globin-mediated NO dioxygenation may protect neurons by converting NO to nitrate. Dysregulation of this activity has been proposed to contribute to ischemic and neurodegenerative conditions.
Cardiovascular biology
Hemoglobin and myoglobin exhibit NO dioxygenase activity that modulates NO bioavailability in the vasculature. This activity influences blood flow, platelet function, and oxygen delivery. Understanding it may inform therapies for hypertension and ischemia-reperfusion injury.
From nitric oxide dioxygenase [NAD(P)H] activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of NOD activity increase NO sensitivity? | CRISPR knockout of hmp or hbN in bacteria |
| Which residues are required for catalysis? | Point mutations in B10 tyrosine or distal pocket residues |
| Can a human globin substitute for bacterial NOD? | Knock-in of human globin into bacterial NOD locus |
| Where is the enzyme localized? | Tagged knock-in with fluorescent protein |
| Does overexpression protect against nitrosative stress? | Overexpression of flavohemoglobin in mammalian cells |
| Can small molecules inhibit NOD? | Point-mutation models to test inhibitor binding |
How to Study the nitric oxide dioxygenase [NAD(P)H] activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Stopped-flow kinetics | NO consumption and nitrate formation rates | Determining catalytic efficiency and inhibition |
| NO electrode | Real-time NO concentration | Measuring NO scavenging by whole cells |
| CRISPR knockout | Loss of gene function | Testing requirement for NO resistance |
| Site-directed mutagenesis | Effect of point mutations | Identifying catalytic residues |
| X-ray crystallography | Three-dimensional structure | Visualizing heme pocket and ligand binding |
| Resonance Raman spectroscopy | Heme coordination and spin state | Probing ligand binding dynamics |
| RNA-seq | Transcriptional changes | Identifying NO-responsive regulons |
| Proteomics | Protein abundance and modifications | Detecting NOD enzyme expression |
Enzyme kinetics and NO consumption assays
Steady-state and transient kinetics using stopped-flow spectrophotometry measure NO consumption and nitrate production. These methods revealed the essential role of the B10 tyrosine in dioxygen binding. They also quantify inhibition by CO and imidazole antibiotics.
Genetic knockouts and complementation
Deleting NOD-encoding genes (e.g., hmp in E. coli) and testing growth under NO stress demonstrates the physiological role of the activity. Complementation with wild-type or mutant alleles identifies critical residues.
Structural biology and spectroscopy
X-ray crystallography and resonance Raman spectroscopy provide atomic-level views of heme coordination and ligand binding. These techniques show how covalent heme attachment or distal lysine coordination alters NO reactivity.
Transcriptomics and proteomics
RNA-seq and proteomics can identify genes co-regulated with NOD enzymes under nitrosative stress. Such studies reveal regulons controlled by NO-sensing transcription factors.
How CRISPR Can Be Used to Study GO:0008941 nitric oxide dioxygenase [NAD(P)H] activity
Knockout
CRISPR knockout of NOD-encoding genes such as hmp in E. coli or hbN in M. tuberculosis creates null mutants that are hypersensitive to NO. These models are used to test whether the enzyme is required for survival in host cells. They also serve as clean backgrounds for complementation studies.
Point Mutation
CRISPR-mediated point mutations can substitute catalytic residues like the B10 tyrosine or distal lysine. Such mutants reveal the precise contribution of individual side chains to dioxygen binding and NO oxidation. They are valuable for structure-function studies without altering protein expression levels.
Knock-in
Knock-in of epitope tags or fluorescent proteins at the endogenous NOD locus allows real-time localization and interaction studies. This approach preserves native regulation and can be used to track enzyme dynamics during infection. Knock-in of human globins into bacterial loci can test functional conservation.
Overexpression
CRISPR activation or cDNA overexpression of NOD enzymes increases NO detoxification capacity. Overexpression models are used to test whether enhanced NOD activity protects against nitrosative stress in mammalian cells or improves microbial survival. They also enable biochemical purification of the enzyme.
How EDITGENE Supports nitric oxide dioxygenase [NAD(P)H] activity Research
Researchers studying nitric oxide dioxygenase [NAD(P)H] activity-related genes often need to determine whether a candidate gene is causally involved in NO detoxification, host-pathogen interactions, or cellular stress responses. EDITGENE provides the full suite of CRISPR tools to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for nitric oxide dioxygenase [NAD(P)H] activity research.
Frequently Asked Questions About nitric oxide dioxygenase [NAD(P)H] activity
What is nitric oxide dioxygenase [NAD(P)H] activity?
It is a molecular function defined by GO:0008941 that catalyzes the reaction 2 NO + 2 O2 + NAD(P)H + H+ = 2 nitrate + NAD(P)+, detoxifying nitric oxide.
What genes are involved in nitric oxide dioxygenase [NAD(P)H] activity?
Key genes include hmp in E. coli, hbN in M. tuberculosis, and globin genes such as Ngb and Cygb in higher organisms.
What is the GO ID for nitric oxide dioxygenase [NAD(P)H] activity?
The GO ID is GO:0008941.
How does nitric oxide dioxygenase work?
It uses heme and FAD to bind O2 and NO, transferring electrons from NAD(P)H to oxidize NO to nitrate.
Why is nitric oxide dioxygenase important for bacteria?
It protects bacteria from host-derived NO, supporting survival in macrophages and other nitrosative environments.
What inhibits nitric oxide dioxygenase?
Carbon monoxide, high NO concentrations, and imidazole antibiotics inhibit the enzyme.
What is the role of the B10 tyrosine in NOD activity?
The B10 tyrosine hydroxyl is essential for dioxygen binding and catalysis in E. coli flavohemoglobin.
Can CRISPR be used to study nitric oxide dioxygenase?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study NOD genes.
What diseases are linked to nitric oxide dioxygenase?
It is linked to tuberculosis pathogenesis, neurodegeneration, and cardiovascular biology through NO metabolism.
How can I measure nitric oxide dioxygenase activity?
Common methods include stopped-flow kinetics, NO electrodes, and nitrate production assays.
Conclusion
GO:0008941 nitric oxide dioxygenase [NAD(P)H] activity is a fundamental enzymatic function that converts toxic nitric oxide to nitrate, protecting cells from nitrosative stress. Its study spans microbiology, immunology, and cardiovascular biology, with flavohemoglobins and related globins as key enzymes. CRISPR-based models now enable precise dissection of gene function and the development of inhibitors or enhancers for therapeutic applications.
References
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- 3. Pathania R et al.. 2002. Nitric oxide scavenging and detoxification by the Mycobacterium tuberculosis haemoglobin, HbN in Escherichia coli.. Mol Microbiol 45(5):1303-14 PMID: 12207698
- 4. Helmick RA et al.. 2005. Imidazole antibiotics inhibit the nitric oxide dioxygenase function of microbial flavohemoglobin.. Antimicrob Agents Chemother 49(5):1837-43 PMID: 15855504
- 5. Gardner AM et al.. 2002. Flavohemoglobin detoxifies nitric oxide in aerobic, but not anaerobic, Escherichia coli. Evidence for a novel inducible anaerobic nitric oxide-scavenging activity.. J Biol Chem 277(10):8166-71 PMID: 11751864
- 6. Preimesberger MR et al.. 2017. Covalent attachment of the heme to Synechococcus hemoglobin alters its reactivity toward nitric oxide.. J Inorg Biochem 177:171-182 PMID: 28968520
- 7. Gardner AM et al.. 2000. Steady-state and transient kinetics of Escherichia coli nitric-oxide dioxygenase (flavohemoglobin). The B10 tyrosine hydroxyl is essential for dioxygen binding and catalysis.. J Biol Chem 275(17):12581-9 PMID: 10777548
- 8. Martinez Grundman JE et al.. 2021. Control of distal lysine coordination in a monomeric hemoglobin: A role for heme peripheral interactions.. J Inorg Biochem 219:111437 PMID: 33892380
