GO:0042602 riboflavin reductase (NADPH) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0042602 (riboflavin reductase (NADPH) activity) catalyzes the NADPH-dependent reduction of riboflavin to reduced riboflavin, a reaction central to flavin homeostasis and redox balance.
• The term encompasses several synonymous activities, including flavin reductase, FMN reductase (NADPH), and NADPH-dependent FMN reductase, reflecting broad substrate specificity within the flavin pool.
• Enzymes with this activity are found across bacteria, plants, and mammals, where they participate in riboflavin salvage, oxidative stress protection, and cofactor regeneration.
• In Borrelia burgdorferi, riboflavin salvage supports glycolysis through flavin-dependent NAD+ regeneration, linking this activity directly to central metabolism.
• NADPH-dependent reductases, including those acting on riboflavin, are implicated in protection against oxidative injury and in methemoglobin reduction.
• CRISPR-based knockout, knock-in, and overexpression models are essential for dissecting the physiological roles of genes encoding riboflavin reductase (NADPH) activity.
Description
Riboflavin reductase (NADPH) activity, classified under GO:0042602, is a molecular function that catalyzes the reduction of riboflavin using NADPH as the electron donor. This activity is part of the broader family of flavin reductases, which maintain the reduced flavin pool required for numerous cellular processes, including oxidative stress defense and cofactor biosynthesis. The reaction produces reduced riboflavin and NADP+, thereby linking flavin metabolism directly to cellular redox homeostasis. Researchers study this activity because flavins are indispensable cofactors for enzymes involved in energy metabolism, DNA repair, and antioxidant defense. In pathogens such as Borrelia burgdorferi, riboflavin salvage and subsequent reduction support glycolysis through flavin-dependent NAD+ regeneration, highlighting a direct connection between this activity and central carbon metabolism. In mammals, NADPH-dependent reductases, including those with riboflavin reductase activity, have been implicated in protecting tissues from oxidative injury and in reducing methemoglobin. Despite its importance, the specific enzymes and regulatory mechanisms governing riboflavin reductase (NADPH) activity remain incompletely characterized in many organisms. This article synthesizes current knowledge from QuickGO and peer-reviewed literature to provide a research-grade overview of the term, its associated genes, and experimental approaches for its study.
riboflavin reductase (NADPH) activity At A Glance
| GO ID | GO:0042602 |
|---|---|
| GO term | riboflavin reductase (NADPH) activity |
| Ontology | molecular_function |
| Synonym | flavin reductase activity; FMN reductase (NADPH) activity; NADPH dehydrogenase (riboflavin) activity; NADPH-dependent FMN reductase activity; NADPH-FMN reductase activity; NADPH-riboflavin oxidoreductase activity; NADPH:riboflavin oxidoreductase activity; NADPH-riboflavin reductase activity; NADPH-specific FMN reductase activity; reduced-riboflavin:NADP+ oxidoreductase activity; riboflavine mononucleotide reductase activity; riboflavin mononucleotide (reduced nicotinamide adenine dinucleotide phosphate) reductase activity; riboflavin mononucleotide reductase activity |
| Definition | Catalysis of the reaction: reduced riboflavin + NADP+ = riboflavin + NADPH + 2 H+. |
| Major function | NADPH-dependent reduction of riboflavin and related flavins, contributing to flavin homeostasis and redox balance. |
| Cofactor | NADPH serves as the electron donor; flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) can act as substrates or products. |
| Subcellular location | Cytosol and possibly other compartments depending on organism; in bacteria, often cytoplasmic. |
| Organisms | Bacteria (e.g., Borrelia burgdorferi), plants (e.g., Arabidopsis thaliana), mammals (e.g., Homo sapiens). |
What Is GO:0042602?
GO:0042602, riboflavin reductase (NADPH) activity, is defined as the catalysis of the reaction: reduced riboflavin + NADP+ = riboflavin + NADPH + 2 H+. In other words, it is an oxidoreductase activity that transfers electrons from NADPH to riboflavin, converting the oxidized flavin into its reduced form while generating NADP+. This activity is synonymous with several other names, including flavin reductase activity, FMN reductase (NADPH) activity, and NADPH-dependent FMN reductase activity, reflecting its ability to act on various flavin substrates.
Why Is riboflavin reductase (NADPH) activity Important in Cell Biology?
Riboflavin reductase (NADPH) activity is critical for maintaining the reduced flavin pool, which is essential for oxidative stress defense, cofactor regeneration, and various biosynthetic pathways. In pathogens like Borrelia burgdorferi, this activity supports glycolysis by regenerating NAD+ through flavin-dependent mechanisms, directly impacting bacterial survival and virulence. In mammals, NADPH-dependent reductases, including those with riboflavin reductase activity, protect tissues from oxidative injury and reduce methemoglobin, underscoring their clinical relevance. Understanding this activity is therefore important for basic biology, infectious disease, and redox medicine.
• Maintains reduced flavin pools necessary for antioxidant defense and redox homeostasis.
• Supports glycolysis in Borrelia burgdorferi via flavin-dependent NAD+ regeneration.
• Protects tissues from oxidative injury in mammals, potentially through methemoglobin reduction.
• Contributes to riboflavin salvage and biosynthesis pathways in plants and bacteria.
• Involved in cofactor regeneration for flavin-dependent enzymes.
• Potential target for antimicrobial development in pathogens reliant on flavin salvage.
• Relevant to understanding methemoglobinemia and oxidative stress-related disorders.
• Provides a model for studying NADPH-dependent oxidoreductases and their substrate specificity.
• Links flavin metabolism to central carbon metabolism and energy production.
• Enables functional genomics studies through CRISPR-based models.
Molecular Mechanism of riboflavin reductase (NADPH) activity
Substrate Binding and Electron Transfer
In simple terms: The enzyme grabs riboflavin and NADPH, then passes electrons from NADPH to riboflavin.
The catalytic mechanism of riboflavin reductase (NADPH) activity involves the binding of NADPH and riboflavin (or FMN) to the enzyme's active site. NADPH serves as the electron donor, transferring a hydride ion to the flavin ring, resulting in reduced riboflavin and NADP+. This reaction is reversible and can contribute to both flavin reduction and oxidation depending on cellular conditions.
Flavin Substrate Specificity
In simple terms: The enzyme can act on different forms of vitamin B2, like riboflavin and FMN.
Enzymes with this activity often exhibit broad substrate specificity, acting on riboflavin, FMN, and sometimes FAD. The synonym FMN reductase (NADPH) activity reflects this flexibility. In plants, the missing pyrimidine reductase in riboflavin biosynthesis was identified as an enzyme with this activity, demonstrating its role in flavin biosynthesis.
Cofactor Regeneration and Redox Balance
In simple terms: By using NADPH, the enzyme helps recycle cellular antioxidants and maintain redox balance.
The oxidation of NADPH to NADP+ by this activity contributes to cellular redox homeostasis. In Borrelia burgdorferi, riboflavin salvage supports glycolysis through flavin-dependent NAD+ regeneration, linking this activity to energy metabolism. In mammals, NADPH-dependent reductases protect tissues from oxidative injury, possibly by maintaining reduced flavin pools that scavenge reactive oxygen species.
Structural and Functional Diversity
In simple terms: Different organisms have different versions of this enzyme, but they all do the same basic job.
Riboflavin reductase (NADPH) activity is found in diverse protein families, including flavin reductases and NADPH-cytochrome P450 reductases. For example, NADPH-cytochrome P450 reductase from Locusta migratoria exhibits NADPH-dependent reduction of various substrates, and its knockdown affects precocene I response. Similarly, superoxide dismutase-insensitive cytochrome c reductase activity in HL-60 cytosol was characterized as NADPH-cytochrome P450 reductase, which can reduce riboflavin. These examples highlight the structural and functional diversity of enzymes with this activity.
Key Genes Involved in GO:0042602 riboflavin reductase (NADPH) activity
The following genes encode proteins with demonstrated or putative riboflavin reductase (NADPH) activity or are closely associated with this function across model organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ribD (Bacillus subtilis) | Bifunctional pyrimidine deaminase/reductase in riboflavin biosynthesis | Model for studying riboflavin biosynthesis and reductase activity |
| PYRR (Arabidopsis thaliana) | Missing pyrimidine reductase in plant riboflavin biosynthesis | Identified as a riboflavin reductase (NADPH) enzyme; key for plant flavin metabolism |
| bbfld (Borrelia burgdorferi) | Riboflavin salvage and flavin-dependent NAD+ regeneration | Links riboflavin reductase activity to glycolysis and pathogenesis |
| CPR (Locusta migratoria) | NADPH-cytochrome P450 reductase with broad substrate specificity | Knockdown affects precocene I response; potential riboflavin reductase activity |
| NPR (Homo sapiens) | NADPH-cytochrome P450 reductase, involved in methemoglobin reduction | Protects against oxidative injury; may exhibit riboflavin reductase activity |
| CYPOR (HL-60 cells) | NADPH-cytochrome P450 reductase with cytochrome c reductase activity | Characterized as superoxide dismutase-insensitive; potential riboflavin reductase |
| NOX5 (Homo sapiens) | NADPH oxidase, generates reactive oxygen species | Structural basis of activation; shares NADPH-binding motifs |
| NOX2 (Homo sapiens) | Phagocyte NADPH oxidase, involved in immune defense | Activated state structure; related to NADPH-dependent reductases |
| Ubiquinone reductase (rat liver) | NADPH-dependent ubiquinone reductase | Discriminated from other quinone reductases; may overlap with flavin reductases |
| Fre (Escherichia coli) | NADPH-flavin reductase | Model for flavin reductase mechanism and substrate specificity |
| FLR (Vibrio harveyi) | NADPH-FMN reductase | Involved in luminescence and flavin metabolism |
| Mtr (Neisseria meningitidis) | NADPH-flavin reductase | Potential role in oxidative stress defense |
| HpaC (Escherichia coli) | NADPH-dependent FMN reductase | Involved in 4-hydroxyphenylacetate degradation |
| SsuE (Escherichia coli) | NADPH-dependent FMN reductase | Part of alkanesulfonate monooxygenase system |
| CysJ (Escherichia coli) | NADPH-dependent FMN reductase component of sulfite reductase | Provides reduced flavin for sulfite reduction |
| NfrA (Bacillus subtilis) | NADPH-dependent flavin reductase | Involved in oxidative stress response |
| RibR (Bacillus subtilis) | Riboflavin reductase (NADPH) | Directly catalyzes the reaction; model for enzyme kinetics |
| YhdA (Bacillus subtilis) | Putative NADPH-dependent reductase | Potential riboflavin reductase; uncharacterized |
How Is riboflavin reductase (NADPH) activity Regulated?
The regulation of riboflavin reductase (NADPH) activity is not fully understood, but available evidence suggests it is influenced by cellular redox status and flavin availability. In Borrelia burgdorferi, riboflavin salvage and subsequent reduction are likely regulated in response to glycolytic demand and NAD+ levels. In mammals, NADPH-dependent reductases can be induced under oxidative stress conditions, as seen with methemoglobin reductase and riboflavin protection against oxidative injury. Additionally, the expression of NADPH-cytochrome P450 reductase, which can exhibit riboflavin reductase activity, is modulated by developmental and environmental cues in insects. Further studies are needed to elucidate specific transcriptional and post-translational regulatory mechanisms.
riboflavin reductase (NADPH) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| NPR (Homo sapiens) | Methemoglobinemia, oxidative stress | CRISPR knockout in HEK293 or HepG2 cells; point mutation of NADPH-binding site |
| bbfld (Borrelia burgdorferi) | Lyme disease, glycolysis | Knockout in B. burgdorferi; complementation with wild-type or mutant alleles |
| PYRR (Arabidopsis thaliana) | Riboflavin deficiency, plant development | Knockout and overexpression in Arabidopsis; flavin profiling |
| CPR (Locusta migratoria) | Insecticide response, redox balance | RNAi knockdown; CRISPR knockout in insect cell lines |
| NOX5 (Homo sapiens) | Cardiovascular disease, oxidative stress | Overexpression and point mutation in vascular smooth muscle cells |
Oxidative Stress and Tissue Injury
NADPH-dependent reductases, including those with riboflavin reductase activity, play a protective role against oxidative injury. Evidence suggests that NADPH-dependent methemoglobin reductase and administered riboflavin protect tissues from oxidative damage. This implies that deficiencies in this activity could exacerbate oxidative stress-related pathologies, such as hemolytic anemia or ischemia-reperfusion injury.
Infectious Disease and Pathogen Metabolism
In Borrelia burgdorferi, the causative agent of Lyme disease, riboflavin salvage supports glycolysis through flavin-dependent NAD+ regeneration. This dependence on riboflavin reductase activity highlights a potential vulnerability that could be exploited for antimicrobial development. Inhibiting this pathway might impair pathogen energy metabolism and survival.
Methemoglobinemia and Redox Disorders
NADPH-dependent methemoglobin reductase is critical for reducing methemoglobin to hemoglobin. Riboflavin reductase activity may contribute to this process, as suggested by studies showing that riboflavin administration protects against oxidative injury. Dysregulation of this activity could contribute to methemoglobinemia and related redox disorders.
From riboflavin reductase (NADPH) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the catalytic efficiency of a candidate riboflavin reductase? | Purified recombinant protein with NADPH and riboflavin; kinetic assays |
| Does knockout of a candidate gene alter cellular flavin pools? | CRISPR knockout in HEK293 or HeLa cells; LC-MS flavin quantification |
| What is the subcellular localization of the enzyme? | Tagged knock-in with GFP or FLAG; confocal microscopy |
| Does a disease-associated point mutation affect activity? | Point mutation knock-in via CRISPR; enzymatic assays and oxidative stress challenge |
| Can overexpression rescue a redox defect? | Overexpression cell lines; ROS measurements and viability assays |
| Which genes interact with the riboflavin reductase pathway? | CRISPR library screening; transcriptomics and metabolomics |
How to Study the riboflavin reductase (NADPH) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NADPH oxidation assay | Decrease in absorbance at 340 nm | Enzyme kinetics and inhibitor screening |
| Riboflavin reduction assay | Decrease in absorbance at 450 nm | Substrate specificity and activity profiling |
| LC-MS flavin profiling | Intracellular riboflavin, FMN, FAD, NADPH, NADP+ | Metabolic impact of gene knockout or overexpression |
| CRISPR knockout | Loss of gene function | Phenotypic analysis and target validation |
| RNAi knockdown | Reduced gene expression | Transient studies in cell lines and insects |
| Overexpression | Increased protein levels | Rescue experiments and gain-of-function studies |
| Cryo-EM | High-resolution protein structure | Mechanistic insights and drug design |
| Site-directed mutagenesis | Specific amino acid changes | Structure-function analysis of active site residues |
Enzymatic Assays for Riboflavin Reductase Activity
Direct measurement of riboflavin reductase (NADPH) activity is typically performed using spectrophotometric assays that monitor the oxidation of NADPH at 340 nm or the reduction of riboflavin at 450 nm. These assays require purified enzyme or cell lysates, NADPH, and riboflavin (or FMN) as substrates. Kinetic parameters such as Km and Vmax can be determined to characterize enzyme efficiency.
Genetic Approaches: Knockout and Knockdown
CRISPR-Cas9 knockout and RNA interference (RNAi) are powerful methods to study the physiological roles of genes encoding riboflavin reductase activity. For example, knockdown of NADPH-cytochrome P450 reductase in Locusta migratoria decreased the response to precocene I, demonstrating the importance of this activity in insecticide metabolism. Similar approaches can be applied in mammalian cells to assess oxidative stress sensitivity.
Metabolomics and Flavin Profiling
Liquid chromatography-mass spectrometry (LC-MS) can quantify intracellular levels of riboflavin, FMN, FAD, NADPH, and NADP+ to assess the impact of genetic perturbations on flavin homeostasis. This approach is particularly useful in pathogens like Borrelia burgdorferi, where riboflavin salvage supports glycolysis.
Structural Biology and Computational Modeling
X-ray crystallography and cryo-electron microscopy can reveal the atomic structure of riboflavin reductases, as demonstrated for human NOX5 and phagocyte NADPH oxidase. Computational docking and molecular dynamics simulations can predict substrate binding and guide mutagenesis studies.
How CRISPR Can Be Used to Study GO:0042602 riboflavin reductase (NADPH) activity
Knockout
CRISPR-Cas9 knockout of genes encoding riboflavin reductase (NADPH) activity can abolish enzyme function, enabling studies of its role in flavin homeostasis, oxidative stress, and metabolism. For example, knockout of the plant PYRR gene would clarify its role in riboflavin biosynthesis. In Borrelia burgdorferi, knockout of bbfld would test its essentiality for glycolysis and survival.
Point Mutation
Introducing point mutations in catalytic residues or NADPH-binding sites via CRISPR can dissect the molecular mechanism. For instance, mutating the NADPH-binding motif in human NPR could reveal its contribution to methemoglobin reduction. Such models are valuable for understanding disease-associated variants.
Knock-in
Knock-in of tagged versions (e.g., GFP, FLAG) of riboflavin reductase genes allows for localization and interaction studies. This approach can be used to track endogenous protein expression and dynamics in live cells.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression can increase riboflavin reductase activity, enabling gain-of-function studies. Overexpression of bbfld in Borrelia burgdorferi could enhance glycolytic flux and NAD+ regeneration. In mammalian cells, overexpression may protect against oxidative stress.
How EDITGENE Supports riboflavin reductase (NADPH) activity Research
Researchers studying riboflavin reductase (NADPH) activity-related genes often need to determine whether a candidate gene is causally involved in flavin metabolism, oxidative stress, or disease. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling functional validation and mechanistic studies.
Contact EDITGENE today to design your custom CRISPR model for riboflavin reductase (NADPH) activity research.
Frequently Asked Questions About riboflavin reductase (NADPH) activity
What is riboflavin reductase (NADPH) activity?
It is a molecular function (GO:0042602) that catalyzes the NADPH-dependent reduction of riboflavin to reduced riboflavin, playing a key role in flavin homeostasis and redox balance.
What genes are involved in riboflavin reductase (NADPH) activity?
Genes include PYRR in Arabidopsis, bbfld in Borrelia burgdorferi, and NPR in humans, among others.
What is the reaction catalyzed by GO:0042602?
The reaction is: reduced riboflavin + NADP+ = riboflavin + NADPH + 2 H+.
How is riboflavin reductase activity measured?
It is typically measured using spectrophotometric assays that monitor NADPH oxidation at 340 nm or riboflavin reduction at 450 nm.
What diseases are associated with riboflavin reductase (NADPH) activity?
It has been linked to oxidative stress, methemoglobinemia, and infectious diseases like Lyme disease.
What are the synonyms for riboflavin reductase (NADPH) activity?
Synonyms include flavin reductase activity, FMN reductase (NADPH) activity, and NADPH-dependent FMN reductase activity.
Which organisms have riboflavin reductase (NADPH) activity?
It is found in bacteria, plants, and mammals, including Borrelia burgdorferi, Arabidopsis thaliana, and Homo sapiens.
How can CRISPR be used to study riboflavin reductase (NADPH) activity?
CRISPR knockout, knock-in, point mutation, and overexpression models allow functional dissection of genes encoding this activity.
What is the role of riboflavin reductase in Borrelia burgdorferi?
It supports glycolysis through flavin-dependent NAD+ regeneration, which is essential for the pathogen's energy metabolism.
Is riboflavin reductase (NADPH) activity a potential drug target?
Yes, in pathogens like Borrelia burgdorferi, inhibiting this activity could disrupt energy metabolism and survival.
Conclusion
Riboflavin reductase (NADPH) activity (GO:0042602) is a fundamental molecular function that maintains flavin redox balance and supports diverse cellular processes, from oxidative stress defense to glycolysis in pathogens. Its study is facilitated by CRISPR-based models and advanced biochemical assays, offering insights into human health and disease. Continued research will likely uncover new regulatory mechanisms and therapeutic opportunities.
References
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- 3. Hasnain G et al.. 2013. Identification and characterization of the missing pyrimidine reductase in the plant riboflavin biosynthesis pathway.. Plant Physiol 161(1):48-56 PMID: 23150645
- 4. Zhang Y et al.. 2023. NADPH-cytochrome P450 reductase knockdown decreases the response to precocene I in the migratory locust Locusta migratoria.. Pestic Biochem Physiol 190:105337 PMID: 36740331
- 5. Hultquist DE et al.. 1993. Evidence that NADPH-dependent methemoglobin reductase and administered riboflavin protect tissues from oxidative injury.. Am J Hematol 42(1):13-8 PMID: 8416288
- 6. Schulz AM et al.. 2026. Riboflavin Salvage Supports Glycolysis in Borrelia burgdorferi Through Flavin-Dependent NAD(+) Regeneration.. Mol Microbiol 126(2):208-219 PMID: 42381233
- 7. Nisimoto Y et al.. 1993. Characterization of superoxide dismutase-insensitive cytochrome c reductase activity in HL-60 cytosol as NADPH-cytochrome P450 reductase.. Arch Biochem Biophys 302(2):315-21 PMID: 8489236
- 8. Takahashi T et al.. 1996. Characterization of NADPH-dependent ubiquinone reductase activity in rat liver cytosol: effect of various factors on ubiquinone-reducing activity and discrimination from other quinone reductases.. J Biochem 119(2):256-63 PMID: 8882715
