This is a working overview of HPLC, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-04-12. Anything still debated is marked as such rather than presented as settled.
In humans, NAD+ can be synthesized from nicotinic acid, nicotinamide, nicotinamide riboside, and tryptophan through overlapping pathways. The salvage pathway recycles nicotinamide back to NAD+ and is often considered a major route in many tissues. Dietary precursors and intracellular recycling both contribute to the pool, but the quantitative importance of each source remains an active research question. NAD+ levels are not uniform across organs or cell compartments. Measurements in blood do not necessarily reflect concentrations inside tissues.
NAD+ is a dinucleotide composed of nicotinamide, ribose, and adenine linked by phosphate groups. Its full name is nicotinamide adenine dinucleotide, with "+" denoting the oxidized form. The molecule acts as a coenzyme in redox reactions, cycling between NAD+ and NADH. In cells, it participates in electron transfer during glycolysis, the citric acid cycle, and oxidative phosphorylation. It is distinct from NADP+, which carries an additional phosphate group and supports different biosynthetic reactions.
Beyond redox chemistry, NAD+ serves as a substrate for enzymes that transfer ADP-ribose or remove acetyl groups. Sirtuins, PARPs, and CD38-family enzymes consume NAD+ and produce nicotinamide and ADP-ribose-related products. These reactions link NAD+ availability to DNA repair, chromatin modification, and cellular signaling. Because the molecule is central to energy metabolism and regulation, changes in its concentration are studied in aging, immunity, and metabolic research. The balance between synthesis and consumption varies by tissue, developmental stage, and physiological state.
Stability studies show that NAD+ can hydrolyze under prolonged heat, extreme pH, or microbial contamination. Phosphate buffers near neutral pH are often used for short-term handling, though exact stability depends on concentration, temperature, and matrix. In biological samples, endogenous enzymes can rapidly degrade NAD+, making cold chain and fast processing important. Analytical reports should state extraction conditions, internal standards, and validation parameters. Without those details, comparisons across studies remain difficult and potentially misleading.
Laboratory measurement of NAD+ often begins with rapid quenching of cell or tissue samples to prevent enzymatic conversion. Acidic or alkaline extraction can precipitate proteins, but the chosen method affects recovery of oxidized and reduced forms. Enzymatic cycling assays provide high sensitivity by amplifying a NAD+-dependent reaction. High-performance liquid chromatography and mass spectrometry offer separation and structural confirmation. Each method has trade-offs in throughput, specificity, and the ability to distinguish NAD+ from close analogues.
Purified NAD+ is typically supplied as a white to off-white powder and stored desiccated at low temperature. Airtight containers limit moisture uptake, while protection from light reduces degradation of the nicotinamide ring. Aqueous stock solutions are less stable than solid material and are often aliquoted before freezing. Repeated freeze-thaw cycles can lower integrity, so working portions are kept separate. Purity is commonly checked by ultraviolet absorbance near 260 nm, high-performance liquid chromatography, or mass spectrometry.
| Property | Value | Notes |
|---|---|---|
| Common name | Nicotinamide adenine dinucleotide (oxidized) | Often shortened to NAD+ |
| Chemical class | Dinucleotide | Contains nicotinamide and adenine moieties |
| Molecular formula | C21H27N7O14P2 | Free acid form; charge depends on pH |
| Molar mass | About 663.43 g/mol | Calculated for C21H27N7O14P2 |
| CAS number | 53-84-9 | Common identifier for beta-NAD+ |
In redox reactions, NAD+ accepts a hydride ion, which consists of two electrons and one proton. The hydride adds to the nicotinamide ring at a specific carbon, converting NAD+ into NADH. Dehydrogenase enzymes use this step in glycolysis, the citric acid cycle, and fatty acid oxidation. NADH later donates electrons to the mitochondrial electron transport chain, helping to drive ATP synthesis. The balance between NAD+ and NADH reflects the metabolic state of a cell, and shifts in that balance can alter how pathways operate.
Beyond electron transfer, NAD+ serves as a substrate for enzymes that cleave it and attach its ADP-ribose portion to other molecules. This group includes poly(ADP-ribose) polymerases, CD38, and sirtuins. Such reactions consume NAD+ and can influence its availability for metabolism. Cells replenish NAD+ through a salvage pathway that recycles nicotinamide and through routes starting from tryptophan or vitamin B3 forms. How these synthesis and consumption routes are coordinated across tissues remains an active area of study, and compartment-specific concentrations are difficult to measure directly.
Nicotinamide adenine dinucleotide, abbreviated NAD+, is a dinucleotide built from adenine, nicotinamide, two ribose sugars, and two phosphate groups. The oxidized form carries a positive charge on the nicotinamide ring, while the reduced form, NADH, is neutral. This pair acts as a reversible electron carrier in cells. NAD+ is present in bacteria, plants, animals, and fungi. Its structure allows it to accept and donate electrons without being consumed in the reactions it supports.
Commercial NAD+ is available at research grade, often with purity specifications determined by high-performance liquid chromatography. Certificates of analysis may report water content, residual solvents, and counterion identity. Identity can be confirmed by ultraviolet absorbance near 260 nm, mass spectrometry, or enzymatic activity. Because different salt forms and hydration states exist, researchers should verify that the product matches the intended molecular form. Lot-to-lot variation in purity can affect quantitative assays and should be documented.
Solid NAD+ is usually supplied as a white to off-white powder or lyophilized preparation. It is hygroscopic and should be kept desiccated at low temperature, commonly -20 °C or below for long-term storage. Aqueous solutions are less stable than dry material and are often prepared fresh or stored frozen in aliquots. Light exposure and repeated freeze-thaw cycles can promote degradation, so amber containers and single-use aliquots are preferred. Buffered solutions near neutral pH are generally less stable than acidic or frozen preparations.
NAD+ also serves as a substrate for enzymes that cleave it, including sirtuins, PARPs, and CD38. These enzymes consume NAD+ and release nicotinamide and ADP-ribose or related products. The dual roles as redox cofactor and signaling substrate connect NAD+ to DNA repair, circadian regulation, and calcium signaling. Cellular NAD+ concentrations vary by tissue, time of day, and stress exposure. How these consumption pathways interact with redox balance remains an active area of research.
NAD+ is a dinucleotide composed of two nucleotides joined by a pyrophosphate linkage. One nucleotide contains adenine, and the other contains nicotinamide. The oxidized form carries a positive charge on the nicotinamide ring and is abbreviated NAD+. It functions as a cofactor in hydride-transfer reactions, accepting electrons in catabolic pathways. In cells, it interconverts with reduced NADH, forming a redox couple central to energy metabolism. The molecule is water-soluble and does not cross cell membranes freely without specific transport or precursor pathways.
Solid NAD+ is relatively stable when kept dry, cold, and protected from light. Aqueous solutions are more vulnerable to hydrolysis and can lose activity during repeated freeze-thaw cycles or prolonged storage at ambient temperature. Stability depends on pH, ionic strength, and the presence of degrading enzymes or metal ions. For many laboratory uses, aliquots are stored frozen and thawed only once. Exact degradation rates vary by matrix, so stability should be checked for each application rather than assumed.
Laboratory handling of NAD+ follows standard practices for hygroscopic fine chemicals. Personnel typically avoid inhalation and skin contact, use gloves and eye protection, and work in a ventilated area. Quality control may include ultraviolet absorbance at the nicotinamide maximum, chromatographic purity, water content, and identity confirmation by mass spectrometry. Because commercial preparations can contain counterions, residual solvents, or related nucleotides, a certificate of analysis helps verify the material. Researchers should confirm that the form supplied matches the intended assay.
Measuring NAD+ in biological samples requires care because the molecule is chemically reactive and present at low concentrations in some tissues. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and liquid chromatography coupled to mass spectrometry. Each method has different sensitivity and specificity, and sample preparation can affect results. Acidic or alkaline extraction steps are used in some protocols, but the choice depends on the analyte and matrix. No single method is universally optimal for every tissue or fluid.
A 15-hydroxyicosatetraenoate dehydrogenase metabolizes 15-hydroxyicosatetraenoic acid (i.e. 15(S)-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid or 15-HETE) to its 15-keto analog, 15-oxo-ETE, using NAD+ and NADH rather than NADP+ and NADPH as its co-factors. 15-Oxo-ETE appears to have a somewhat different spectrum of activities than its precursor, 15-HETE (see 15-Hydroxyicosatetraenoic acid
15-Oxo-ETE). Other eicosanoid oxoreductases that use NAD+ and NADH as co-factors include: 12-hydroxyicosatetraenoate dehydrogenase which metabolizes 12-hydroxyeicosatetraenoic acid (12-HETE) and LTB4 to their corresponding 12-oxo analogs and 11-hydroxy-TXB2 dehydrogenase, which metabolizes TXB2 to its 11-oxo analog; and 15-hydroxyprostaglandin dehydrogenase (NAD+) which metabolizes (5Z,13E)-(15S)-11alpha,15-dihydroxy-9-oxoprost-13-enoate to its 15-oxo analog. Other eicosanoid oxireductases that use NADP+ and NADPH as cofactors include LTB4 12-hydroxy dehydrogenase which metabolizes LTB4 to its 12-oxo analog, and 15-hydroxyprostaglandin-D dehydrogenase (NADP+), 15-hydroxyprostaglandin-I dehydrogenase (NADP+), and 15-hydroxyprostaglandin dehydrogenase (NADP+) which metabolize PGD2, PGI2, and (13E)-(15S)-11alpha,15-dihydroxy-9-oxoprost-13-enoate, respectively, to their corresponding 15-oxo analogs.
The strong tornado widened again and curved northward as it exited Hodonín and moved into a rural area, completely mowing down a large swath of trees as it impacted a patch of forest. Metal truss transmission towers were blown over in this area, crops were damaged in farm fields, and damage along this segment of the path was rated F2. The tornado briefly strengthened again one final time as it struck the village of Pánov at high-end F3 strength. Almost every structure in the small village was damaged in some way, and multiple homes were significantly damaged or destroyed, a few of which were leveled. Outbuildings were destroyed, cars were damaged by flying debris, and large trees were snapped and denuded as well. The tornado continued past Pánov and moved through another densely forested area, weakening back to F2 strength as it flattened another large swath of trees. The tornado continued to weaken, and trees beyond this point were downed at F1 intensity as the tornado continued to the northeast before it abruptly dissipated near Ratíškovice. In all, at least 1,200 buildings were damaged or destroyed by the tornado along its 27.1 kilometer (17 mi)-long path. 6 people were killed by the tornado, and at least 200 more were injured, some critically.
Cytochrome-b5 reductase is a NADH-dependent enzyme that converts ferricytochrome from a Fe3+ form to a Fe2+ form. It contains FAD and catalyzes the reaction: In its b5-reducing capacity, this enzyme is involved in desaturation and elongation of fatty acids, cholesterol biosynthesis, and drug metabolism. This enzyme can also reduce methemoglobin to normal hemoglobin, gaining it the inaccurate synonym methemoglobin reductase. Isoforms expressed in erythrocytes (CYB5R1, CYB5R3) perform this function in vivo. Ferricyanide is another substrate in vitro.
The protein encoded by the DLD gene comes together with another protein to form a dimer in the central metabolic pathway. Several amino acids within the catalytic pocket have been identified as important to DLD function, including R281 and N473. Although the overall fold of the human enzyme is similar to that of yeast, the human structure is different in that it has two loops that extend from the general protein structure and into the FAD binding sites when bound the NAD+ molecule, required for catalysis, is not close to the FAD moiety. However, when NADH is bound instead, it is stacked directly op top of the FAD central structure. The current hE3 structures show directly that the disease-causing mutations occur at three locations in the human enzyme: the dimer interface, the active site, and the FAD and NAD(+)-binding sites.
Sources: en.wikipedia.org
The first step in the NADP-ME type C4 pathway is the conversion of pyruvate (Pyr) to phosphoenolpyruvate (PEP), by the enzyme Pyruvate phosphate dikinase (PPDK). This reaction requires inorganic phosphate and ATP plus pyruvate, producing PEP, AMP, and inorganic pyrophosphate (PPi). The next step is the carboxylation of PEP by the PEP carboxylase enzyme (PEPC) producing oxaloacetate. Both of these steps occur in the mesophyll cells: pyruvate + Pi + ATP → PEP + AMP + PPi PEP + CO2 → oxaloacetate PEPC has a low KM for HCO−3 — and, hence, high affinity, and is not confounded by O2 thus it will work even at low concentrations of CO2. The product is usually converted to malate (M), which diffuses to the bundle-sheath cells surrounding a nearby vein. Here, it is decarboxylated by the NADP-malic enzyme (NADP-ME) to produce CO2 and pyruvate. The CO2 is fixed by RuBisCo to produce phosphoglycerate (PGA) while the pyruvate is transported back to the mesophyll cell, together with about half of the phosphoglycerate (PGA). This PGA is chemically reduced in the mesophyll and diffuses back to the bundle sheath where it enters the conversion phase of the Calvin cycle. For each CO2 molecule exported to the bundle sheath the malate shuttle transfers two electrons, and therefore reduces the demand of reducing power in the bundle sheath.
The strong tornado widened again and curved northward as it exited Hodonín and moved into a rural area, completely mowing down a large swath of trees as it impacted a patch of forest. Metal truss transmission towers were blown over in this area, crops were damaged in farm fields, and damage along this segment of the path was rated F2. The tornado briefly strengthened again one final time as it struck the village of Pánov at high-end F3 strength. Almost every structure in the small village was damaged in some way, and multiple homes were significantly damaged or destroyed, a few of which were leveled. Outbuildings were destroyed, cars were damaged by flying debris, and large trees were snapped and denuded as well. The tornado continued past Pánov and moved through another densely forested area, weakening back to F2 strength as it flattened another large swath of trees. The tornado continued to weaken, and trees beyond this point were downed at F1 intensity as the tornado continued to the northeast before it abruptly dissipated near Ratíškovice. In all, at least 1,200 buildings were damaged or destroyed by the tornado along its 27.1 kilometer (17 mi)-long path. 6 people were killed by the tornado, and at least 200 more were injured, some critically.
Cytochrome-b5 reductase is a NADH-dependent enzyme that converts ferricytochrome from a Fe3+ form to a Fe2+ form. It contains FAD and catalyzes the reaction: In its b5-reducing capacity, this enzyme is involved in desaturation and elongation of fatty acids, cholesterol biosynthesis, and drug metabolism. This enzyme can also reduce methemoglobin to normal hemoglobin, gaining it the inaccurate synonym methemoglobin reductase. Isoforms expressed in erythrocytes (CYB5R1, CYB5R3) perform this function in vivo. Ferricyanide is another substrate in vitro.
Clostridioides difficile has a highly diverse epigenome, with 17 high-quality methylation motifs reported so far, the majority pertaining to the 6mA type. Methylation at one of these motifs - CAAAAA, was shown to impact sporulation, a key step in C. difficile disease transmission, as well as cell length, biofilm formation, and host colonization. At least eight mainly temperate bacteriophages have been isolated from C. difficile, ranging in genome size from about 30 to about 60 kbp. Both environmentally and clinically derived C. difficile strains carry a diverse and prevalent set of prophages. Canada Pathogen Safety Data Sheets: Infectious Substances – Clostridium difficile, Public Health Agency, Canada, September 10, 2014. Type strain of Clostridium difficile, BacDive—the Bacterial Diversity Metadatabase
Sources: en.wikipedia.org
5-Hydroxyeicosanoid dehydrogenase (5-HEDH) or more formally, nicotinamide adenine dinucleotide phosphate (NADP+)-dependent dehydrogenase, is an enzyme that metabolizes between two eicosanoid metabolites of arachidonate 5-lipoxygenase (5-LOX): 5-hydroxyeicosatetraenoic acid (5-(S)-HETE), and its 5-keto analog 5-oxo-eicosatetraenoic acid (5-oxo-ETE). It also acts in the reverse direction, metabolizing 5-oxo-ETE to 5(S)-HETE. Since 5-oxo-ETE is 30–100-fold more potent than 5(S)-HETE in stimulating various cell types, 5-HEDH is regarded as a regulator and promoter of the influence that 5-LOX and its metabolites have on cell function. Although 5-HEDH has been evaluated in a wide range of intact cells and in crude microsome preparations, it has not yet been evaluated for its structure or gene, and most studies on it have been limited to human tissues.
A 15-hydroxyicosatetraenoate dehydrogenase metabolizes 15-hydroxyicosatetraenoic acid (i.e. 15(S)-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid or 15-HETE) to its 15-keto analog, 15-oxo-ETE, using NAD+ and NADH rather than NADP+ and NADPH as its co-factors. 15-Oxo-ETE appears to have a somewhat different spectrum of activities than its precursor, 15-HETE (see 15-Hydroxyicosatetraenoic acid
CYB5R1, NADH-cytochrome b5 reductase 1, located on chromosome 1q32.1 with 9 exons that encode for c5br. CYB5R2, NADH-cytochrome b5 reductase 2, located on chromosome 11p15.4 with 12 exons that encode for c5br. CYB5R3, NADH-cytochrome b5 reductase 3, located on chromosome 22q13.2 with 12 exons that encode for c5br. CYB5R4, NADH-cytochrome b5 reductase 4, located on chromosome 6q14.2 with 16 exons that encode for c5br. Mutations in cytochrome b5 reductase can lead to many disorders, including autosomal recessive congenital methemoglobinemia. There are over 65 mutations of the enzyme that can lead to various types of the disorder. Some include:
5-HEDH is an NADPH dehydrogenase oxidoreductase enzyme. It transfers a hydrogen cation (or hydron) H+ from 5(S)-hydroxy (i.e. 5(S)-OH) residues of its fatty acid targets to nicotinamide adenine dinucleotide phosphate+ (NADP+) to form 5-oxo (i.e. 5-O=) counterparts of its targets plus reduced NADP+, i.e. NADPH. The reaction (where R indicates a long chain [14 or more carbons] fatty acid) is: NADP+ + 5(S)-hydroxy fatty acid (i.e. 5(S)-OH-R) ⇌ {\displaystyle \rightleftharpoons } NADPH + H+ + oxo fatty acid (i.e. 5-O=R) The reaction appears to follow a ping-pong mechanism. It is fully reversible, readily converting 5-oxo targets to their corresponding 5(S)-hydroxy counterparts. The direction of this reaction is dependent on the level of NADP+ relative to that of NADPH: The immediate metabolic precursor to 5(S)-HETE, 5(S)-hydroperoxy-6S,8Z,11Z,14Z-eicosatetraenoic acid 5(S)-HpETE, can be converted to 5-oxo-ETE in a non-enzymatic dehydration reaction or chemical lipid peroxidation reactions. The physiological occurrence and relevancy of these reaction pathways has not been ascertained.
In the evening hours of 24 June 2021, a rare, violent, and deadly long-tracked tornado struck several villages in the Hodonín and Břeclav districts of the South Moravian Region of the Czech Republic, killing six people and injuring 576 others. This tornado is the widest on record in Europe, at 3.5 kilometres (2.2 mi) maximum width. The tornado struck seven municipalities, with the worst damage in the villages of Hrušky, Moravská Nová Ves, Mikulčice and Lužice. This tornado was the strongest ever documented in modern Czech history and the deadliest European tornado since 2001. It was rated as an F4 on the Fujita scale and an IF4 on the International Fujita scale. This made it the first confirmed violent (IF4+) tornado in Europe since June 2017, when an IF4 tornado struck the village of Maloye Pes'yanovo in Russia, until the 2026 Ayyasha-Çaybeyi-Akçamezra tornado on May 3rd 2026, it was the only IF4 rated tornado to occur since the scale was introduced.
Sources: en.wikipedia.org
The plus sign indicates the oxidized form of nicotinamide adenine dinucleotide, which can accept electrons. When it accepts electrons, it becomes NADH. The two forms together support redox reactions in cells.
No. NAD+ is the oxidized form and NADH is the reduced form. They differ by two electrons and a proton equivalent, and cells interconvert them during metabolism.
Yes. NAD+ is present in all living cells and is required for fundamental metabolic reactions. Its concentration varies by tissue, compartment, and time.
Many enzymes consume or produce NAD+ within seconds after a sample is collected. Quenching stops those reactions and helps preserve the ratio between oxidized and reduced forms. The exact quenching method depends on the tissue or cell type and the analytes of interest.