This is a working overview of LC-MS, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-09-15 and is reviewed periodically as new material appears.
Laboratory measurement of NAD+ usually begins with rapid sample quenching because the molecule can change form after collection. Enzymatic cycling assays amplify signal through coupled reactions and are suited to small samples. High-performance liquid chromatography with ultraviolet detection separates NAD+ from related nucleotides. Liquid chromatography-mass spectrometry offers higher specificity and can distinguish NAD+ from close analogs. Each method has trade-offs in sensitivity, throughput, and equipment needs, so reported values depend heavily on extraction and detection choices.
Stability of NAD+ depends on form, temperature, pH, and water content. The solid is generally more stable than solutions, and it should be kept dry and cold. In solution, hydrolysis can cleave the dinucleotide, especially under alkaline conditions or at elevated temperature. Light exposure may also contribute to degradation. Buffers, chelating agents, and sterile handling can reduce losses, but no single condition preserves all preparations indefinitely. Researchers often prepare working solutions shortly before use and verify activity or purity after storage.
NAD+ stands for nicotinamide adenine dinucleotide, the oxidized form of a coenzyme found in all living cells. The molecule consists of two nucleotides, adenine and nicotinamide ribose, joined through phosphate groups. Its chemical formula is C21H27N7O14P2, and the free acid has a molar mass near 663.43 grams per mole. In redox reactions, NAD+ accepts a hydride ion and becomes NADH. The pair NAD+ and NADH participates in hundreds of metabolic reactions, including steps in glycolysis, the citric acid cycle, and oxidative phosphorylation.
In cells, NAD+ functions primarily as an electron carrier. Dehydrogenase enzymes in glycolysis and the citric acid cycle transfer hydride from substrates to NAD+, producing NADH. NADH then delivers electrons to the mitochondrial respiratory chain, supporting ATP synthesis. In fermentation, NADH is reoxidized to NAD+ so that glycolysis can continue. The balance between NAD+ and NADH helps set metabolic flux. Beyond redox, NAD+ serves as a substrate for enzymes that cleave it, including sirtuins, poly(ADP-ribose) polymerases, and CD38. These reactions consume NAD+ and release nicotinamide and ADP-ribose products.
Biosynthesis occurs through salvage, Preiss-Handler, and de novo pathways. In mammals, the salvage pathway from nicotinamide predominates, and NAMPT is often described as rate-limiting. Nicotinamide riboside and nicotinic acid enter related routes that converge on NAD+ production. Tissue NAD+ concentrations vary widely and are maintained by a balance of synthesis and consumption. Some studies report age-related declines in certain tissues, but whether these changes cause disease or can be reversed to improve human health remains an open question.
| Property | Value | Notes |
|---|---|---|
| CAS number | 53-84-9 | Refers to the free acid form of NAD+. |
| Molecular formula | C21H27N7O14P2 | Free acid; salts include additional counterions. |
| UV absorbance maximum | 259-260 nm | Used for detection and concentration estimation. |
| Typical storage | -20 °C or below, desiccated | Protect from light and moisture; avoid repeated freeze-thaw. |
| Common analytical method | HPLC-UV or LC-MS | Enzymatic cycling is an alternative for low-abundance samples. |
Measuring NAD+ in biological samples requires rapid processing because the compound can degrade or interconvert after collection. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and mass spectrometry. Each method has different sensitivity, specificity, and susceptibility to interference from related nucleotides. Sample type matters: cultured cells, animal tissues, and human blood present distinct challenges. Reported values can vary widely across laboratories because of differences in extraction, normalization, and analytical platform. Standardization remains an open issue in the field.
NAD+ is relatively unstable in aqueous solution, especially at neutral or alkaline pH and at elevated temperatures. It is typically stored dry, protected from light and moisture, and kept cold or frozen for long-term use. Solutions are often prepared fresh or buffered to mildly acidic pH to slow hydrolysis. Repeated freeze-thaw cycles can reduce integrity. Laboratories may verify concentration using ultraviolet absorbance at 259 nm or by enzymatic assay. These handling practices are general laboratory conventions rather than universal rules.
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.
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.
The nicotinamide ring undergoes reversible reduction at the para position, converting NAD+ to NADH. This reaction transfers a hydride equivalent, not a free hydrogen atom or electron alone. Because the redox pair has a defined reduction potential, it links oxidation of fuels to respiratory chain activity. Many dehydrogenases use NAD+ as a co-substrate and produce NADH. The ratio of NAD+ to NADH reflects metabolic state and influences flux through several pathways.
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.
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.
Quantification of NAD+ in biological samples typically uses liquid chromatography coupled to mass spectrometry. Enzymatic cycling assays offer higher throughput and rely on NAD+ dependent dehydrogenases to amplify signal. Both approaches require careful sample quenching because NAD+ can be rapidly consumed or converted after collection. Acidic extraction is common for NAD+, while alkaline conditions favor NADH in some protocols. Isotopically labeled internal standards help correct for losses during extraction and ionization.
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.
Integrin alpha-11 is a protein that, in humans, is encoded by the ITGA11 gene. This gene encodes an alpha integrin. Integrins are heterodimeric integral membrane proteins composed of an alpha chain and a beta chain. This protein contains an I domain, is expressed in muscle tissue, dimerizes with beta 1 integrin in vitro, and appears to bind collagen in this form. Therefore, the protein may be involved in attaching muscle tissue to the extracellular matrix. Alternative transcriptional splice variants have been found for this gene, but their biological validity is not determined. According to one study, ITGA11 expression is increased in the anterior stroma of corneal buttons excised from the eyes affected by keratoconus. Another study showed that ITGA11 is overexpressed in myofibroblasts in different human fibrotic diseases, including liver cirrhosis, renal fibrosis, and lung fibrosis tissues. ITGA11 has also been found to be upregulated in the tumor stroma of pancreatic ductal adenocarcinoma. Knocking down of ITGA11 in human pancreatic stellate cells led to the inhibition of their differentiation into myofibroblasts and paracrine effect on tumor cells.
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Respiratory acidosis (end-tidal CO2 above 55 mmHg/7.32 kPa or arterial pCO2 above 60 mmHg/7.98 kPa) Heart involvement (unexplained sinus tachycardia, ventricular tachycardia or ventricular fibrillation) Metabolic acidosis (base excess lower than -8, pH <7.25) Muscle rigidity (generalized rigidity including severe masseter muscle rigidity) Muscle breakdown (CK >20,000/L units, cola colored urine or excess myoglobin in urine or serum, potassium above 6 mmol/L) Temperature increase (rapidly increasing temperature, T >38.8 °C) Other (rapid reversal of MH signs with dantrolene, elevated resting serum CK levels) Family history (autosomal dominant pattern)
Sources: en.wikipedia.org
== Distinguishing isozymes == Isozymes (and allozymes) are variants of the same enzyme. Unless they are identical in their biochemical properties, for example their substrates and enzyme kinetics, they may be distinguished by a biochemical assay. However, such differences are usually subtle, particularly between allozymes which are often neutral variants. This subtlety is to be expected, because two enzymes that differ significantly in their function are unlikely to have been identified as isozymes. While isozymes may be almost identical in function, they may differ in other ways. In particular, amino acid substitutions that change the electric charge of the enzyme are simple to identify by gel electrophoresis, and this forms the basis for the use of isozymes as molecular markers. To identify isozymes, a crude protein extract is made by grinding animal or plant tissue with an extraction buffer, and the components of extract are separated according to their charge by gel electrophoresis. Historically, this has usually been done using gels made from potato starch, but acrylamide gels provide better resolution. All the proteins from the tissue are present in the gel, so that individual enzymes must be identified using an assay that links their function to a staining reaction. For example, detection can be based on the localised precipitation of soluble indicator dyes such as tetrazolium salts which become insoluble when they are reduced by cofactors such as NAD or NADP, which generated in zones of enzyme activity.
=== Etymology === Pennsylvania Dutch immigrants to the United States brought the tradition of fresh cheesemaking with them and, by 1831 in Philadelphia, the term cottage cheese was used in the American vocabulary by reference to making cheese in a homestead or "cottage". In 1841, a “cottage industry cheese factory” using milk from homestead cows was established in Wisconsin by Anne Pickett. Cottage cheese referred to homemade soft, white curds served with bread and crackers as Schmierkäse (German term for "smear-cheese" or spreading cheese),
== Cause == G6PD deficiency results from mutations in the G6PD gene. The G6PD gene contributes to the production of glucose-6-phosphate dehydrogenase. Chemical reactions involving glucose-6-phosphate dehydrogenase produce compounds that prevent reactive oxygen species from building up to toxic levels within red blood cells. If a reduction in the amount of glucose-6-phosphate dehydrogenase or alteration of structure occurs due to G6PD gene mutations, the enzyme loses its protective role, leading to the accumulation of reactive oxygen species and thus damaging red blood cells.
Sources: en.wikipedia.org
In contrast to pregabalin, food does not significantly affect the Tmax of gabapentin and increases the Cmax of gabapentin by approximately 10%. The Tmax of the instant-release (IR) formulation of gabapentin enacarbil (as active gabapentin) is about 2.1 to 2.6 hours across all doses (350–2,800 mg) with single administration and 1.6 to 1.9 hours across all doses (350–2,100 mg) with repeated administration. Conversely, the Tmax of the extended-release (XR) formulation of gabapentin enacarbil is about 5.1 hours at a single dose of 1,200 mg in a fasted state and 8.4 hours at a single dose of 1,200 mg in a fed state. The Tmax of phenibut has not been reported, but the onset of action and peak effects have been described as occurring at 2 to 4 hours and 5 to 6 hours, respectively, after oral ingestion in recreational users taking high doses (1–3 g).
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Scott Sinclair served as Bioshock's art director. Once the Rapture setting was chosen, the art team began developing concepts of what the city would look like, inside and out. Art Deco worked well as a style for the environments because its large, simple shapes were easy to replicate with few polygons. The artists drew inspiration from a Gotham-style metropolis, with Hugh Ferriss's architectural illustrations and the Art Deco architecture of New York City providing inspiration for the look and massing of Rapture's skyline. Irrational also wanted to stay away from "tropical" art deco as seen in places like Miami Beach as it did not create the feeling they wanted. Hogarth De La Plante recalled that the team did not want to be too rigid in following a look, instead adapting the style according to their needs. The game's lead level designer was Bill Gardner. He cited Capcom's survival horror series Resident Evil as a significant influence on BioShock, stating there are "all these nods and all these little elements that I think you can see where Resident Evil inspired us". The team were particularly influenced by Resident Evil 4, including its approach to the environments, combat, and tools, its game design and tactical elements, its "gameplay fuelled storytelling" and inventory system, and its opening village level in terms of how it "handled the sandbox nature of the combat" and in terms of "the environment". The focus on a console release helped Irrational refine and simplify the gameplay to make it more accessible.
Sources: en.wikipedia.org
Common methods include enzymatic cycling assays, HPLC with UV detection, and LC-MS. The choice depends on sample size, specificity needs, and available equipment. Rapid quenching before analysis is important because NAD+ and NADH can interconvert.
Water promotes hydrolysis, and heat accelerates degradation. Cold, dry storage slows these processes. Repeated warming and cooling can introduce moisture and condensation, so aliquoting is often used.
Yes. They may be free acid or salts, with different counterions and purity grades. The counterion changes molecular weight, so concentration calculations should account for the actual form. Certificates of analysis provide batch-specific information.
Nicotinamide adenine dinucleotide, with the plus sign indicating the oxidized form. It is a coenzyme present in all living cells. The reduced form is NADH.