freeze-thaw raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-10-03 and is reviewed periodically as new material appears.
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.
Beyond redox catalysis, NAD+ is a substrate for enzymes that transfer ADP-ribose or remove acetyl groups from proteins. Sirtuins and poly(ADP-ribose) polymerases consume NAD+ and release nicotinamide as a byproduct. These reactions connect cellular energy status to gene regulation, DNA repair, and stress responses. Because NAD+ is used rather than merely recycled in such signaling, its concentration reflects both biosynthesis and consumption. The balance between salvage and de novo synthesis pathways determines available pools in different tissues.
Biosynthesis of NAD+ starts from nicotinamide, nicotinic acid, or nicotinamide riboside through salvage pathways. A rate-limiting enzyme, nicotinamide phosphoribosyltransferase, converts nicotinamide to nicotinamide mononucleotide. Further coupling with ATP yields NAD+. In mammals, the liver and muscle can synthesize NAD+ from dietary precursors, but tissue levels vary widely. Researchers study these pathways to understand age-related changes, metabolic disorders, and neurodegeneration. Direct causal links between NAD+ decline and disease remain an active area of investigation.
| Property | Value | Notes |
|---|---|---|
| Molar mass | 663.43 g/mol | For the free acid form; salts have higher mass. |
| Appearance | White to off-white powder | Often hygroscopic; may clump on exposure to air. |
| Solubility | Freely soluble in water | Poorly soluble in nonpolar organic solvents. |
| Typical storage | -20 °C, desiccated | Protect from light and moisture; avoid repeated freeze-thaw. |
| Common synonyms | beta-NAD, DPN | DPN stands for diphosphopyridine nucleotide, an older name. |
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.
Quantification of NAD+ in biological samples usually relies on separation techniques coupled to sensitive detection. High-performance liquid chromatography with ultraviolet detection can measure the oxidized form by its absorbance near 260 nm, while mass spectrometry provides greater specificity and can distinguish NAD+ from close analogs. Enzymatic cycling assays use coupled dehydrogenase reactions to amplify signal and estimate NAD+ concentrations in cell or tissue extracts. Because NAD+ and NADH interconvert rapidly, sample preparation must quench metabolism quickly and preserve the redox state before analysis.
The stability of NAD+ depends on pH, temperature, light exposure, and the presence of degradative enzymes. Aqueous solutions are generally more stable under mildly acidic to neutral conditions and degrade faster under alkaline conditions or prolonged heat. The solid is hygroscopic and should be stored desiccated, often frozen, and protected from repeated freeze-thaw cycles. In laboratory handling, aliquots reduce repeated temperature changes, and chelating agents may limit metal-catalyzed hydrolysis in some buffers. These practices matter because even small amounts of NADH or hydrolysis products can interfere with quantitative assays.
Quality control for NAD+ materials typically combines identity, purity, and water content checks. Identity may be confirmed by ultraviolet spectrum, retention time in chromatography, or mass accuracy, while purity is assessed by HPLC peak area or quantitative nuclear magnetic resonance. Residual water and solvents can affect molar calculations and enzyme assays, so Karl Fischer titration or thermogravimetric analysis may be used. Commercial materials vary in grade and counterion form, and published methods should specify the exact salt or hydrate when reporting concentrations. Regulatory status depends on intended use, with research reagents, dietary ingredients, and clinical products treated under different frameworks.
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.
Quality control for NAD+ relies on identity, purity, and functional tests. A certificate of analysis may report high-performance liquid chromatography purity, ultraviolet spectrum, water content, and residual solvents. Because NAD+ is hygroscopic, gravimetric values can shift as material absorbs water, so purity should be interpreted alongside storage history. Mass spectrometry confirms molecular identity, while enzymatic assays show whether the material supports dehydrogenase activity. Commercial material is available as the free acid and as salts, and the counterion affects molecular weight, solubility, and how concentrations are calculated.
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.
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.
Occasionally, a group of spiders may build webs together in the same area. Massive flooding in Pakistan during the 2010 monsoon drove spiders above the waterline, into trees. The result was trees covered with spider webs. One such web, reported in 2007 at Lake Tawakoni State Park in Texas, measured 200 yards (180 m) across. Entomologists believe it may be the result of social cobweb spiders or of spiders building webs to spread out from one another. There is no consensus on how common this occurrence is. In Brazil, there have been two instances of a phenomenon that became known as "raining spiders"; communal webs made by "social" spiders that cover such wide gaps and which strings are so difficult to see that hundreds of spiders seem to be floating in the air. The first occurred in Santo Antônio da Platina, Paraná, in 2013, and involved Anelosimus eximius individuals; the second was registered in Espírito Santo do Dourado, Minas Gerais, in January 2019, and involved Parawixia bistriata individuals. A web over 100 square metres (1,100 sq ft) built by thousands of Tegenaria domestica (which was not previously known to form colonies) and shared by Prinerigone vagans was found in the Sulfur Cave between Greece and Albania. The discoverers hypothesize that the darkness and size difference allow P. vagans not to be predated by the larger T. domestica. The colony is sustained by an abundance of chemoautotrophic bacteria and its predators.
== Overview == The pub was the home to the Cantabrigensis Hash House Harriers between 1993 and 2017, a rowing club and a cricket team. It was the start/finish venue on the legendary King Street Run. All of these activities and more were encouraged (and in the case of the cricket team, started) by Terry Kavanagh (1937-2012), who was landlord between 1992 and 2009. Since 1992 the St Radegund has played an annual cricket match against The Champion of the Thames, for the King Street Trophy. In 2008, the saga of the 2003 St Radegund cricket tour to Croatia, The Ascent of Mount Hum, was published, to critical acclaim. Friday night is Vera Lynn Appreciation Society night when large amounts of gin and tonics were served along with to Vera Lynn’s songs. In 2007, it was pointed out that the pub sign depicted the arms of the Austrian municipality, Sankt Radegund bei Graz rather than the saint herself. A local artist was commissioned to correct the mistake and the story attracted media comment. In 2010, the new landlord, James Hoskins, reverted to a design incorporating the former (incorrect) arms. In early 2015 the premises underwent a programme of refurbishment and redecoration after which it became a pub tied to the Saffron Brewery, ceasing to serve Habit and Sackcloth, beers specially brewed for the pub by Milton Brewery. It was closed under notice of forfeiture in August 2019. In 2020 Cold Chain Bars obtained the lease and the pub reopened in March 2024 before closing again in October of the same year.
=== United Kingdom === The legal status of powdered alcohol in United Kingdom is uncertain, although parliament saw no dangers from the sale of powdered alcohol, aside from the loss of tax revenue. In a January 2015 answer to a parliamentary question, Lord Bates wrote "The Government is aware of powdered alcohol from media reports and the banning of the product in five states of the United States of America. The Government is aware of powdered alcohol being marketed and made available in the coming years to buy in England and Wales."
==== 2026 ==== Scientists at the University of New Mexico reported that the enzyme OTULIN, known for regulating immune activity, plays a major role in producing Tau proteins, which are associated with neurodegenerative disorders including Alzheimer's disease, brain inflammation, and aging. The research team found that disabling OTULIN stopped Tau production and removed existing Tau from neurons. A study at the Weizmann Institute of Science suggested that genetics play a larger role in determining human lifespan than previously believed, estimating that longevity is 50% heritable, about double what previous studies had concluded and matching the findings of lifespan studies in animals. A research team led by Johannes Gräff at EPFL found that partial reprogramming of engram neurons reversed cognitive decline in aged mice as well as mice with Alzheimer's. Scientists at the University of Rochester successfully transferred a longevity-related gene from naked mole rats to mice, which made the mice healthier and extended their lifespans. A study at the University of Sydney reported that a four-week diet change in older adults, with reduced fat intake or shift to plant-based protein, improved key health biomarkers tied to aging, with a low-fat and high-carb diet giving the strongest results. A study at the University of Texas Medical Branch found that transplanting a youthful gut microbiome into aging mice reversed aging in the liver and prevented liver cancer.
Sources: en.wikipedia.org
An L-ribonucleic acid aptamer (L-RNA aptamer, trade name Spiegelmer) is an RNA-like molecule built from L-ribose units. It is an artificial oligonucleotide named for being a mirror image of natural oligonucleotides. L-RNA aptamers are a form of aptamers. Due to their L-nucleotides, they are highly resistant to degradation by nucleases. L-RNA aptamers are considered potential drugs and are currently being tested in clinical trials.
== Development == The basis of GoldSrc is the engine used in the video game Quake, albeit with heavy modification by Valve. While the engine served as the basis for GoldSrc, Gabe Newell said that a majority of the code used in the engine was created by Valve. GoldSrc's artificial intelligence systems, for example, were essentially made from scratch. The engine also uses some code from other games in the Quake series, including QuakeWorld and Quake II. In 1997, Valve hired Ben Morris and acquired Worldcraft, a tool for creating custom Quake maps. The tool was renamed Valve Hammer Editor and became the official mapping tool for GoldSrc. The engine supports skeletal animation, which allowed for more realistic body kinematics and facial expression animations than most other engines at the time of release. The GoldSrc engine initially had no real name and was simply called the Half-Life engine. When the need arose for Valve to work on the engine without risking introducing bugs into Half-Life's codebase, Valve forked the code, creating two main engine branches: one gold master branch, "GoldSrc", and the other "Src". Internally, any games using the original branch were referred to as "Goldsource" to differentiate it from the second branch, while the "Src" branch evolved into the Source engine. Valve released versions of the GoldSrc engine for OS X and Linux in 2013, eventually porting all of their first-party games using the engine to the platforms by the end of the year.
Jasmonates (JAs) are lipid-based hormones that were originally isolated from jasmine oil. JAs are especially important in the plant response to attack from herbivores and necrotrophic pathogens. The most active JA in plants is jasmonic acid. Jasmonic acid can be further metabolized into methyl jasmonate (MeJA), which is a volatile organic compound. This unusual property means that MeJA can act as an airborne signal to communicate herbivore attack to other distant leaves within one plant and even as a signal to neighboring plants. In addition to their role in defense, JAs are also believed to play roles in seed germination, the storage of protein in seeds, and root growth. JAs have been shown to interact in the signalling pathway of other hormones in a mechanism described as "crosstalk." The hormone classes can have both negative and positive effects on each other's signal processes. Jasmonic acid methyl ester (JAME) has been shown to regulate genetic expression in plants. They act in signalling pathways in response to herbivory, and upregulate expression of defense genes. Jasmonyl-isoleucine (JA-Ile) accumulates in response to herbivory, which causes an upregulation in defense gene expression by freeing up transcription factors. Jasmonate mutants are more readily consumed by herbivores than wild type plants, indicating that JAs play an important role in the execution of plant defense.
Sources: en.wikipedia.org
== Overview == The process of translation starts with the information stored in the nucleotide sequence of DNA. This is first transformed into mRNA, then tRNA specifies which three-nucleotide codon from the genetic code corresponds to which amino acid. Each mRNA codon is recognized by a particular type of tRNA, which docks to it along a three-nucleotide anticodon, and together they form three complementary base pairs. On the other end of the tRNA is a covalent attachment to the amino acid corresponding to the anticodon sequence, with each type of tRNA attaching to a specific amino acid. Because the genetic code contains multiple codons that specify the same amino acid, there are several tRNA molecules bearing different anticodons which carry the same amino acid. The covalent attachment to the tRNA 3' end is catalysed by enzymes called aminoacyl tRNA synthetases. During protein synthesis, tRNAs with attached amino acids are delivered to the ribosome by proteins called elongation factors, which aid in association of the tRNA with the ribosome, synthesis of the new polypeptide, and translocation (movement) of the ribosome along the mRNA. If the tRNA's anticodon matches the mRNA, another tRNA already bound to the ribosome transfers the growing polypeptide chain from its 3' end to the amino acid attached to the 3' end of the newly delivered tRNA, a reaction catalyzed by the ribosome. A large number of the individual nucleotides in a tRNA molecule may be chemically modified, often by methylation or deamidation.
== Clinical relevance == Pyruvate dehydrogenase deficiency (PDCD) can result from mutations in any of the enzymes or cofactors used to build the complex. Its primary clinical finding is lactic acidosis. Such PDCD mutations, leading to subsequent deficiencies in NAD and FAD production, hinder oxidative phosphorylation processes that are key in aerobic respiration. Thus, acetyl-CoA is instead reduced via anaerobic mechanisms into other molecules like lactate, leading to an excess of bodily lactate and associated neurological pathologies. While pyruvate dehydrogenase deficiency is rare, there are a variety of different genes when mutated or nonfunctional that can induce this deficiency. First, the E1 subunit of pyruvate dehydrogenase contains four different subunits: two alpha subunits designated as E1-alpha and two beta subunits designated as E1-beta. The PDHA1 gene found in the E1-alpha subunits, when mutated, causes 80% of the cases of pyruvate dehydrogenase deficiency because this mutation abridges the E1-alpha protein. Decreased functional E1 alpha prevents pyruvate dehydrogenase from sufficiently binding to pyruvate, thus reducing the activity of the overall complex. When the PDHB gene found in the E1 beta subunit of the complex is mutated, this also leads to pyruvate dehydrogenase deficiency.
== Genetics == The biologic instructions for synthesising protein C in humans are encoded in the gene officially named "protein C (inactivator of coagulation factors Va and VIIIa)". The gene's symbol approved by the HUGO Gene Nomenclature Committee is "PROC" from "protein C". It is located on the second chromosome (2q13-q14) and comprises nine exons. The nucleotide sequence that codes for human protein C is approximately 11,000 bases long.
Sources: en.wikipedia.org
It indicates the oxidized form, which has a positive charge on the nicotinamide nitrogen. The reduced partner NADH lacks that charge and carries added electrons. The plus sign is part of the standard abbreviation, not a separate ion.
No. It also serves as a substrate for signaling and DNA-repair enzymes such as sirtuins and PARPs. Those reactions consume NAD+ and connect its availability to cellular regulation. Energy transfer remains its most abundant known role.
NAD+ is the oxidized electron acceptor, while NADH is the reduced electron carrier. They form a reversible redox pair and differ by a hydride ion. Cells maintain different ratios of the two depending on conditions and compartment.
NAD+ is the oxidized form and NADH is the reduced form of the same coenzyme. NAD+ accepts electrons during oxidation reactions, becoming NADH, which can donate electrons in other reactions. The ratio between them helps describe a cell's redox state.