If you have been reading about Sirtuins and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-09-24. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
In aqueous solution, NAD+ is most stable under mildly acidic to neutral conditions and degrades faster at high pH or elevated temperature. The molecule can hydrolyze at the pyrophosphate bond or undergo nonenzymatic cyclization. Buffers, chelating agents, and cold temperatures slow these losses during analysis. Repeated freeze-thaw cycles are generally avoided because they can promote degradation and concentration changes. Light exposure is also controlled, though NAD+ is less photolabile than some related nucleotides.
Commercial NAD+ is supplied as a solid, often as the free acid or a salt, and purity is verified by chromatographic methods. Laboratories typically store it desiccated at minus 20 degrees Celsius or below. Working solutions are prepared fresh because even sterile aqueous solutions can lose activity over hours to days depending on pH and temperature. Documentation may include a certificate of analysis, an assay value, and a recommended retest date. Researchers should verify identity and purity when results depend on precise cofactor concentrations.
NAD+ is commonly measured by high-performance liquid chromatography with ultraviolet detection, often at 254 or 260 nm. Enzymatic cycling assays provide higher sensitivity by coupling NAD+ to a reporter reaction. Mass spectrometry can distinguish NAD+ from close analogues and confirm isotope labeling. Sample preparation usually involves rapid quenching of metabolism to prevent interconversion with NADH. Because NAD+ and NADH differ by one hydride, extraction conditions strongly affect the measured ratio.
| Property | Value | Notes |
|---|---|---|
| IUPAC name | Nicotinamide adenine dinucleotide | Oxidized dinucleotide form |
| CAS Registry Number | 53-84-9 | Common entry for beta-NAD+ |
| Molecular formula | C21H27N7O14P2 | Free acid form |
| Molar mass | 663.43 g/mol | Calculated for free acid |
| Water solubility | Freely soluble | Charged dinucleotide; less soluble in organic solvents |
Nicotinamide adenine dinucleotide, commonly abbreviated NAD+, is a coenzyme present in all living cells. The molecule consists of two nucleotides linked by phosphate groups, with adenine and a nicotinamide ring as its principal features. In its oxidized form, the nicotinamide ring can accept a hydride ion, becoming NADH. This reversible conversion places NAD+ at the center of many electron-transfer reactions. Its role as a redox carrier is well established across bacteria, plants, fungi, and animals.
Beyond redox chemistry, NAD+ acts as a substrate for several enzyme families. ADP-ribosyltransferases, sirtuins, and CD38 ectoenzymes cleave the molecule into nicotinamide and ADP-ribose or related products. These reactions connect NAD+ availability to processes such as DNA repair, chromatin modification, and calcium signaling. Because the coenzyme is used in both electron transfer and signaling, cells maintain separate pools in compartments including the cytosol, mitochondria, and nucleus. The relative sizes and regulation of those pools remain active areas of study.
Cells produce NAD+ through several biosynthetic routes. The salvage pathway recycles nicotinamide, while the Preiss-Handler pathway uses nicotinic acid, and a de novo route can start from tryptophan in some organisms. In mammals, the salvage pathway is generally considered the main source under ordinary conditions. Tissue concentrations vary widely by cell type and compartment, and measured declines with age have been reported in some studies. Whether such changes drive aging or mainly accompany it remains an open question.
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.
"Service With the Speed of Sound" (1958) "Happy Eating" (1980s: on signs at many of the company's drive-ins) "America's Drive-In" (1987) "Faster and Better than Ever" (1988–1990) "No Place Hops like Sonic" (1990–1993) "Summer's Funner" (1993) "Drive-In for a Change" (1995–1997) "All Summer Long" (1997) "It's Sonic Good" (2003-2011) "Sonic's Got It, Others Don't" (2007) "Even Sweeter After Dark" (2009) "This is How You Sonic" (2011–2020) "Sonic Everywhere" (2016) "You Guys Wanna Hang Out Sometime" (2016) “This Is How We Sonic” (2020) "Mmm. Sonic." (2022) “Live Free, Eat Sonic” (2024)
=== Pseudobulbar affect === In 2010, the FDA approved the combination drug dextromethorphan/quinidine under the brand name Nuedexta for the treatment of pseudobulbar affect (uncontrollable laughing/crying). Dextromethorphan is the active therapeutic agent in the combination; quinidine merely serves to inhibit the enzymatic degradation of dextromethorphan and thereby increase its circulating concentrations via inhibition of CYP2D6.
"...and much more likely to endure their miseries publicly; a tired walker, after all, merely sits down – a tired cyclist falls off and possibly brings others crashing down as well. That's much more fun". The fascination with six-day bicycle races spread across the Atlantic and appealed to the crowds in America as well. And the more spectators paid at the gate, the higher the prizes could be and the greater was the incentive of riders to stay awake—or be kept awake—to ride the greatest distance. Their exhaustion was countered by soigneurs (the French word for "healers"), helpers akin to seconds in boxing. Among the treatments they supplied was nitroglycerine, a drug used to stimulate the heart after cardiac attacks and which was credited with improving riders' breathing. Riders had hallucinations from the exhaustion and perhaps the drugs. The American champion Major Taylor refused to continue the New York race, saying: "I cannot go on with safety, for there is a man chasing me around the ring with a knife in his hand." Public reaction turned against such trials, whether individual races or in teams of two. One report said:
The SADC has specifically emphasised the importance of combating non-traditional maritime threats as part of the 2050 Integrated Maritime Strategy. The Bay of Bengal Initiative for Multi-Sectoral Technical and Economic Cooperation (BIMSTEC), has enabled the states within the Bay of Bengal to create greater maritime security through collaboration between countries. Furthermore, BIMSTEC has launched a Convention on Cooperation in Combating International Terrorism, Organised Crime and Illicit Drug Trafficking. This facilitates regional cooperation specific to the illicit drug trade, and provides the region with the foundations to develop their response further. The existing regional and individual responses by states have, in practice, been limited to seizure-based responses. This is due to gaps in the current legal infrastructure, which prevent effective prosecution of smugglers following drug seizures. Huge drug seizures have been made by both the Combined Maritime Forces (CMF) and the Combined task force (CTF), such as when the CTF successfully seized 6.2 tonnes of hashish over two days. However, gaps in the current laws prevent further action. One such example is Article 110 of the UNSC Law of the Sea Convention 1982, which does not include a suspicion of drug smuggling as a legitimate reason to board a vessel without gaining permission from the ship’s flagged country. This has decreased the amount of possible seizures, and gaining permission to board vessels is complicated by insufficient regional cooperation within the criminal justice system.
Sources: en.wikipedia.org
Overlapping peptide libraries - in which the entirety of a larger protein is used to produce a library of 8-20 amino acid peptides which overlap; these libraries can be used to identify the specific regions of a larger protein which participate in a given interaction or to provide pre-digested versions of a larger protein for binding. Truncation peptide libraries - in which a given peptide is produced with various or all N or C terminal truncations, these smaller fragments can be used to identify the minimal required region of a peptide for a given interaction being studied. Random libraries - randomly generated peptides of a set length, or range of lengths, can be used to identify novel binding partners of a target of interest. Alanine scanning libraries - in which each amino acid of a given protein or peptide is replaced with an alanine sequentially such that each peptide contains only one alanine mutations but all possible mutations to alanine are present; this can be used to identify critical residues for binding Positional or scrambled peptide libraries - in which specific positions in the peptide are substituted for many or all other amino acids such that the effect of each amino acid at that position in the peptide on the binding or other activity of the peptide can be tested. Scrambled libraries are often random peptides and used as negative controls. Solid phase peptide synthesis is limited to a peptide chain length of approximately 70 amino acids and is generally unsuitable for the study of larger proteins.
Alcohol has a variety of short-term and long-term adverse effects. Alcohol has both short-term, and long-term effects on the memory, and sleep. It also has reinforcement-related adverse effects, including alcoholism, dependence, and withdrawal. Alcohol use is directly related to considerable morbidity and mortality, for instance due to intoxication and alcohol-related health problems. The World Health Organization advises that there is no safe level of alcohol consumption. Many of the toxic and unpleasant actions of alcohol in the body are mediated by its carcinogenic byproduct acetaldehyde.
== History == Originally discovered and developed by Eli Lilly, oritavancin was acquired by Intermune in 2001, and then by Targanta Therapeutics in 2005. In 2009, The Medicines Company acquired the development rights, completed clinical trials and submitted a new drug application to the FDA in February 2014. In August 2014, the US Food and Drug Administration approved oritavancin to treat skin infections. A marketing authorization valid throughout the European Union was granted in March 2015, for the treatment of acute bacterial skin and skin structure infections in adults.
Sources: en.wikipedia.org
=== Longevity === Giant tortoises are among the longest-lived vertebrate animals (over 100 years by some estimates) and have been used as a model for studying longevity. DNA analysis of the genomes of Lonesome George, the iconic last member of Chelonoidis abingdonii, and the Aldabra giant tortoise Aldabrachelys gigantea led to the detection of lineage-specific variants affecting DNA repair genes that might contribute to our understanding of increased lifespan.
These analogues were studied for neurodegenerative diseases, demonstrating improved stability and brain penetration, strong binding affinity to the targeted receptors, and positive effects on cognitive function and neuroprotection in animal models. IRAP inhibitors have also been found to counteract acetylcholine-induced vasoconstriction in vivo, highlighting IRAP's role in modulating vascular function. IRAP deletion reduces susceptibility to pentylenetetrazol-induced seizures in mice, suggesting its potential as epilepsy therapeutic target. IRAP plays an important role in the regulation of the immune system. Similarly to ERAP1 and ERAP2, IRAP is able to trim the N-terminal of antigenic peptides, reducing their length to 8-10 amino acids, the optimal length for MHC class I binding. In contrast to ERAP1 and ERAP2, there is no evidence of IRAP-mediated trimming of antigenic peptides in the endoplasmic reticulum for the MHC-I presentation through the direct pathway. On the other hand, IRAP has a primary function in cross-presentation. Here, the aminopeptidase trims cross-presented peptides in a specific endosomal compartment, described in dendritic cells, before their loading on IRAP-associated MHC class I molecules. IRAP stabilizes the particular type of regulated early endosomes it is located in. The stability of these endosomes is essential for the cross-presentation pathway in dendritic cells, and regulates several endosomal signaling pathways (TCR, TLR9, TNFα, IL-6) in other immune cell types.
=== Reducing agent compatible (RAC) BSA assay === This type of BCA assay includes a proprietary thiol covalent blocking "Compatibility Reagent" a.k.a. a Reducing Agent Compatibility Agent (RACA). Although this allows greater compatibility with reducing agents, the assay has a different interference profile from other non-protein components.
The Bolshevik government then established the Cheka (All-Russian Extraordinary Commission) secret police to eliminate anti–Bolshevik opposition in the country. Initially, there was strong opposition to the Bolshevik régime because they had not resolved the food shortages and material poverty of the Russian peoples as promised in October 1917. From that social discontent, the Cheka reported 118 uprisings, including the Kronstadt rebellion (7–17 March 1921) against the economic austerity of the War Communism imposed by the Bolsheviks. The principal obstacles to Russian economic development and modernisation were great material poverty and the lack of modern technology which were conditions that orthodox Marxism considered unfavourable to communist revolution. Agricultural Russia was sufficiently developed for establishing capitalism, but it was insufficiently developed for establishing socialism. For Bolshevik Russia, the 1921–1924 period featured the simultaneous occurrence of economic recovery, famine (1921–1922) and a financial crisis (1924). By 1924, considerable economic progress had been achieved and by 1926 the Bolshevik government had achieved economic production levels equal to Russia's production levels in 1913. Initial Bolshevik economic policies from 1917 to 1918 were cautious, with limited nationalisations of the means of production which had been private property of the Russian aristocracy during the Tsarist monarchy.
Sources: en.wikipedia.org
NAD+ is the oxidized form, while NADH is the reduced form carrying an added hydride. The two form a redox pair that cells use in many energy-yielding reactions.
NAD+ is a small organic cofactor, not a protein or enzyme. It binds temporarily to enzymes such as dehydrogenases to assist electron transfer.
Intact NAD+ is generally not taken up efficiently by most cells because it is charged and water-soluble. Cells often rely on precursors such as nicotinamide or nicotinamide riboside to produce NAD+ internally.
NAD+ and NADH can interconvert quickly after a sample is collected, which can alter the measured ratio. Rapid quenching and cold handling limit enzymatic and chemical changes.