This is a working overview of Sirtuins, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-01-28 and is reviewed periodically as new material appears.
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.
Nicotinamide adenine dinucleotide, abbreviated NAD+, is a dinucleotide composed of two nucleotides joined by phosphate groups. One nucleotide contains adenine; the other contains nicotinamide. The molecule exists in oxidized (NAD+) and reduced (NADH) forms, and the reversible hydride transfer between them underlies many metabolic oxidation-reduction reactions. In cells, NAD+ serves as an electron acceptor in pathways such as glycolysis, the citric acid cycle, and oxidative phosphorylation. Its concentration and redox ratio vary by compartment, tissue, and metabolic state.
Beyond redox chemistry, NAD+ is consumed as a substrate by enzymes that transfer ADP-ribose or remove acetyl groups. Sirtuins use NAD+ in deacylation reactions, poly(ADP-ribose) polymerases use it in DNA damage responses, and CD38 hydrolases convert it to signaling metabolites. Because these enzymes compete for the same pool, changes in NAD+ availability can influence multiple cellular processes. The relative contribution of each consumption route differs by cell type and condition, and precise quantitative links remain an active area of study.
Research on NAD+ spans biochemistry, aging biology, and metabolism. Studies often examine how NAD+ levels change with age, diet, exercise, or disease states, and whether precursor supplementation alters those levels. Findings in animal models do not automatically translate to humans, and measurement methods vary across studies. Questions about tissue-specific effects, long-term consequences, and causal relationships remain open. NAD+ itself is not established as a single therapeutic agent with a broad clinical role.
| 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 |
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.
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.
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.
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.
where the carbon-12 nucleus used in the first reaction is regenerated in the last reaction. After the two positrons (emitted by beta-plus decay) annihilate with two ambient electrons producing an additional 2.04 MeV, the total energy released in one cycle is 26.73 MeV; in some texts, authors are erroneously including the positron annihilation energy in with the Q-value for beta-decay and then neglecting the equal amount of energy released by annihilation, leading to possible confusion. All values are calculated with reference to the Atomic Mass Evaluation 2003. The limiting (slowest) reaction in the CNO-I cycle is the proton capture on 147N. In 2006 it was experimentally measured down to stellar energies, revising the calculated age of globular clusters by around 1 billion years. The neutrinos emitted in beta decay will have a spectrum of energy ranges, because although momentum is conserved, the momentum can be shared in any way between the positron and neutrino, with either emitted at rest and the other taking away the full energy, or anything in between, so long as all the energy from the Q-value is used. The total momentum received by the positron and the neutrino is not great enough to cause a significant recoil of the much heavier daughter nucleus and hence, its contribution to kinetic energy of the products, for the precision of values given here, can be neglected. Thus the neutrino emitted during the decay of nitrogen-13 can have an energy from zero up to 1.20 MeV, and the neutrino emitted during the decay of oxygen-15 can have an energy from zero up to 1.73 MeV.
==== Dopamine precursors and related ==== Carbidopa (Lodosyn) – aromatic L-amino acid decarboxylase (AAAD) inhibitor Carbidopa/levodopa (Crexont; IPX-203; IPX203) – combination of carbidopa (aromatic L-amino acid decarboxylase (AAAD) inhibitor) and levodopa (dopamine precursor) [324] Foscarbidopa/foslevodopa (ABBV-951; foslevodopa/foscarbidopa; levodopa/carbidopa prodrug; Produodopa; Vyalev) – combination of foscarbidopa (aromatic L-amino acid decarboxylase (AAAD) inhibitor) and foslevodopa (dopamine precursor) [325] Levodopa (CVT-301; CXG-89; Inbrija) – dopamine precursor and indirect non-selective dopamine receptor agonist [326] Levodopa/benserazide (co-beneldopa) (Madopar, Prolopa) – combination of levodopa (dopamine precursor) and benserazide (aromatic L-amino acid decarboxylase (AAAD) inhibitor) Levodopa/carbidopa extended-release (GSK-587124; IPX-066; Numient; Patrome; Rytary) – combination of levodopa (dopamine precursor) and carbidopa (aromatic L-amino acid decarboxylase (AAAD) inhibitor) [327] Levodopa/carbidopa intraduodenal (ABT-SLV187; carbidopa/levodopa enteral suspension; Duodopa; Duopa; LCIG; levodopa/carbidopa intestinal gel) – combination of levodopa (dopamine precursor) and carbidopa (aromatic L-amino acid decarboxylase (AAAD) inhibitor) [328] Melevodopa/carbidopa (carbidopa/melevodopa; CHF-1512; CNP-1512; GT-1512; levodopa methyl ester/carbidopa; Sirio; V-1512) – combination of melevodopa (dopamine precursor) and carbidopa (aromatic L-amino acid decarboxylase (AAAD) inhibitor) [329]
== Indications == DBNPA is used as a disinfectant, bactericide, algicide, slime remover, and mildew inhibitor in several industrial applications. It is frequently used to regulate the growth of bacteria, algae, and slime in oilfield water injection systems and circulating cooling water systems. DBNPA is used in the paper industry as a slime remover, bactericide, and algicide to keep machinery free of microorganisms and maintain product quality. Additionally, it is utilized as a preservative to prevent microbiological deterioration in paints, waxes, inks, detergents, surfactants, slurries, and resins. DBNPA also serves as a fungicide and algaecide in municipal water landscapes, guaranteeing water safety and clarity, and as a biocide in process water and air purifier systems in the machinery manufacturing sector. The concentration used when it is being used as a water treatment slime stripper is 30~50 mg/L. When it is being used for water treatment, as a bactericide, it is used at a concentration of 10~20 mg/L. In terms of analytical detection in industrial and environmental samples, high-performance liquid chromatography with UV detection, measuring absorption at 230 nm, detects DBNPA at extremely low concentrations (>0.1 mg/L) in water samples. Gas chromatography-mass spectrometry can also identify and quantify DBNPA and the associated degradation products, (detection limit is 0.05 mg/L) in environmental samples.
Sources: en.wikipedia.org
=== Common names === There are many common names for S. divinorum, including sage of the diviners, ska maría pastora, seer's sage, yerba de la pastora, simply salvia, and colloquially sally-d and magic mint.
==== Electrospinning ==== Electrospinning is a highly versatile technique that can be used to produce continuous fibers ranging in diameter from a few microns to a few nanometers. In a typical electrospinning set-up, the desired scaffold material is dissolved within a solvent and placed within a syringe. This solution is fed through a needle and a high voltage is applied to the tip and to a conductive collection surface. The buildup of electrostatic forces within the solution causes it to eject a thin fibrous stream towards the oppositely charged or grounded collection surface. During this process the solvent evaporates, leaving solid fibers leaving a highly porous network. This technique is highly tunable, with variation to solvent, voltage, working distance (distance from the needle to collection surface), flow rate of solution, solute concentration, and collection surface. This allows for precise control of fiber morphology. On a commercial level however, due to scalability reasons, there are 40 or sometimes 96 needles involved operating at once. The bottle-necks in such set-ups are: 1) Maintaining the aforementioned variables uniformly for all of the needles and 2) formation of "beads" in single fibers that we as engineers, want to be of a uniform diameter. By modifying variables such as the distance to collector, magnitude of applied voltage, or solution flow rate – researchers can dramatically change the overall scaffold architecture.
=== Laws === There are no laws as such in the Culture. Social norms are enforced by convention (personal reputation, "good manners", and by, as described in The Player of Games, possible ostracism and involuntary supervision for more serious crimes). Minds generally refrain from using their all-seeing capabilities to influence people's reputations, though they are not necessarily themselves above judging people based on such observations, as described in Excession. Minds also judge each other, with one of the more relevant criteria being the quality of their treatment of sentients in their care. Hub Minds for example are generally nominated from well-regarded GSV (the largest class of ships) Minds, and then upgraded to care for the billions living on the artificial habitats. Serious prohibitions exist against harming sentient beings, or forcing them into undertaking any act (another concept that seems unnatural to and is, in fact, almost unheard of by almost all Culture citizens). As mentioned in The Player of Games, the Culture does have the occasional "crime of passion" (as described by an Azadian) and the punishment was to be "slap-droned", or to have a drone assigned to follow the offender and "make sure [they] don't do it again". While the enforcement in theory could lead to a Big Brother-style surveillance society, in practice social convention among the Minds prohibits them from watching, or interfering in, citizens' lives unless requested, or unless they perceive severe risk.
== Cause == A primary cause of wound dehiscence is sub-acute infection, resulting from inadequate or imperfect aseptic technique. Coated suture, such as Vicryl, generally breaks down at a rate predicted to correspond with tissue healing, but is hastened in the presence of bacteria. In the absence of other known metabolic factors which inhibit healing and may have contributed to suture dehiscence, subacute infection should be suspected, and the protocol for obtaining wound cultures followed. Dehiscence can also be caused by inadequate undermining (cutting the skin away from the underlying tissues) of the wound during surgery, excessive tension on the wound edges caused by the act of lifting or straining, or the wound being located on a highly mobile or high-tension area such as the back, shoulders or legs. Individuals with Ehlers–Danlos syndrome also commonly experience wound dehiscence. Risk factors for dehiscence can include any of the above, as well as obesity, smoking, previous scarring, surgical error, cancer, chronic use of corticosteroids and increased abdominal pressure. A very common cause is also use of nicotine in any form.
Sources: en.wikipedia.org
A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today's food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently. Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic metres (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.
== Absorption and metabolism == NMNH has proven to be a more effective NAD+ enhancer than NMN, achieving a 5-fold increase in NAD+ levels and sustaining elevated levels for six hours while maintaining high levels for up to 24 hours. NMNH treatment leads to a similar trend in NAD+ and NADH biosynthesis as NMN treatment, implying a shared pathway. However, NMNH was shown to inhibit the endogenous synthesis of NMN by blocking the action of nicotinamide phosphoribosyl transferase (NAMPT) This inhibition suggests that NMNH may be more effective than NMN in directly stimulating NAD+ production.
turgor pressure Also turgidity. The force within a cell which pushes the plasma membrane against the cell wall, a type of hydrostatic pressure influenced by the osmotic flow of water into and out of the cell. Turgidity is observed in plants, fungi, bacteria, and some protists with cell walls, but generally not in animal cells.
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+ is a coenzyme found in all living cells. It carries electrons in metabolic reactions and also serves as a substrate for enzymes involved in signaling and DNA repair. Its oxidized and reduced forms are central to energy metabolism.