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 2026-03-13 and is reviewed periodically as new material appears.
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.
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.
Beyond redox chemistry, NAD+ serves as a substrate for enzymes that cleave the molecule and transfer its ADP-ribose moiety or remove acetyl groups. Sirtuins consume NAD+ during deacetylation, poly(ADP-ribose) polymerases use it in DNA damage responses, and CD38 enzymes hydrolyze it to signaling metabolites. These consumption pathways mean that NAD+ availability can influence gene regulation, DNA repair, and calcium signaling. Cellular NAD+ concentrations decline in some tissues with age in animal models, but whether this decline is a cause or consequence of aging in humans remains an active open question.
Nicotinamide adenine dinucleotide, commonly abbreviated NAD+, is a dinucleotide coenzyme built from an adenine nucleotide and a nicotinamide nucleotide joined by a pyrophosphate linkage. Its oxidized form carries a positive charge on the nicotinamide ring, while the reduced form, NADH, carries a hydride equivalent. The molecule participates in hundreds of oxidoreductase reactions, where it accepts or donates electrons and protons. Because it can cycle between oxidized and reduced states without net consumption, NAD+ functions as a reusable electron carrier rather than a fuel molecule.
| 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 |
In glycolysis, NAD+ accepts electrons during the oxidation of glyceraldehyde-3-phosphate, forming NADH. The tricarboxylic acid cycle and fatty acid oxidation also generate NADH, which donates electrons to the mitochondrial electron transport chain. This flow supports ATP synthesis and helps maintain the redox balance of the cell. Other dehydrogenases use NAD+ as a cofactor for biosynthetic reductions and detoxification reactions. NADH is later reoxidized to sustain continued flux through these pathways.
Beyond electron transfer, NAD+ serves as a substrate for enzymes that cleave the molecule and transfer ADP-ribose units. Sirtuins, poly(ADP-ribose) polymerases, and CD38 consume NAD+ in regulatory reactions. These activities link NAD+ availability to DNA repair, chromatin modification, calcium signaling, and metabolic stress responses. Because consumption can exceed biosynthesis under some conditions, cellular NAD+ levels are dynamic rather than fixed. Enzyme affinity and local synthesis also influence how much NAD+ is available for signaling.
NAD+ is a dinucleotide composed of adenine, ribose, and nicotinamide moieties linked by phosphate groups. Its oxidized form carries a positive charge on the nicotinamide ring, which enables reversible hydride transfer. The molecule functions as a coenzyme in oxidoreductase reactions rather than as a dietary vitamin in its intact form. Cells maintain separate pools in cytoplasm, mitochondria, and nucleus. This compartmentalization allows distinct redox environments while preserving a shared chemical identity.
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.
== Diagnosis == Epidemiologically, the disorder usually develops slowly and is mainly observed in people over the age of 50. Diagnosis is made on the basis of bone marrow biopsy. Fibrosis grade 2 or 3 defines overt PMF whereas grade 0 or 1 defines prefibrotic primary myelofibrosis. A physical exam of the abdomen may reveal enlargement of the spleen, the liver, or both. Bone marrow biopsy shows fibrosis of the bone marrow. In early stages, this fibrosis is characterised by scattered linear reticulin fibres.
== Overdose == Buspirone appears to be relatively benign in cases of single-drug overdose, although no definitive data on this subject appear to be available. In one clinical trial, buspirone was administered to healthy male volunteers at a dosage of 375 mg/day, and produced side effects including nausea, vomiting, dizziness, drowsiness, miosis, and gastric distress. In early clinical trials, buspirone was given at dosages even as high as 2,400 mg/day, with akathisia, tremor, and muscle rigidity observed. Deliberate overdoses with 250 mg and up to 300 mg buspirone have resulted in drowsiness in about 50% of individuals. One death has been reported in a co-ingestion of 450 mg buspirone with alprazolam, diltiazem, alcohol, and cocaine.
== History == In November 2023, the US Food and Drug Administration (FDA) granted the application for the chikungunya vaccine with fast track, breakthrough therapy, and priority review designations. The vaccine, Ixchiq, was licensed to Valneva Austria GmbH. It contains the live attenuated chikungunya virus (CHIKV) Δ5nsP3 strain of the ECSA/IOL genotype. Ixchiq was authorized for medical use in the European Union in June 2024. A second vaccine, Vimkunya, manufactured by Bavarian Nordic, was authorized for medical use in the European Union in February 2025. In June 2026, the European Medicines Agency (EMA) recommended that the chikungunya vaccine Ixchiq should be restricted to individuals with a high risk of becoming infected with the chikungunya virus. This restriction is due to serious adverse events reported with the vaccine, including aseptic meningitis. Some of these events resulted in hospitalisation and death.
A wobble base pair is a pairing between two nucleotides in RNA molecules that does not follow Watson–Crick base pair rules. The four main wobble base pairs are guanine–uracil (G–U), hypoxanthine–uracil (I–U), hypoxanthine–adenine (I–A), and hypoxanthine–cytosine (I–C). In order to maintain consistency of nucleic acid nomenclature, "I" is used for hypoxanthine because hypoxanthine is the nucleobase of inosine; nomenclature otherwise follows the names of nucleobases and their corresponding nucleosides (e.g., "G" for both guanine and guanosine – as well as for deoxyguanosine). The thermodynamic stability of a wobble base pair is comparable to that of a Watson–Crick base pair. Wobble base pairs are fundamental in RNA secondary structure and are critical for the proper translation of the genetic code.
There are also the testimonies of Raymond Queneau (1903–1976), born in Le Havre, the city served as a framework for his novel Un rude hiver (A harsh winter) (1939). The plot of Une maison soufflée aux vents (A house blown to the winds) by Émile Danoën, winner of the Popular Novel Prize in 1951, and its sequel Idylle dans un quartier muré (Idyll in a walled neighbourhood) were located in Le Havre during the Second World War. Under the name Port de Brume Le Havre is the setting for three other novels by this author: Cerfs-volants (Kites), L'Aventure de Noël (The Adventure at Christmas), and La Queue à la pègre (Queue to the underworld). Michel Leiris wrote De la littérature considérée comme une tauromachie (Of literature considered like a bullfight) in December 1945. Diana Gabaldon set the second novel in her Outlander series, Dragonfly in Amber (1992), partly in Le Havre. Two mystery novels take place in Le Havre: Le Bilan Maletras (The Maletras Balance) by Georges Simenon and Le Crime de Rouletabille (Crime at the Roulette table) by Gaston Leroux. In Rouge Brésil (Red Brazil), winner of the Goncourt Prize in 2001, Jean-Christophe Rufin describes Le Havre in the 16th century as the port of departure of French expeditions to the New World: the hero Villegagnon leaves of the port to conquer new lands for the French crown which become Brazil. Martine–Marie Muller tells the saga of a clan of Stevedores from Le Havre in the 1950s to the 1970s in Quai des Amériques (Quay of the Americas).
Sources: en.wikipedia.org
Alkylglycerone phosphate synthase (EC 2.5.1.26, alkyldihydroxyacetonephosphate synthase, alkyldihydroxyacetone phosphate synthetase, alkyl DHAP synthetase, alkyl-DHAP, dihydroxyacetone-phosphate acyltransferase, DHAP-AT) is an enzyme associated with Type 3 Rhizomelic chondrodysplasia punctata. This enzyme catalyses the following chemical reaction
The minerals, results of biomineralization processes regulated by the environment or bacteria, are also essential components of the exopolysaccharides. They provide structural integrity to biofilm matrix and act as a scaffold to protect bacterial cells from shear forces and antimicrobial chemicals. The minerals in EPS were found to contribute to morphogenesis of bacteria and the structural integrity of the matrix. For example, in Bacillus subtilis, Mycobacterium smegmatis, and Pseudomonas aeruginosa biofilms, calcite (CaCO3) contributes to the integrity of the matrix. The minerals also associate with medical conditions. In the biofilms of Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri, the minerals calcium and magnesium cause catheter encrustation.
The cabal produced a 200-page design document detailing nearly every aspect of the game. They also produced a 30-page document for the narrative, and hired the science fiction novelist Marc Laidlaw to help manage the script. Laidlaw said his contribution was to add "old storytelling tricks" to the team's ambitious designs: "I was in awe of [the team]. It felt to me like I was just borrowing from old standards while they were the ones doing something truly new." Rather than dictate narrative elements "from some kind of ivory tower of authorial inspiration", he worked with the team to improvise ideas, and was inspired by their experiments. For example, he conceived the opening train ride after an engineer implemented train code for another concept. Valve initially planned to use traditional cutscenes, but switched to a continuous first-person perspective for lack of time. Laidlaw said they discovered unexpected advantages in this approach, as it created a sense of immersion and enforced a sense of loneliness in a frightening environment. Laidlaw felt that non-player characters were unnecessary to guide players if the design had sufficiently strong "visual grammar", and that this allowed the characters to "feel like characters instead of signposts". An early version of Half-Life began immediately after the disaster, with the environments already wrecked. Laidlaw worked with Johnson to create versions of the lab environment before the disaster to help set the story.
It is approved as an antimanic and antiseizure in Japan as well. In UK, valproate is approved for bipolar mania and epilepsy, and both valproate and divalproex are approved, although divalproex sodium is known as valproate semisodium. Valproate's precise mechanism of action is unclear. Proposed mechanisms include affecting GABA levels, blocking voltage-gated sodium channels, inhibiting histone deacetylases, and increasing LEF1. Valproic acid is a branched short-chain fatty acid (SCFA), a derivative of valeric acid. Valproate was originally synthesized in 1881 and came into medical use in 1962. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2023, it was the 160th most commonly prescribed medication in the United States, with more than 3 million prescriptions.
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 an oxidized dinucleotide coenzyme that carries electrons in metabolic reactions. It is also consumed by signaling enzymes, including sirtuins and PARPs. Its reduced form is NADH.