A practical reference on Sirtuins: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-11-09. Anything still debated is marked as such rather than presented as settled.
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 |
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.
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.
In redox reactions, NAD+ accepts a hydride ion, which consists of two electrons and one proton. The hydride adds to the nicotinamide ring at a specific carbon, converting NAD+ into NADH. Dehydrogenase enzymes use this step in glycolysis, the citric acid cycle, and fatty acid oxidation. NADH later donates electrons to the mitochondrial electron transport chain, helping to drive ATP synthesis. The balance between NAD+ and NADH reflects the metabolic state of a cell, and shifts in that balance can alter how pathways operate.
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.
=== Spinal disc disease === Spinal disc disease occurs when the nucleus pulposus, a gel-like material in the inner core of the vertebral disc, ruptures. Rupturing of the nucleus pulposus can lead to compression of nerve roots. Symptoms may be unilateral or bilateral, and correlate to the region of the spine affected. The most common region for spinal disk disease is at L4–L5 or L5–S1. The risk for lumbar disc disease is increased in overweight individuals because of the increased compressive force on the nucleus pulposus, and is twice as likely to occur in men. A 2002 study found that lifestyle factors such as night-shift work and lack of physical activity can also increase the risk of lumbar disc disease. Severe spinal-cord compression is considered a surgical emergency and requires decompression to preserve motor and sensory function. Cauda equina syndrome involves severe compression of the cauda equina and presents initially with pain followed by motor and sensory dysfunction. Bladder incontinence is seen in later stages of cauda equina syndrome.
== Ion gating == A Bradbury–Nielsen shutter is a type of ion gate used in TOF mass spectrometers and in ion mobility spectrometers, as well as Hadamard transform TOF mass spectrometers. The Bradbury–Nielsen shutter is ideal for fast timed ion selector (TIS)—a device used for isolating ions over narrow mass range in tandem (TOF/TOF) MALDI mass spectrometers.
=== Rise of the galactic city === The term "galactic city", associated with Lewis Mumford, describes a dispersed form of metropolitan development. Twentieth-century urban growth in parts of the United States was supported by several infrastructure and technological changes, including highway transportation, air conditioning, expanded agricultural production and systems for transporting and storing food over long distances. Refrigeration contributed to this broader infrastructure by allowing urban populations to obtain perishable food from distant agricultural regions rather than depending primarily on nearby production. In analyses of settlement patterns, refrigeration has therefore been identified as one of several technologies that reduced constraints on population growth in locations distant from traditional agricultural and transport centres.
Similarly, accumbal G9a hyperexpression results in markedly increased histone 3 lysine residue 9 dimethylation (H3K9me2) and blocks the induction of ΔFosB-mediated neural and behavioral plasticity by chronic drug use, which occurs via H3K9me2-mediated repression of transcription factors for ΔFosB and H3K9me2-mediated repression of various ΔFosB transcriptional targets (e.g., CDK5). ΔFosB also plays an important role in regulating behavioral responses to natural rewards, such as palatable food, sex, and exercise. Since both natural rewards and addictive drugs induce the expression of ΔFosB (i.e., they cause the brain to produce more of it), chronic acquisition of these rewards can result in a similar pathological state of addiction. Consequently, ΔFosB is the most significant factor involved in both amphetamine addiction and amphetamine-induced sexual addictions, which are compulsive sexual behaviors that result from excessive sexual activity and amphetamine use. These sexual addictions are associated with a dopamine dysregulation syndrome which occurs in some patients taking dopaminergic drugs. The effects of amphetamine on gene regulation are both dose- and route-dependent. Most of the research on gene regulation and addiction is based upon animal studies with intravenous amphetamine administration at very high doses. The few studies that have used equivalent (weight-adjusted) human therapeutic doses and oral administration show that these changes, if they occur, are relatively minor.
== History == ARUP was founded by John Matsen and Carl Kjeldsberg, based on Lloyd Martin's vision of an independent, not-for-profit laboratory owned by the Department of Pathology. ARUP's facilities operate with a high degree of automation. Their 65 laboratories include sorters, automated thawing and mixing, and house a two-story automated lab specimen freezer. The freezer can store 2.3 million specimens and retrieve a specimen in 2.5 minutes. In 2003, ARUP partnered with the Utah Department of Health to create a pilot program for expanding newborn screening in Utah to include an additional 30 metabolic markers. A year later, this program became the standard for the mandatory screening of all newborns in the state of Utah.
Sources: en.wikipedia.org
Benzylmorphine (Peronine) is a semi-synthetic opioid narcotic introduced to the international market in 1896 and that of the United States very shortly thereafter. It is much like codeine, containing a benzyl group attached to the morphine molecule just as the methyl group creates codeine and the ethyl group creates ethylmorphine or dionine (used as a generic name for that drug just as peronine is for benzylmorphine). It is about 90% as strong as codeine by weight. This drug, the benzyl ether of morphine, should not be confused with dibenzoylmorphine, an ester of morphine comparable to heroin. Another morphine ether developed around the same time, benzyldihydromorphine, saw some clinical use in the opening years of the 20th century. The ethers of morphine and codeine as well as dihydromorphine and dihydrocodeine number close to 100 and include such obscure opioids as formylallopseudoisocodeine. Benzylmorphine is used in much the same way as codeine and ethylmorphine, primarily as a moderate strength analgesic, for eye surgery as a 1 to 2% solution, and as a cough suppressant. It was available in the United States prior to 1914 and was still used until the 1960s, but fell into disuse once alternative opiate derivatives became preferred by doctors (i.e. hydrocodone as an analgesic and codeine as a cough suppressant) Benzylmorphine is now a Schedule I Controlled Substance in the US and is regulated internationally under UN drug conventions. Benzylmorphine is an active metabolite of the opioid analgesic myrophine, formed in the liver.
=== Analogues === Other deuterated drugs related to deudimethyltryptamine or DMT-d10 include the deuterated DMT analogue SPL028 (D2-DMT; α,α-dideutero-DMT), the deuterated psilocin analogue deupsilocin (HLP003; CYB003; d10-psilocin), and the deuterated phenethylamine HLP005 (CYB005).
==== mGluR1 and mGluR4 ==== Signal from these two receptors are conveyed in a manner independent of TRPM5. Single umami-sensitive fibres in mice are mostly either "sucrose-best" or "glutamate-best". Within each type there are two subtypes: one shows synergistic activation between monopotassium glutamate and inosine monophosphate, the other does not. The TAS1R1/3 + TRPM5 route uses the "sucrose-best" fibers with synergy, while mGluR1 and mGluR4 use both of the "glutamate-best" subtypes.
== Function == Isogenous groups differentiate into individual chondrocytes where they continue to produce and deposit extracellular matrix (ECM), lengthening the cartilage and increasing its diameter. This is termed interstitial growth and is one of only two ways cartilage can grow.
== Early life == Darren Burke was born in Halifax, Nova Scotia. He completed an undergraduate degree in Physical Education and a master's degree in Science from Dalhousie University. He was awarded a PhD in Exercise Physiology at the University of Saskatchewan in 2001 with the thesis "Individual creatine pool size and responsiveness associated with creatine supplementation".
Sources: en.wikipedia.org
=== Malta === The Parliament of Malta consists of the president of Malta and the House of Representatives of 69 members (article 51 of the Constitution), referred to as "members of Parliament" (article 52(1) of the Constitution). When appointed from outside the House, the speaker is also considered a member of the Parliament. The Constitution lists the qualifications and disqualifications from serving as a member of Parliament. Privileges of members of Parliament and their Code of Ethics are laid out in the House of Representatives (Privileges and Powers) Ordinance.
== Physiological adaptations == Xanthoria parietina regulates water balance while maintaining gas exchange, allowing it to tolerate fluctuating moisture conditions. This adaptation is largely due to the class I hydrophobin protein XPH1, which self-assembles into a hydrophobic rodlet layer on fungal hyphae in the medullary and algal layers of the thallus. The hydrophobin layer prevents waterlogging while preserving air spaces essential for CO2 and O2 diffusion. Unlike the hydrophilic outer cortex, which absorbs water, the fungal hyphae are coated with a hydrophobic barrier, ensuring continuous gas exchange even in rain or high humidity. This feature is especially beneficial in coastal and riparian environments, where frequent wetting could otherwise disrupt metabolism. The thallus structure of Xanthoria parietina consists of approximately 7% algal cells, 43% fungal tissue, 18% air spaces, and 34% extracellular matrix, which may include glucan or lichenan. The air spaces reduce CO2 diffusion resistance, improving photosynthesis even when fungal walls are water-saturated. Protein XPH1 forms a stable, insoluble coating that enhances the lichen's resilience. It contains a leucine zipper domain, likely aiding in aggregation at air-water interfaces to prevent liquid infiltration. Freeze-fracture electron microscopy reveals that the hydrophobin layer coats both fungal and algal cell walls, forming a protective boundary between symbiotic partners and the environment. In X.
=== Venture capital === Verdine has worked in the venture capital industry as a Venture Partner with Apple Tree Partners, Third Rock Ventures, and WuXi Healthcare Ventures, and as a Special Advisor to Texas Pacific Group.
In plants, algae, cyanobacteria, and phototrophic and chemoautotrophic Pseudomonadota (formerly referred to as proteobacteria), the enzyme usually consists of two types of protein subunit, called the large chain (L, about 55,000 Da) and the small chain (S, about 13,000 Da). The large-chain gene (rbcL) is encoded by the chloroplast DNA in plants. There are typically several related small-chain genes in the nucleus of plant cells, and the small chains are imported to the stromal compartment of chloroplasts from the cytosol by crossing the outer chloroplast membrane. The enzymatically active substrate (ribulose 1,5-bisphosphate) binding sites are located in the large chains that form dimers in which amino acids from each large chain contribute to the binding sites. A total of eight large chains (= four dimers) and eight small chains assemble into a larger complex of about 540,000 Da. In some Pseudomonadota and dinoflagellates, enzymes consisting of only large subunits have been found. Magnesium ions (Mg2+) are needed for enzymatic activity. Correct positioning of Mg2+ in the active site of the enzyme involves addition of an "activating" carbon dioxide molecule (CO2) to a lysine in the active site (forming a carbamate). Mg2+ operates by driving deprotonation of the Lys210 residue, causing the Lys residue to rotate by 120 degrees to the trans conformer, decreasing the distance between the nitrogen of Lys and the carbon of CO2. The close proximity allows for the formation of a covalent bond, resulting in the carbamate.
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.