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.
Updated 2025-12-27. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
In glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation, NAD+ is reduced to NADH at specific dehydrogenase steps. NADH then delivers electrons to the mitochondrial electron transport chain, mainly at complex I, supporting oxidative phosphorylation and ATP production. The balance between NAD+ and NADH, often expressed as a ratio, influences metabolic flux and redox homeostasis in different cellular compartments. Cytosolic and mitochondrial pools are connected but not identical, and their ratios can differ substantially because of compartment-specific enzymes and transport systems.
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.
| 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 |
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.
== Diagnosis == The disease may be diagnosed based on a clinical examination, which identifies signs and symptoms generally associated with the people who have the condition. Genetic testing for known pathological variants is preferred, by testing of the COL6A1, COL6A2, COL6A3 and COL12A1 genes. In the case of a VUS, testing of dermal fibroblast culture is used for an accurate diagnosis. Additional laboratory tests may be performed before genetic testing, such as creatine kinase (CK) blood test, MRI of the muscles, and electromyography (EMG). Phenotypes of overlap between Ullrich congenital muscular dystrophy (UCMD) and Bethlem can be assumed. In the differential diagnosis of UCMD, even in patients without finger contractures, Bethlem myopathy could be considered.
=== Musculoskeletal === Musculoskeletal symptoms include hyperflexible joints that are unstable and prone to sprain, dislocation, subluxation, and hyperextension. As a result of frequent tissue injury, there can be an early onset of advanced osteoarthritis, chronic degenerative joint disease, swan-neck deformity of the fingers, and Boutonniere deformity of the fingers. Tendon and ligament laxity offer minuscule protection from tearing in muscles and tendons, but these problems persist. Deformities of the spine, such as scoliosis (curvature of the spine), kyphosis (a thoracic hump), tethered spinal cord syndrome, craniocervical instability (CCI), and atlantoaxial instability may also be present. Osteoporosis and osteopenia are also associated with EDS and symptomatic joint hypermobility. There can also be myalgia (muscle pain) and arthralgia (joint pain), which may be severe and disabling. Trendelenburg's sign is often seen, which means that when standing on one leg, the pelvis drops on the other side. Osgood–Schlatter disease, a painful lump on the knee, is common as well. In infants, walking can be delayed (beyond 18 months of age), and bottom-shuffling instead of crawling occurs.
== Notable works == The Saxxy awards were given to a total of 33 winners, ranging from comedic or action shorts to extended short films across a variety of genres. Longer films produced with the software include Darkest Days, an hour-long jukebox musical based on Left 4 Dead 2, and Emesis Blue, a 108-minute psychological horror feature film based on Team Fortress 2.
Sources: en.wikipedia.org
Minerals are generally oxidized derivatives of metals. Iron is mined as ores such as magnetite (Fe3O4) and hematite (Fe2O3). Titanium is mined as its dioxide, usually in the form of rutile (TiO2). These oxides must be reduced to obtain the corresponding metals, often achieved by heating these oxides with carbon or carbon monoxide as reducing agents. Blast furnaces are the reactors where iron oxides and coke (a form of carbon) are combined to produce molten iron. The main chemical reaction producing the molten iron is:
In November 1949, Pauling, Harvey Itano, S. J. Singer and Ibert Wells published "Sickle Cell Anemia, a Molecular Disease" in the journal Science. It was the first proof of a human disease being caused by an abnormal protein, and sickle cell anemia became the first disease understood at the molecular level. (It was not, however, the first demonstration that variant forms of hemoglobin could be distinguished by electrophoresis, which had been shown several years earlier by Maud Menten and collaborators). Using electrophoresis, they demonstrated that individuals with sickle cell disease have a modified form of hemoglobin in their red blood cells, and that individuals with sickle cell trait have both the normal and abnormal forms of hemoglobin. This was the first demonstration causally linking an abnormal protein to a disease, and also the first demonstration that Mendelian inheritance determines the specific physical properties of proteins, not simply their presence or absence – the dawn of molecular genetics. His success with sickle cell anemia led Pauling to speculate that a number of other diseases, including mental illnesses such as schizophrenia, might result from flawed genetics. As chairman of the Division of Chemistry and Chemical Engineering and director of the Gates and Crellin Chemical Laboratories, he encouraged the hiring of researchers with a chemical-biomedical approach to mental illness, a direction not always popular with established Caltech chemists. In 1951, Pauling gave a lecture entitled "Molecular Medicine".
== Signs and symptoms == MODY accounts for at least 1-5% of all diagnoses of diabetes mellitus, though 50-90% of cases are estimated to be misdiagnosed as type 1, or type 2 diabetes. Estimated prevalence rates indicate 1 per 10,000 in adults, and 1 per 23,000 in children. 50% of first-degree relatives will inherit the same mutation, giving them a greater than 95% lifetime risk of developing MODY themselves. For this reason, correct diagnosis of this condition is important. Typically patients present with a strong family history of diabetes (i.e.: presence of diabetes before the age of 25 in two consecutive generations). There are two general types of clinical presentation.
Sources: en.wikipedia.org
== History == Vitacost began operations in 1994 as a catalog retailer of third-party vitamins and supplements under the name Nature's Wealth Company by its founder Wayne Gorsek. In 1999, the company launched Vitacost.com and introduced proprietary vitamins and supplements, which has since expanded to include food, beauty products and sports nutrition. The company completed construction of a manufacturing facility located in Lexington, North Carolina, in 2008. Effective September 1, 2012, Vitacost agreed to lease its manufacturing facilities to a third-party provider. On September 23, 2009, Vitacost went public. Vitacost shares traded on the NASDAQ were suspended on December 7, 2010, for financials not adding up. By the time the stock was reinstated by NASDAQ, the stock had lost most of its value with investors losing almost all of their investment. ("Gebben"). During 2010, the company expanded and upgraded its West Coast distribution facility located in Las Vegas, Nevada. The Company began a similar project for its east coast distribution center, located in Lexington, North Carolina in the spring of 2010, with the building construction completed in the first quarter of 2011. Gorsek was found guilty of securities fraud on January 28, 2003. The SEC Commission announced on this day that the Honorable Jeanne E. Scott, U.S. District Judge for the Central District of Illinois, has found two former brokers and stock promoters, Wayne F. Gorsek ("Gorsek") and Lyndell F.
==== Eliminated in primary ==== Rob Altman, U.S. Army veteran Ben Bius, businessman, candidate for Texas's 12th House of Representatives district in 2022 and 2024, and nominee in 2000 Rob Brown, pastor (previously ran in the 17th district) Brandon Hawbraker, software engineer Jessica Karlsruher, lobbyist (previously filed to run in the 21st district) Kara King, mayor of Bee Cave Scott MacLeod, U.S. Army veteran Jenny Garcia Sharon, volunteer caregiver Jeremy Story, minister
=== Sphincters === The esophagus is surrounded at the top and bottom by two muscular rings, known respectively as the upper esophageal sphincter and the lower esophageal sphincter. These sphincters act to close the esophagus when food is not being swallowed. The upper esophageal sphincter is an anatomical sphincter, which is formed by the lower portion of the inferior pharyngeal constrictor, also known as the cricopharyngeal sphincter due to its relation with cricoid cartilage of the larynx anteriorly. However, the lower esophageal sphincter is not an anatomical but rather a functional sphincter, meaning that it acts as a sphincter but does not have a distinct thickening like other sphincters. The upper esophageal sphincter surrounds the upper part of the esophagus. It consists of skeletal muscle but is not under voluntary control. Opening of the upper esophageal sphincter is triggered by the swallowing reflex. The primary muscle of the upper esophageal sphincter is the cricopharyngeal part of the inferior pharyngeal constrictor. The lower esophageal sphincter, or gastroesophageal sphincter, surrounds the lower part of the esophagus at the gastroesophageal junction between the esophagus and the stomach. It is also called the cardiac sphincter or cardioesophageal sphincter, named from the adjacent part of the stomach, the cardia. Dysfunction of the gastroesophageal sphincter causes gastroesophageal reflux, which causes heartburn, and, if it happens often enough, can lead to gastroesophageal reflux disease, with damage of the esophageal mucosa.
(C4H2NH)n + 0.2 X → [(C4H2NH)nX0.2] The polymerization and p-doping can also be effected electrochemically. The resulting conductive polymer are peeled off of the anode. Cyclic voltammetry and chronocoulometry methods can be used for electrochemical synthesis of polypyrrole. Most recent micro and nano droplet researches have been conducted in the synthesis of polypyrrole microstructures using various fluid templates formed on different solid surfaces.
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.