The short version of coenzyme fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-06-12 and is reviewed periodically as new material appears.
Related compounds include NADH, the reduced form, and NADP+, which carries an additional phosphate group. NADP+ and NADPH often serve in biosynthetic and antioxidant reactions, while NAD+ and NADH are more associated with energy-yielding catabolism. Nicotinamide, nicotinic acid, and nicotinamide riboside are precursors that can enter salvage pathways. The exact contribution of dietary precursors to tissue NAD+ pools is an area of active investigation. Some studies measure labeled precursors to trace those routes.
NAD+ is the oxidized form of nicotinamide adenine dinucleotide, a coenzyme built from two nucleotides joined by a phosphate linkage. One nucleotide carries adenine, and the other carries nicotinamide; the plus sign denotes a formal positive charge on the nicotinamide ring, not a free proton. In cells, NAD+ and its reduced partner NADH form a reversible redox pair. That pair participates in electron transfer reactions throughout metabolism. The abbreviation NAD+ is common in biochemistry, while NAD(H) sometimes denotes the combined pool.
The molecule was first described in the early twentieth century as a factor that promoted fermentation in yeast extracts. Later work linked it to hydrogen transfer and to the oxidation of nutrients in living tissues. Its structure was resolved as a dinucleotide, which explained why it could accept and donate electrons at specific enzyme sites. Today, NAD+ is recognized as a central substrate and signaling precursor, not merely a metabolic cofactor. Whether all observed NAD+ changes reflect causal signaling remains an open question.
Research on NAD+ often examines changes with age, diet, exercise, and disease states, but causal relationships are difficult to establish. Some studies measure NAD+ levels, while others assess enzyme activity or downstream markers. In the literature, terms such as "NAD+ decline" and "NAD+ boosting" appear in both scientific and commercial contexts, sometimes without precise definitions. Whether changes in measured NAD+ directly produce health effects remains an open question. Results from cells, animals, and humans cannot be assumed to translate directly.
Measuring NAD+ in biological samples requires rapid processing because the compound can degrade or interconvert after collection. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and mass spectrometry. Each method has different sensitivity, specificity, and susceptibility to interference from related nucleotides. Sample type matters: cultured cells, animal tissues, and human blood present distinct challenges. Reported values can vary widely across laboratories because of differences in extraction, normalization, and analytical platform. Standardization remains an open issue in the field.
| Property | Value | Notes |
|---|---|---|
| Chemical name | Nicotinamide adenine dinucleotide (oxidized form) | NAD+ denotes the oxidized redox state |
| Common synonyms | Diphosphopyridine nucleotide; coenzyme I | Older names appear in historical literature |
| Molar mass | About 663.43 g/mol | Free acid value; salts and hydrates differ |
| Appearance | White to off-white powder | The purified solid is white; solutions are clear |
| Solubility | Highly soluble in water | Aqueous buffers are common laboratory solvents |
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.
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.
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.
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.
While in Constantine's treatise Liber de Coitu, the clitoris is referred to a few times, Magnus gave an equal amount of attention to male and female organs. Like Avicenna, Magnus also used the word virga for the clitoris, but employed it for the male and female genitals; despite his efforts to give equal ground to the clitoris, the cycle of suppression and rediscovery of the organ continued, and a 16th-century justification for clitoridectomy appears to have been confused with intersex conditions and the imprecision created by the word nymphae substituted for the word clitoris. Nymphotomy was a medical operation to excise an unusually large clitoris, but what was considered "unusually large" was often a matter of perception. The procedure was routinely performed on Egyptian women, due to physicians such as Jacques Daléchamps who believed that this version of the clitoris was "an unusual feature that occurred in almost all Egyptian women [and] some of ours, so that when they find themselves in the company of other women, or their clothes rub them while they walk or their husbands wish to approach them, it erects like a male penis and indeed they use it to play with other women, as their husbands would do ... Thus the parts are cut".
Muscle cells work by detecting a flow of electrical impulses from the brain, which signals them to contract through the release of calcium by the sarcoplasmic reticulum. Fatigue (reduced ability to generate force) may occur due to the nerve, or within the muscle cells themselves. New research from scientists at Columbia University suggests that muscle fatigue is caused by calcium leaking out of the muscle cell. This makes less calcium available for the muscle cell. In addition, the Columbia researchers propose that an enzyme activated by this released calcium eats away at muscle fibers. Substrates within the muscle generally serve to power muscular contractions. They include molecules such as adenosine triphosphate (ATP), glycogen and creatine phosphate. ATP binds to the myosin head and causes the 'ratchetting' that results in contraction according to the sliding filament model. Creatine phosphate stores energy so ATP can be rapidly regenerated within the muscle cells from adenosine diphosphate (ADP) and inorganic phosphate ions, allowing for sustained powerful contractions that last between 5–7 seconds. Glycogen is the intramuscular storage form of glucose, used to generate energy quickly once intramuscular creatine stores are exhausted, producing lactic acid as a metabolic byproduct. Contrary to common belief, lactic acid accumulation doesn't actually cause the burning sensation felt when people exhaust their oxygen and oxidative metabolism, but in actuality, lactic acid in presence of oxygen recycles to produce pyruvate in the liver, which is known as the Cori cycle.
=== Canada === In 2026, cottage cheese consumption increased by 15-20% over market levels in recent years, causing a supply shortage in some regions. In 2025, 35,459 tonnes (78,174,000 lb) of cottage cheese were produced in Canada. The Canadian Dairy Commission maintains consumer guidelines and standards for quality manufacturing of cottage cheese.
Hydrogenases are subclassified into three different types based on the active site metal content: iron–iron hydrogenase, nickel–iron hydrogenase, and iron hydrogenase. All hydrogenases catalyze reversible H2 uptake, but while the [FeFe] and [NiFe] hydrogenases are true redox catalysts, driving H2 oxidation and H+ reduction
The emergence of guerrilla warfare and acts of urban insurrection by the black nationalist parties in Rhodesia allowed racial politics to be elevated into an issue of law and order in white Rhodesian public discourse. To Smith and his government, black nationalists were stateless dissidents whose primary motives were not political, but crime and perpetuating lawlessness; for example, Smith preferred to describe the insurgents as "gangsters" in his commentary. The use of weapons and explosives sourced from communist states by the black nationalists also disguised the racial dynamics of the conflict, allowing white Rhodesians to claim that they were targets of Soviet-directed communist agitators rather than a domestic political movement. Smith and his supporters perceived themselves as collective defenders of the traditional values of the British Empire against the twin threats of international communism, manifested through the Soviet Union's support for black nationalist militants, and the social and political decadence of the West. Often repeated appeals to the Christian heritage of their pioneer ancestors in "defending the free world" and sustaining "Western civilisation" reflected these beliefs. This was hardly an unusual opinion among white minorities in Southern Africa at the time; a dossier compiled by United States intelligence officials on the topic found that:
Sources: en.wikipedia.org
=== Free thyroxine === Free thyroxine (fT4 or free T4) is generally elevated in hyperthyroidism and decreased in hypothyroidism. Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are:
=== Off-label drugs === Antihistamines (histamine H1 receptor antagonists) (e.g., cetirizine, desloratadine, fexofenadine, levocetirizine, loratadine) Corticosteroids (corticosteroid receptor agonists) (e.g., hydrocortisone, prednisone, triamcinolone acetonide) Hydroquinone – tyrosinase inhibitor and skin-lightening agent Nicotinamide (niacinamide) – vitamin B3 Oral antiandrogens (androgen receptor antagonists) (e.g., spironolactone, cyproterone acetate, flutamide, bicalutamide, ketoconazole, cimetidine) Other antibiotics (e.g., erythromycin, metronidazole, sulfacetamide) Other ethinylestradiol-containing combined oral contraceptives Salicylic acid – various actions (keratolytic, comedolytic, and bacteriostatic) Zinc – undefined mechanism of action (antibacterial and anti-inflammatory)
The two substrates of this enzyme are 2-dehydro-3-deoxy-D-gluconic acid and oxidised nicotinamide adenine dinucleotide (NAD+). Its products are (4S)-4,6-dihydroxy-2,5-dioxohexanoic acid, reduced NADH, and a proton. This enzyme participates in pentose and glucuronate interconversions.
=== Energy === Schleswig-Holstein is a leader in the country's growing renewable energy industry. In 2014, Schleswig-Holstein became the first German state to cover 100% of its electric power demand with renewable energy sources (chiefly wind 70%, solar 3.8%, and biomass 8.3%). By 2023, according to Schleswig-Holstein Netz, renewable energy sources were providing 204% of Schleswig-Holstein's electricity demand (the 104% surplus are exports). The largest German oil field Mittelplate is located in the North Sea off the Dithmarsch coast and connected with a refinery in Hemmingstedt and chemical plants in Brunsbüttel via pipeline. It produces ca. 1.4 million tonnes of oil annually.
In 1865 the German chemist Adolf von Baeyer began working on the synthesis of indigo. He described his first synthesis of indigo in 1878 (from isatin) and a second synthesis in 1880 (from 2-nitrobenzaldehyde). (It was not until 1883 that Baeyer finally determined the structure of indigo.) The synthesis of indigo remained impractical, so the search for alternative starting materials at Badische Anilin- und Soda-Fabrik (BASF) and Hoechst continued. In 1890, Dr Flimm of Darmstadt, Germany, discovered a simple method for synthesizing indigo with a derivative of acetanilide using caustic potash. This reaction produced a blue compound chemically identical to natural indigo that was identified by its reactions and absorption spectrum. This publication of independent dye synthesis experiments in scientific journals during this period demonstrates that the production of synthetic indigo was a widely pursued goal in industrial chemistry well before BASF's successful market launch. By 1897, BASF had developed an economically viable synthesizing process that replaced natural plant production. Earlier attempts to replace plant-based production were ineffective on an industrial scale. Johannes Pfleger and Karl Heumann eventually came up with industrial mass production synthesis. The synthesis of N-(2-carboxyphenyl)glycine from the easy to obtain aniline provided a new and economically attractive route. BASF developed a commercially feasible manufacturing process that was in use by 1897, at which time 19,000 tons of indigo were being produced from plant sources.
Sources: en.wikipedia.org
It indicates a formal positive charge on the nicotinamide ring. The molecule is not simply a protonated acid, and the charge is part of its redox chemistry.
NAD+ is the oxidized form, while NADH is the reduced form carrying two additional electrons and a proton. The two forms interconvert in many metabolic reactions.
No. NADP+ contains an extra phosphate group on the adenine ribose. NADP+ and NADPH tend to participate in different biosynthetic and antioxidant pathways.
Researchers often use enzymatic cycling assays, liquid chromatography, or mass spectrometry. The choice depends on sample size, sensitivity needs, and available equipment. Because NAD+ can degrade quickly, rapid extraction and careful handling are important.