A practical reference on redox carrier: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-01-03 and is reviewed periodically as new material appears.
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.
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.
NAD+ is a dinucleotide composed of adenine, ribose, and nicotinamide groups joined by phosphate linkages. It serves as a coenzyme in oxidoreductase reactions, cycling between oxidized NAD+ and reduced NADH. The molecule is water-soluble and occurs in all living cells. Its nicotinamide ring accepts hydride ions during catabolic reactions, linking substrate oxidation to electron transport. This redox couple supports ATP production and helps maintain cytosolic and mitochondrial redox balance in many cell types.
Beyond redox catalysis, NAD+ is a substrate for enzymes that transfer ADP-ribose or remove acetyl groups from proteins. Sirtuins and poly(ADP-ribose) polymerases consume NAD+ and release nicotinamide as a byproduct. These reactions connect cellular energy status to gene regulation, DNA repair, and stress responses. Because NAD+ is used rather than merely recycled in such signaling, its concentration reflects both biosynthesis and consumption. The balance between salvage and de novo synthesis pathways determines available pools in different tissues.
| Property | Value | Notes |
|---|---|---|
| Chemical formula | C21H27N7O14P2 | Oxidized free acid form; charge depends on pH. |
| Molar mass | 663.43 g/mol | Calculated for the free acid. |
| CAS Registry Number | 53-84-9 | For the anhydrous free acid; salts have different identifiers. |
| Appearance | White to off-white powder | Solid material; hygroscopic. |
| Solubility | Water-soluble | Dissolves in aqueous buffers; solubility varies with pH and salt. |
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.
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 transfer ADP-ribose or remove acetyl groups. Sirtuins, PARPs, and CD38-family enzymes consume NAD+ and produce nicotinamide and ADP-ribose-related products. These reactions link NAD+ availability to DNA repair, chromatin modification, and cellular signaling. Because the molecule is central to energy metabolism and regulation, changes in its concentration are studied in aging, immunity, and metabolic research. The balance between synthesis and consumption varies by tissue, developmental stage, and physiological state.
In humans, NAD+ can be synthesized from nicotinic acid, nicotinamide, nicotinamide riboside, and tryptophan through overlapping pathways. The salvage pathway recycles nicotinamide back to NAD+ and is often considered a major route in many tissues. Dietary precursors and intracellular recycling both contribute to the pool, but the quantitative importance of each source remains an active research question. NAD+ levels are not uniform across organs or cell compartments. Measurements in blood do not necessarily reflect concentrations inside tissues.
== History == Spontaneous vertebral artery dissection was described in the 1970s. Prior to this, there had been isolated case reports about carotid dissection. In 1971, C. Miller Fisher, a Canadian neurologist and stroke physician working at Massachusetts General Hospital, first noted the "string sign" abnormality in carotid arteries on cerebral angiograms of stroke patients, and subsequently discovered that the same abnormality could occur in the vertebral arteries. He reported the discovery in a paper in 1978.
=== Agitation === Lorazepam is sometimes used as an alternative to haloperidol when there is the need for rapid sedation of violent or agitated individuals. Haloperidol plus promethazine is preferred due to better effectiveness and due to lorazepam's adverse effects on respiratory function. Adverse effects such as behavioral disinhibition may make benzodiazepines inappropriate for some people who are acutely psychotic. Acute delirium is sometimes treated with lorazepam, but as it can cause paradoxical effects, it is preferably given together with haloperidol. Lorazepam is absorbed relatively slowly if given intramuscularly, a common route in restraint situations.
In 1965, Francisco Condom was elected Grand Master. Leadership stabilized, but membership fell. From 1959 to 1980, membership in Freemasonry in Cuba declined by 40% in a period of sharp and intense reduction. Where in 1959, there were over 34,000 Freemasons, in 1980, that number had fallen to below 20,000. US narratives attributed this decline to a mistrust that the Communist regime held of Freemasonry, Cuban narratives attributed this to the economic impact that the Revolution had on the upper and middle classes, which had previously been the bulk of Freemasons in Cuba, and the former barriers to entry that existed for those in the working class. Cuba's most prominent economic trading partners were the Soviet Union and the Eastern Bloc coalition, where Freemasonry had been entirely outlawed since the time of the Bolsheviks. Castro desired to maintain positive relations with Cuba's primary economic benefactors, and to avoid a political scandal, he did not see any use of Freemasonry as a tool in Cuba's foreign policy. Additionally, in those impoverished countries where Cuba desired to spread its brand of Marxism, Freemasonry had long been seen as a gentlemen's club for colonizers. Castro therefore limited international travel for Freemasons. From 1960 to 1980, due to a negative societal stereotype about the working character of Freemasonry, if Freemasons were discovered, they struggled to maintain positions at university and trade schools, secure employment, or be promoted at work. On March 28, 1965, Francisco M.
Sources: en.wikipedia.org
The Yucatec, who came from Yucatán, Mexico, to escape the violent Caste War of the 1840s. The Mopan, who are indigenous to Belize but were forced out to Guatemala by the British for raiding settlements. They returned to Belize to evade enslavement by the Guatemalans in the 19th century. The Q'eqchi', who also fled from slavery in Guatemala in the 19th century. The latter groups are chiefly found in the Toledo District. The Maya speak their native languages and Spanish, and are also often fluent in English and Belizean Creole.
== Diagnosis == In order to diagnose paraneoplastic pemphigus, several tests may be performed. Initially, samples are obtained via skin biopsy for routine microscopy and direct immunofluorescence (DIF) testing. The skin sample needs to be obtained from an unaffected area adjacent to a lesion. Testing in more detail follows depending on the results from the DIF. Prompt diagnosis of PNP is crucial due to the high mortality rate of the disease.
=== Chloroplast inheritance === Like mitochondria, chloroplasts are usually inherited from a single parent. Biparental chloroplast inheritance—where plastid genes are inherited from both parent plants—occurs in very low levels in some flowering plants. Many mechanisms prevent biparental chloroplast DNA inheritance, including selective destruction of chloroplasts or their genes within the gamete or zygote, and chloroplasts from one parent being excluded from the embryo. Parental chloroplasts can be sorted so that only one type is present in each offspring. Gymnosperms, such as pine trees, mostly pass on chloroplasts paternally, while flowering plants often inherit chloroplasts maternally. Flowering plants were once thought to only inherit chloroplasts maternally. However, there are now many documented cases of angiosperms inheriting chloroplasts paternally. Angiosperms, which pass on chloroplasts maternally, have many ways to prevent paternal inheritance. Most of them produce sperm cells that do not contain any plastids. There are many other documented mechanisms that prevent paternal inheritance in these flowering plants, such as different rates of chloroplast replication within the embryo. Among angiosperms, paternal chloroplast inheritance is observed more often in hybrids than in offspring from parents of the same species. This suggests that incompatible hybrid genes might interfere with the mechanisms that prevent paternal inheritance.
Sources: en.wikipedia.org
NAD+ is a coenzyme found in living cells and is the oxidized form of nicotinamide adenine dinucleotide. It accepts electrons in redox reactions and also serves as a substrate for certain signaling and repair enzymes.
NAD+ becomes NADH when it accepts a hydride ion during oxidation-reduction reactions. NADH then donates electrons to other molecules, after which the carrier can return to the NAD+ form.
No, nicotinamide is a smaller molecule and a component of NAD+. Cells can use nicotinamide to rebuild NAD+ through the salvage pathway.
NAD+ is the oxidized form and NADH is the reduced form of the same coenzyme. NAD+ accepts electrons during oxidation reactions, becoming NADH, which can donate electrons in other reactions. The ratio between them helps describe a cell's redox state.