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Updated 2025-09-14. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
NAD+ is a dinucleotide composed of nicotinamide, ribose, and adenine linked by phosphate groups. Its full name is nicotinamide adenine dinucleotide, with "+" denoting the oxidized form. The molecule acts as a coenzyme in redox reactions, cycling between NAD+ and NADH. In cells, it participates in electron transfer during glycolysis, the citric acid cycle, and oxidative phosphorylation. It is distinct from NADP+, which carries an additional phosphate group and supports different biosynthetic reactions.
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.
| Property | Value | Notes |
|---|---|---|
| Molar mass | 663.43 g/mol | For the free acid form; salts have higher mass. |
| Appearance | White to off-white powder | Often hygroscopic; may clump on exposure to air. |
| Solubility | Freely soluble in water | Poorly soluble in nonpolar organic solvents. |
| Typical storage | -20 °C, desiccated | Protect from light and moisture; avoid repeated freeze-thaw. |
| Common synonyms | beta-NAD, DPN | DPN stands for diphosphopyridine nucleotide, an older name. |
Quantification of NAD+ in biological samples usually relies on separation techniques coupled to sensitive detection. High-performance liquid chromatography with ultraviolet detection can measure the oxidized form by its absorbance near 260 nm, while mass spectrometry provides greater specificity and can distinguish NAD+ from close analogs. Enzymatic cycling assays use coupled dehydrogenase reactions to amplify signal and estimate NAD+ concentrations in cell or tissue extracts. Because NAD+ and NADH interconvert rapidly, sample preparation must quench metabolism quickly and preserve the redox state before analysis.
The stability of NAD+ depends on pH, temperature, light exposure, and the presence of degradative enzymes. Aqueous solutions are generally more stable under mildly acidic to neutral conditions and degrade faster under alkaline conditions or prolonged heat. The solid is hygroscopic and should be stored desiccated, often frozen, and protected from repeated freeze-thaw cycles. In laboratory handling, aliquots reduce repeated temperature changes, and chelating agents may limit metal-catalyzed hydrolysis in some buffers. These practices matter because even small amounts of NADH or hydrolysis products can interfere with quantitative assays.
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.
Beyond redox chemistry, NAD+ is consumed as a substrate by enzymes that transfer ADP-ribose or remove acetyl groups. Sirtuins use NAD+ in deacylation reactions, poly(ADP-ribose) polymerases use it in DNA damage responses, and CD38 hydrolases convert it to signaling metabolites. Because these enzymes compete for the same pool, changes in NAD+ availability can influence multiple cellular processes. The relative contribution of each consumption route differs by cell type and condition, and precise quantitative links remain an active area of study.
Research on NAD+ spans biochemistry, aging biology, and metabolism. Studies often examine how NAD+ levels change with age, diet, exercise, or disease states, and whether precursor supplementation alters those levels. Findings in animal models do not automatically translate to humans, and measurement methods vary across studies. Questions about tissue-specific effects, long-term consequences, and causal relationships remain open. NAD+ itself is not established as a single therapeutic agent with a broad clinical role.
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.
In many ectomycorrhizas the Hartig net hyphae lack internal divisions, creating a multinuclear transfer cell-like structure that facilitates interhyphal transport. The hyphae have a high concentration of organelles responsible for energy and protein production (mitochondria and rough endoplasmic reticulum) at their tips. There are signs that transporters in both fungal and plant plasma membranes are active, suggesting a bidirectional nutrient exchange.
According to Osborne, the game's maps had "imaginative texturing and dramatic lighting effects", but pointed out that they were too dark sometimes. Wolfe felt that the environmental textures were realistic enough. Critics appreciated the realistic weapon sound effects, with Osborne writing that they made guns "viscerally fun to shoot". Wolfe agreed, but wished "the same amount of attention to detail was given to the rest of the sound in the game". He felt that the crashing thunder was flat and pointed out that footsteps didn't vary based on the surface being walked on. Dodson felt that the animations were dated, but were "nothing to scoff at". Hiles commented that the character model animations needed improvement.
Gibberellins (GAs) include a large range of chemicals that are produced naturally within plants and by fungi. They were first discovered when Japanese researchers, including Eiichi Kurosawa, noticed a chemical produced by a fungus called Gibberella fujikuroi that produced abnormal growth in rice plants. It was later discovered that GAs are also produced by the plants themselves and control multiple aspects of development across the life cycle. The synthesis of GA is strongly upregulated in seeds at germination and its presence is required for germination to occur. In seedlings and adults, GAs strongly promote cell elongation. GAs also promote the transition between vegetative and reproductive growth and are also required for pollen function during fertilization. Gibberellins breaks the dormancy (in active stage) in seeds and buds and helps increasing the height of the plant. It helps in the growth of the stem.
Sources: en.wikipedia.org
=== Amino acid basic structure === The general structure of the standard amino acids includes a primary amino group, a carboxyl group and the functional group attached to the α-carbon. The different amino acids are identified by the functional group. As a result of the three different groups attached to the α-carbon, amino acids are asymmetrical molecules. For all standard amino acids, except glycine, the α-carbon is a chiral center. In the case of glycine, the α-carbon has two hydrogen atoms, thus adding symmetry to this molecule. With the exception of proline, all of the amino acids found in life have the L-isoform conformation. Proline has a functional group on the α-carbon that forms a ring with the amino group.
=== Influence on the Democratic Party === Analysts have suggested that Sanders's campaign shifted both the Clinton campaign and the Democratic Party politically leftward. A new political organization, Brand New Congress, was formed in April 2016 by former campaign staffers. It works to elect congressional representatives with platforms in line with Sanders. In August 2016, he formed Our Revolution, a political organization dedicated to educating voters about issues, getting people involved in the political process, and electing progressive candidates for local, state, and national office. Speaking on the PBS Newshour about the upcoming 2018 elections and discussing the main principles of the two major parties, Susan Page described the Republican Party as "Trump's party" and the Democratic Party as "Bernie Sanders's party", saying that "Sanders and his more progressive stance has really taken hold." Noting the increasing acceptance of his national single-payer health-care program, his $15-an-hour minimum wage stance, free college tuition, and many of the other campaign platform issues he introduced, an April 2018 opinion article in The Week suggested, "Quietly but steadily, the Democratic Party is admitting that Sanders was right." In July 2016, a Slate article called the Democratic platform draft "a monument to his campaign", noting not only his call for a $15 minimum wage but other campaign issues, such as Social Security expansion, a carbon tax, Wall Street reform, opposition to the death penalty, and a "reasoned pathway for future legalization" of marijuana.
=== Tenure === In 2018, Dingell introduced a law that would give the Consumer Product Safety Commission the authority to recall defective firearms. John Dingell was a key lawmaker who initially granted the firearms industry this exemption from the 1972 Consumer Product Safety Act that created the Consumer Product Safety Commission. In July 2019, Dingell voted against a House resolution introduced by Representative Brad Schneider opposing efforts to boycott the State of Israel and the Global Boycott, Divestment, and Sanctions Movement. The resolution passed 398–17. In April 2021, Dingell introduced the Recovering America's Wildlife Act of 2021, a bill that would provide funding for conserving and protecting endangered and threatened species, strategies to do so, and wildlife-related recreational activities. The bill passed the House by 230–190 on June 14, 2022. In 2023, Dingell was among 56 Democrats to vote in favor of H.Con.Res. 21, which directed President Joe Biden to remove U.S. troops from Syria within 180 days.
Sources: en.wikipedia.org
We found ourselves rushing things, cutting things, making quality sacrifices we did not want to make." Montero said then they decided to re-evaluate the state of the project, set higher bars for the quality of work they wanted to produce, and started to back through what they had already done to improve upon that, at which point they were not sure when the project would be completed. The first standalone version of Black Mesa was released as a free download on September 14, 2012. This contained remakes of all Half-Life's chapters except the final chapter set on the alien world Xen, which the team intended to rework for inclusion in a future release, as Xen in the original Half-Life was often considered its weakest part. The development team estimated that the initial release of Black Mesa gave players eight to ten hours of content to complete. Black Mesa's initial release coincided with the launch of Valve's Steam Greenlight program which allowed users to vote for games to be put onto the Steam storefront. Black Mesa became one of the first ten titles to be voted on by fans and approved by Valve to be included on Steam through Greenlight.
It causes similar alterations on EEG readings and sleep architecture as benzodiazepines and causes disturbances in sleep architecture on withdrawal as part of its rebound effect. Zopiclone reduces both delta waves (slow-wave sleep) and the number of high-amplitude delta waves whilst increasing low-amplitude waves. Zopiclone reduces the total amount of time spent in REM sleep as well as delaying its onset. In EEG studies, zopiclone significantly increases the energy of the beta frequency band, increasing stage 2. Zopiclone is less selective to the α1 site and has higher affinity to the α2 site than zaleplon. Zopiclone is therefore very similar pharmacologically to benzodiazepines.
=== Availability === The "reference" version of BLOSUM is found in the NCBI toolkits. Both the older (deprecated) NCBI C Toolkit and the current NCBI C++ Toolkit provide the BLOSUM45, BLOSUM50, BLOSUM62, BLOSUM80, and BLOSUM90 matrices. Both also offer APIs for making use of the matrices. The original source code for calculating BLOSUM is also found on the NCBI website, at https://ftp.ncbi.nih.gov/repository/blocks/unix/blosum/. This archive "blosum.tar.Z" represents the original miscalculated version with improved search performance from 1992. The archive also contains pre-calculated BLOSUM outputs at the following similarity levels: "-2" (blosumn), 30, 40, 45, 50, 55, 60, 62, 65, 70, 75, 80, 85, 90, 95, and 100.
Sources: en.wikipedia.org
It indicates the oxidized form, which has a positive charge on the nicotinamide nitrogen. The reduced partner NADH lacks that charge and carries added electrons. The plus sign is part of the standard abbreviation, not a separate ion.
No. It also serves as a substrate for signaling and DNA-repair enzymes such as sirtuins and PARPs. Those reactions consume NAD+ and connect its availability to cellular regulation. Energy transfer remains its most abundant known role.
NAD+ is the oxidized electron acceptor, while NADH is the reduced electron carrier. They form a reversible redox pair and differ by a hydride ion. Cells maintain different ratios of the two depending on conditions and compartment.
The plus sign indicates the oxidized form of nicotinamide adenine dinucleotide, which can accept electrons. When it accepts electrons, it becomes NADH. The two forms together support redox reactions in cells.