This is a working overview of Sirtuin substrate, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-11-18 and is reviewed periodically as new material appears.
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.
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.
Nicotinamide adenine dinucleotide, abbreviated NAD+, is a dinucleotide composed of two nucleotides joined by phosphate groups. One nucleotide contains adenine; the other contains nicotinamide. The molecule exists in oxidized (NAD+) and reduced (NADH) forms, and the reversible hydride transfer between them underlies many metabolic oxidation-reduction reactions. In cells, NAD+ serves as an electron acceptor in pathways such as glycolysis, the citric acid cycle, and oxidative phosphorylation. Its concentration and redox ratio vary by compartment, tissue, and metabolic state.
| 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. |
Solid NAD+ is usually supplied as a white to off-white powder or lyophilized preparation. It is hygroscopic and should be kept desiccated at low temperature, commonly -20 °C or below for long-term storage. Aqueous solutions are less stable than dry material and are often prepared fresh or stored frozen in aliquots. Light exposure and repeated freeze-thaw cycles can promote degradation, so amber containers and single-use aliquots are preferred. Buffered solutions near neutral pH are generally less stable than acidic or frozen preparations.
Quantification of NAD+ in biological samples typically uses liquid chromatography coupled to mass spectrometry. Enzymatic cycling assays offer higher throughput and rely on NAD+ dependent dehydrogenases to amplify signal. Both approaches require careful sample quenching because NAD+ can be rapidly consumed or converted after collection. Acidic extraction is common for NAD+, while alkaline conditions favor NADH in some protocols. Isotopically labeled internal standards help correct for losses during extraction and ionization.
Commercial NAD+ is available at research grade, often with purity specifications determined by high-performance liquid chromatography. Certificates of analysis may report water content, residual solvents, and counterion identity. Identity can be confirmed by ultraviolet absorbance near 260 nm, mass spectrometry, or enzymatic activity. Because different salt forms and hydration states exist, researchers should verify that the product matches the intended molecular form. Lot-to-lot variation in purity can affect quantitative assays and should be documented.
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.
Biosynthesis of NAD+ starts from nicotinamide, nicotinic acid, or nicotinamide riboside through salvage pathways. A rate-limiting enzyme, nicotinamide phosphoribosyltransferase, converts nicotinamide to nicotinamide mononucleotide. Further coupling with ATP yields NAD+. In mammals, the liver and muscle can synthesize NAD+ from dietary precursors, but tissue levels vary widely. Researchers study these pathways to understand age-related changes, metabolic disorders, and neurodegeneration. Direct causal links between NAD+ decline and disease remain an active area of investigation.
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.
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.
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.
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.
=== Complications === Compartment syndrome is a clinical diagnosis, i.e., no diagnostic test conclusively proves its presence or absence, but direct measurement of the pressure in a fascial compartment, and the difference between this pressure and the blood pressure, may be used to assess its severity. High pressures in the compartment and a small difference between compartment pressure and blood pressure indicate that the blood supply is likely to be insufficient, and that surgical intervention may be needed. Disseminated intravascular coagulation, another complication of rhabdomyolysis and other forms of critical illness, may be suspected based on unexpected bleeding or abnormalities in hematological tests, such as a decreasing platelet count or prolongation of the prothrombin time. The diagnosis can be confirmed with standard blood tests for DIC, such as D-dimer.
However, we insisted on: national character of Charter, freedom of immigration and internal autonomy, and at the same time full rights of citizenship to [illegible] and Jews in Palestine." In Sykes's mind, the agreement which bore his name was outdated even before it was signed – in March 1916, he wrote in a private letter: "to my mind the Zionists are now the key of the situation". In the event, neither the French nor the Russians were enthusiastic about the proposed formulation and eventually on 4 July, Wolf was informed that "the present moment is inopportune for making any announcement." These wartime initiatives, inclusive of the declaration, are frequently considered together by historians because of the potential, real or imagined, for incompatibility between them, particularly in regard to the disposition of Palestine. In the words of Professor Albert Hourani, founder of the Middle East Centre at St Antony's College, Oxford: "The argument about the interpretation of these agreements is one which is impossible to end, because they were intended to bear more than one interpretation."
Cystathionine is an intermediate in the synthesis of cysteine from homocysteine. It is produced by the transsulfuration pathway and is converted into cysteine by cystathionine gamma-lyase (CTH). Biosynthetically, cystathionine is generated from homocysteine and serine by cystathionine beta synthase (upper reaction in the diagram below). It is then cleaved into cysteine and α-ketobutyrate by cystathionine gamma-lyase (lower reaction). An excess of cystathionine in the urine is called cystathioninuria.
Mature HIV protease exists as a 22 kDa homodimer, with each subunit made up of 99 amino acids. A single active site lies between the identical subunits and has the characteristic Asp-Thr-Gly (Asp25, Thr26 and Gly27) catalytic triad sequence common to aspartic proteases. As HIV-1 PR can only function as a dimer, the mature protease contains two Asp25 amino acids, one from each monomer, that act in conjunction with each other as the catalytic residues. Additionally, HIV protease has two molecular "flaps" which move a distance of up to 7 Å when the enzyme becomes associated with a substrate. This can be visualized with animations of the flaps opening and closing.
Sources: en.wikipedia.org
=== Portuguese === Luso-American Financial - A Fraternal Benefit Society - Founded in 1868 as the Portuguese Protective and Benevolent Association of the City and County of San Francisco. Grand Council, most likely a state organization, was founded in 1872, and Supreme Council in 1921. Changed name to Benevolent Society of California in 1948. Women were admitted in 1945. Merged with the Uniao Portuguesa Continental do Estado da California (f.1917) in 1957 to become United National Life Insurance Society, later adopted its current name. Reincorporated in 1975. Luso-American Fraternal Federation founded in 1957 to administer fraternal aspect. Administers Luso-American Educational Foundation which grants scholarships to students interested in Portuguese history and culture. Headquarters in Oakland, lodges called "Subordinate lodges" which were present in California, Nevada, Massachusetts, Connecticut, and Rhode Island. In 1978 it had 14,000 members. In 1994 it was reported to have 15,000. Membership is open to Americans of Portuguese descent or birth. Society of the Holy Spirit of the State of California - Founded in Santa Clara, California, in 1895. Headquartered in Santa Clara. Lodges are called Subordinate Councils; the highest is known as the "Supreme Council" which holds a convention annually. Membership is open to all. 1979 membership 11,500, a slight increase since 1972. There is a ritual with provisions for questions and answers, hymns pledges, and passwords.
=== External nasal anatomy === The form of the nasal subunits—the dorsum, the sidewalls, the lobule, the soft triangles, the alae, and the columella—are configured differently, according to the race and the ethnic group of the patient, thus the nasal physiognomies denominated as: African, platyrrhine (flat, wide nose); Asiatic, subplatyrrhine (low, wide nose); Caucasian, leptorrhine (narrow nose); and Hispanic, paraleptorrhine (narrow-sided nose). The respective external nasal valve of each nose is variably dependent upon the size, shape, and strength of the lower lateral cartilage.
A traditional application of methylene blue is the intravital or supravital staining of nerve fibers, an effect first described by Paul Ehrlich in 1887. A dilute solution of the dye is either injected into tissue or applied to small freshly removed pieces. The selective blue coloration develops with exposure to air (oxygen) and can be fixed by immersion of the stained specimen in an aqueous solution of ammonium molybdate. Vital methylene blue was formerly much used for examining the innervation of muscle, skin, and internal organs. The mechanism of selective dye uptake is incompletely understood; vital staining of nerve fibers in skin is prevented by ouabain, a drug that inhibits the Na/K-ATPase of cell membranes.
Sources: en.wikipedia.org
These volumes were held in the Senate wing of the Capitol; one surviving volume was a government account book from 1810. The volume was taken by British Admiral George Cockburn as a souvenir, and was later returned to the U.S. in 1940 by his family. Within a month, Jefferson offered to sell his large personal library as a replacement. He had reconstituted his own collection after losing part of it to a fire. Congress accepted the offer in January 1815, appropriating $23,950 to purchase his 6,487 books. Some House members, including New Hampshire representative Daniel Webster, opposed the purchase, wanting to exclude "books of an atheistical, irreligious, and immoral tendency". Jefferson's collection, gathered over 50 years, covered various subjects and languages, including topics not typically found in a legislative library. He believed all subjects had a place in the Library of Congress, stating:
Psychiatric care may be required following recovery. A liver transplant may be required if damage to the liver becomes severe. The need for transplant is often based on low blood pH, high blood lactate, poor blood clotting, or significant hepatic encephalopathy. With early treatment, liver failure is rare. Death occurs in about 0.1% of cases. Paracetamol poisoning was first described in the 1960s. Rates of poisoning vary significantly between regions of the world. In the United States more than 100,000 cases occur a year. In the United Kingdom it is the medication responsible for the greatest number of overdoses. Young children are most commonly affected. In the United States and the United Kingdom, paracetamol is the most common cause of acute liver failure.
UK-447841 is a neprilysin inhibitor (NEPI) which was under development for the treatment of female sexual dysfunction. It is taken as-needed orally. The drug is intended to work by inhibiting vasoactive intestinal peptide (VIP) hydrolysis by neprilysin (NEP). However, neprilysin is also involved in the metabolism of more than 50 other hormones and neuropeptides, for instance oxytocin among others. UK-447841 was under development by Pfizer. It reached phase 2 clinical trials prior to the discontinuation of its development in 2008.
== Sponsored events == Chick-fil-A Classic The Chick-fil-A Classic is a high school basketball tournament held in Columbia, South Carolina, featuring nationally ranked players and teams. The tournament is co-sponsored by the Greater Columbia Educational Advancement Foundation (GCEAF), which provides scholarships to high school seniors in the greater Columbia area. Chick-fil-A Peach Bowl The Chick-fil-A Peach Bowl, first known as the Peach Bowl until 2006 and renamed Chick-fil-A Peach Bowl in 2014, is a college football bowl game played each year in Atlanta, Georgia. Chick-fil-A Kickoff Game The Chick-fil-A Kickoff Game is an annual early-season college football game played at the Mercedes-Benz Stadium in Atlanta, Georgia; before 2017, it was played at the Georgia Dome. It features two highly ranked teams, one of which has always been from the Southeastern Conference. The event was expanded to two games in the 2012 season and again in the 2014 season. It was also two games in 2017. On July 12, 2023, Georgia-based insurance company Aflac, became the new sponsor of the game.
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.
NAD+ is a coenzyme found in all living cells. It carries electrons in metabolic reactions and also serves as a substrate for enzymes involved in signaling and DNA repair. Its oxidized and reduced forms are central to energy metabolism.