salvage pathway is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2025-10-15. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical formula | C21H27N7O14P2 | Applies to the free acid form of beta-NAD+ |
| Molar mass | 663.43 g/mol | Calculated from the free acid formula |
| Redox couple | NAD+/NADH | Standard reduction potential near -0.32 V at pH 7 |
| Primary role | Electron carrier | Participates in oxidoreductase reactions |
| Common synonym | Diphosphopyridine nucleotide | Historical abbreviation DPN |
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.
Laboratory handling of NAD+ follows standard practices for hygroscopic fine chemicals. Personnel typically avoid inhalation and skin contact, use gloves and eye protection, and work in a ventilated area. Quality control may include ultraviolet absorbance at the nicotinamide maximum, chromatographic purity, water content, and identity confirmation by mass spectrometry. Because commercial preparations can contain counterions, residual solvents, or related nucleotides, a certificate of analysis helps verify the material. Researchers should confirm that the form supplied matches the intended assay.
Measuring NAD+ in biological samples requires care because the molecule is chemically reactive and present at low concentrations in some tissues. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and liquid chromatography coupled to mass spectrometry. Each method has different sensitivity and specificity, and sample preparation can affect results. Acidic or alkaline extraction steps are used in some protocols, but the choice depends on the analyte and matrix. No single method is universally optimal for every tissue or fluid.
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.
Beyond electron transfer, NAD+ serves as a substrate for enzymes that cleave the molecule and transfer ADP-ribose units. Sirtuins, poly(ADP-ribose) polymerases, and CD38 consume NAD+ in regulatory reactions. These activities link NAD+ availability to DNA repair, chromatin modification, calcium signaling, and metabolic stress responses. Because consumption can exceed biosynthesis under some conditions, cellular NAD+ levels are dynamic rather than fixed. Enzyme affinity and local synthesis also influence how much NAD+ is available for signaling.
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.
== Progress and status == The project has genetically engineered microorganisms to produce long-acting (glargine) and short-acting (lispro) insulin analogs using standard techniques in biotechnology and according to their December 2018 release the "first major milestone ― the production of insulin at lab scale ― is almost complete". The cost to produce insulin via Open Insulin methods is estimated by the project to be such that "roughly $10,000 should be enough to get a group started with the equipment needed to produce enough insulin for 10,000 people". A more recent estimate (May 2020) by the Open Insulin Foundation states that it will cost $200,000 (one-time price, per patient of $7-$20) for used equipment and up to $1,000,000 (one-time price, per patient of $73) for new equipment. The average price per vial was estimated to be $7 with each patient needing two vials per month.
Phenylacetic acid was added to switch it to producing the highly potent penicillin G. This strain could produce up to 550 milligrams of penicillin per litre. Pfizer was a small New York company that specialised in making citric acid, for which it had developed deep submergence techniques. This involved converting molasses to citric acid by fermenting it in a large tank in which it was stirred and the pH was carefully controlled. Pfizer's vice president, John L. Smith, whose daughter had died from an infection, put all of Pfizer's resources into the development of a practical deep submergence technique. The company invested $2.98 million in penicillin in 1943 and 1944 (equivalent to $55 million in 2025). Pfizer scientists Jasper H. Kane, G. M. Shull, E. M. Weber, A. C. Finlay and E. J. Ratajak worked on the fermentation process while R. Pasternak, W. J. Smith, V. Bogert and P. Regna developed extraction techniques.
Thus, the foundation of the food chain typically consists of primary producers. Primary producers, or autotrophs, utilize energy derived from either sunlight or inorganic chemical compounds to create complex organic compounds, such as starch, for energy. Because the sun's light is necessary for photosynthesis, most life could not exist if the sun disappeared. Even so, it has recently been discovered that there are some forms of life, chemotrophs, that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain in regions with little to no sunlight. Regardless of where the energy is obtained, a species that produces its own energy lies at the base of the food chain model, and is a critically important part of an ecosystem. Higher trophic levels cannot produce their own energy and so must consume producers or other life that itself consumes producers. In the higher trophic levels lies consumers (secondary consumers, tertiary consumers, etc.). Consumers are organisms that eat other organisms. All organisms in a food chain, except the first organism, are consumers. Secondary consumers eat and obtain energy from primary consumers, tertiary consumers eat and obtain energy from secondary consumers, etc.
=== Recycling === When galvanised steel is fed into an electric arc furnace, the steel is melted but the zinc coating is vaporised and becomes furnace dust; an average steel mill generates tens of thousands of tonnes of dust a year with a zinc content of 15–35%. Zinc can recovered from the dust by a number of processes, predominantly the Waelz process (90% in 2014). Recycling zinc produces 6.5 tonnes of CO₂ equivalent per tonne of zinc, compared with an average of 3.64 tonnes in the mining process. A number of experimental processes aim to increase efficiency, reduce overall energy expenditure, and lower CO₂ production to less than that generated by mining. These include the rotary hearth treatment of pelletised zinc containing dust (Kimitsu works, Nippon Steel); the SDHL (Saage, Dittrich, Hasche, Langbein) process, an efficiency modification of the Waelz process; the "DK process" a modified blast furnace process producing pig iron and zinc (oxide) dust from blast furnace dusts, sludges and other wastes; and the PRIMUS process (multi-stage zinc volatilisation furnace).
Sources: en.wikipedia.org
=== Role in cancer === Some of the laminin isoforms have been implicated in cancer pathophysiology. The majority of transcripts that harbor an internal ribosome entry site (IRES) are involved in cancer development via corresponding proteins. A crucial event in tumor progression, referred to as the epithelial-to-mesenchymal transition (EMT) allows carcinoma cells to acquire invasive properties. The translational activation of the extracellular matrix component laminin B1 (LAMB1) during EMT has been recently reported, suggesting an IRES-mediated mechanism. The IRES activity of LamB1 was determined by independent bicistronic reporter assays. Strong evidence excludes an impact of cryptic promoter or splice sites on IRES-driven translation of LamB1. Furthermore, no other LamB1 mRNA species arising from alternative transcription start sites or polyadenylation signals were detected that account for its translational control. Mapping of the LamB1 5'-untranslated region (UTR) revealed the minimal LamB1 IRES motif between -293 and -1 upstream of the start codon. RNA affinity purification demonstrated that the La protein interacts with the LamB1 IRES. This interaction and its regulation during EMT were confirmed by ribonucleoprotein immunoprecipitation. La is able to positively modulate LamB1 IRES translation, so LamB1 IRES is activated by binding to La which leads to translational upregulation during hepatocellular EMT.
In this series a panel of seven academics, journalists and historians named her among the group of people in the UK "whose actions during the reign of Elizabeth II have had a significant impact on lives in these islands and given the age its character". In 2015 Hodgkin's 1949 paper The X-ray Crystallographic Investigation of the Structure of Penicillin was honoured by a Citation for Chemical Breakthrough Award from the Division of History of Chemistry of the American Chemical Society presented to the University of Oxford (England). This research is notable for its groundbreaking use of X-ray crystallography to determine the structure of complex natural products, in this instance, of penicillin. Since 1999, the Oxford International Women's Festival has presented the annual Dorothy Hodgkin Memorial Lecture, usually in March, in honour of Hodgkin's work. The Lecture is a collaboration between Oxford AWiSE (Association for Women in Science & Engineering), Somerville College and the Oxford University Museum of Natural History.
=== Transorbital lobotomy === The Freeman-Watts prefrontal lobotomy still required drilling holes in the skull, so surgery had to be performed in an operating room by trained neurosurgeons. Walter Freeman believed this surgery would be unavailable to those he saw as needing it most: patients in state mental hospitals that had no operating rooms, surgeons, or anesthesia, and limited budgets. Freeman wanted to simplify the procedure so that psychiatrists could carry it out in psychiatric hospitals. Inspired by the work of Italian psychiatrist Amarro Fiamberti, Freeman at some point conceived of approaching the frontal lobes through the eye sockets instead of through drilled holes in the skull. In 1945, he took an ice pick from his own kitchen and began testing the idea on grapefruit and cadavers. The use of lobotomy in the United States was resisted and criticized heavily by American neurosurgeons. However, because Freeman managed to promote the success of the surgery through the media, lobotomy became touted as a miracle procedure, capturing the attention of the public and leading to an overwhelming demand for the operation. In 1945, Freeman streamlined the procedure, replacing it with transorbital lobotomy, in which a pick-like instrument was forced through the back of the eye sockets to pierce the thin bone that separates the eye sockets from the frontal lobes. The pick's point was then inserted into the frontal lobe and used to sever connections in the brain (presumably between the prefrontal cortex and thalamus).
Throughout the times, there have been a variety of architectural styles, from those of indigenous peoples to contemporary ones, passing through colonial (military and religious), Republican, transition and modern styles.
Reiko Nagatsuki (長月 礼子, Nagatsuki Reiko) Voiced by: Misato Matsuoka Member of the Agency Autumn Division's Security Department. She is responsible for the Town of Autumn's security system. She is an intelligent woman with a career that allows her to operate flexibly. She considers Rindo a little brother. Ishihara (石原, Ishihara) Voiced by: Haruna Mikawa (Japanese); Cassie Ewulu (English) An employee of the Agency of the Four Seasons' Security Department. She is assigned to the Agent of Winter's security and also serves as Rousei's psychologist. She is a calm woman with excellent qualities in her duties.
Sources: en.wikipedia.org
If Carcass wasn't killed and Simon didn't give the gun to the doctor, he kills Sophie, his therapist, and then himself. He leaves a suicide note stating that he would have killed more people if it weren't for his disability and wishes that the people who find his body are haunted by it for the rest of their life. If Carcass wasn't killed and Simon gave the gun to the doctor, he kills Sophie, then himself. In his suicide note, he apologizes to his therapist and thanks him for his help, explaining that he killed Sophie so that he could have her all to himself since he never got over her rejection. If Carcass was killed and Simon didn't give the gun to the doctor, he kills his doctor, then himself. In his suicide note, he states that the doctor's therapy only made things worse, and begs for Sophie not to know what he's done. If Carcass was killed and Simon gave the gun to the doctor, Simon, right before he kills himself, is confronted by Book Simon. The player, taking control of the real Simon, chases down and kills Book Simon in a shootout. Coming to his senses, Simon realizes he had a mental episode. Instead of taking his own life, he killed two police officers who were presumably checking in on him. Simon gets admitted into a mental hospital for the rest of his life, where his therapist continues to look after him. Sophie, despite how much Simon hurt her, visits him. Hopeful about the future and finally at peace with his demons, Simon finishes his book.
Widespread travel by naturalists in the early-to-mid-19th century resulted in a wealth of new information about the diversity and distribution of living organisms. Of particular importance was the work of Alexander von Humboldt, which analyzed the relationship between organisms and their environment (i.e., the domain of natural history) using the quantitative approaches of natural philosophy (i.e., physics and chemistry). Humboldt's work laid the foundations of biogeography and inspired several generations of scientists.
It was the country's only NGO specializing in media issues, Internet access, and media monitoring during election campaigns. It had operated without government approval, and had monitored violations of journalists' rights and had taken up the cause of the ban on the dissemination of many newspapers and magazines. Ba'athist Syrian security forces arrested and beat up protestors on 15 June 2020. The protest started on 7 June 2020, in front of the governorate center against government's failure of handling economic downfall, deteriorating living conditions and corruption. HRW appealed the Syrian authority to release the peacefully protesting detainees. Pro-regime journalists who were allowed to report within the country were arrested by security forces over social media posts or ambiguous charges like being "out of line".
=== TIME framework and Triangle of Wound Assessment (TWA) === To assist clinicians in standardizing the wound assessment and preparation of wound bed for treatment, the TIME framework was developed in 2002 by a group of wound care experts. The TIME acronym stands for Tissue, Infection/Inflammation, Moisture, and Edge – components that, per the TIME recommendation, should be thoroughly assessed to optimize the treatment. Depending on the clinical findings for each component, TIME recommends certain clinical actions aimed at correcting the issues and facilitating healing. A recent global anthropological study has prompted clinicians to review the TIME framework and resulted in a 2016 development of a comprehensive tool for wound assessment – the Triangle of Wound Assessment (TWA). Based on the study's findings, TWA identifies three zones (wound bed, wound edge, and periwound skin) that must be included in wound assessment to arrive at clinical decisions that will help heal the wound in the most efficient way. TIME framework components are integrated into the assessment of each zone. The introduction of periwound skin as a component of wound assessment identifies a significant departure from traditional methods; it emphasizes the importance of addressing periwound skin during treatment in the same measure as wound bed and wound edge. Wound assessment is a holistic process that considers the patient's current state of health, the factors that may impede wound healing, and the cause, duration and state of the wound. As such, this process is applicable to any wound.
Enterotoxins are potent compounds produced by various microorganisms that specifically target and damage the intestines, causing many of the most rapid and severe forms of food poisoning. Unlike bacterial infections that require live organisms to multiply in the gut, enterotoxins (a type of exotoxin) can cause illness even when the bacteria that produced them have been killed through cooking or other preservation methods. Symptom onset varies with the toxin but may be rapid in onset, as in the case of enterotoxins of Staphylococcus aureus in which symptoms appear in one to six hours. This causes intense vomiting including or not including diarrhea (resulting in staphylococcal enteritis), and staphylococcal enterotoxins (most commonly staphylococcal enterotoxin A but also including staphylococcal enterotoxin B) are the most commonly reported enterotoxins although cases of poisoning are likely underestimated. It occurs mainly in cooked and processed foods due to competition with other biota in raw foods, and humans are the main cause of contamination as a substantial percentage of humans are persistent carriers of S. aureus. The CDC has estimated about 240,000 cases per year in the United States.
Sources: en.wikipedia.org
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.
No; NAD+ and related dinucleotides occur across bacteria, archaea, plants, fungi, and animals. Its central role in electron transfer and enzyme catalysis is deeply conserved, though specific pathways for making and using it can differ among organisms.
NAD+ is a charged, water-soluble dinucleotide and generally does not diffuse freely across cell membranes. Cells rely on precursor molecules and dedicated transport or salvage pathways. This limited permeability shapes how researchers deliver or measure NAD+ in experimental systems.
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.