This is a working overview of freeze-thaw, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-08-01 and is reviewed periodically as new material appears.
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 electron transfer, NAD+ serves as a substrate for enzymes that cleave it and attach its ADP-ribose portion to other molecules. This group includes poly(ADP-ribose) polymerases, CD38, and sirtuins. Such reactions consume NAD+ and can influence its availability for metabolism. Cells replenish NAD+ through a salvage pathway that recycles nicotinamide and through routes starting from tryptophan or vitamin B3 forms. How these synthesis and consumption routes are coordinated across tissues remains an active area of study, and compartment-specific concentrations are difficult to measure directly.
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.
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.
| 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. |
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.
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.
Solid NAD+ is relatively stable when kept dry, cold, and protected from light. Aqueous solutions are more vulnerable to hydrolysis and can lose activity during repeated freeze-thaw cycles or prolonged storage at ambient temperature. Stability depends on pH, ionic strength, and the presence of degrading enzymes or metal ions. For many laboratory uses, aliquots are stored frozen and thawed only once. Exact degradation rates vary by matrix, so stability should be checked for each application rather than assumed.
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.
NAD+ is relatively unstable in aqueous solution, especially at neutral or alkaline pH and at elevated temperatures. It is typically stored dry, protected from light and moisture, and kept cold or frozen for long-term use. Solutions are often prepared fresh or buffered to mildly acidic pH to slow hydrolysis. Repeated freeze-thaw cycles can reduce integrity. Laboratories may verify concentration using ultraviolet absorbance at 259 nm or by enzymatic assay. These handling practices are general laboratory conventions rather than universal rules.
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.
=== Anthropology and Race === In developing his psychological theories, Jung extensively studied the anthropological and ethnographic field work available to him at the time. This aspect of his work has become contentious and has spawned a significant body of scholarship. Some scholars argue that the anthropological theories that Jung relied on, as well as Jung's thinking itself, are implicated in colonial and racist conceptions of Indigenous and pre-modern cultures in which they were constructed as inferior to Europeans. Others have argued that such an approach oversimplifies both early anthropology as well as Jung's use of it, and that as a consequence Jung's anthropological thought retains relevance for contemporary evolutionary conceptions of the human mind. For example, Jung drew heavily on the ethnographic field work of Spencer and Gillen, who from 1896 to 1903 undertook extensive field work amongst the Arrernte people of Central Australia. While Spencer and Gillen's works were influenced by the surrounding prejudices of colonial culture, they also enabled the broader community to understand Indigenous culture and thereby help overcome those prejudices, understanding that continues to the present particularly in the relevance of their research to contemporary anthropology. Given the contemporary relevance of Spencer and Gillen's field work, particularly in relation to the Indigenous concept of the Dreaming, it has been argued that Jung's theories retain their relevance.
==== Spring ==== After a long period of consuming gimjang kimchi (김장김치) during the winter, fresh potherbs and vegetables were used to make kimchi. These kinds of kimchi were not fermented or even stored for long periods of time but were consumed fresh.
The Polish People's Republic (Polska Rzeczpospolita Ludowa) was established under the rule of the communist Polish United Workers' Party (PZPR). The name change from the Polish Republic was not officially adopted, however, until the proclamation of the Constitution of the Polish People's Republic in 1952. The ruling PZPR was formed by the forced amalgamation in December 1948 of the communist Polish Workers' Party (PPR) and the historically non-communist Polish Socialist Party (PPS). The PPR chief had been its wartime leader Władysław Gomułka, who in 1947 declared a "Polish road to socialism" as intended to curb, rather than eradicate, capitalist elements. In 1948 he was overruled, removed and imprisoned by Stalinist authorities. The PPS, re-established in 1944 by its left wing, had since been allied with the communists. The ruling communists, who in post-war Poland preferred to use the term "socialism" instead of "communism" to identify their ideological basis,[f] needed to include the socialist junior partner to broaden their appeal, claim greater legitimacy and eliminate competition on the political Left. The socialists, who were losing their organization, were subjected to political pressure, ideological cleansing and purges in order to become suitable for unification on the terms of the PPR. The leading pro-communist leaders of the socialists were the prime ministers Edward Osóbka-Morawski and Józef Cyrankiewicz. During the most oppressive phase of the Stalinist period (1948–1953), terror was justified in Poland as necessary to eliminate reactionary subversion.
Along with the international protection, Mexico has also sought similar protection for tequila in other important countries and regions through a number of bilateral and multilateral agreements. Pursuant to Annex 313 of the North American Free Trade Agreement (NAFTA), Canada and the United States recognize tequila and mezcal as products originating from Mexico and, consequently, do not permit the sale of any product as tequila and/or mezcal unless they have been lawfully prepared in Mexico. The Mexican government enforces the tequila intellectual property through the Mexican Institute of Industrial Property (IMPI). The use of the name tequila is authorized and administered only by IMPI. IMPI may prohibit any unauthorized use of the name that may create confusion for the consumers, or constitute an act of unfair competition. Despite protection under the Lisbon Agreement and NAFTA, tequila still faced competition from some pseudo tequilas. During the mid-1990s, as much as 3.5 million liters of these liquors were sold annually in Europe. The European liquors were produced from sugars of agave-like plants and were illegally labeled as tequila. Following the NAFTA precedent, Mexico entered into a bilateral agreement with the European Union concerning the mutual recognition and protection of AO in the spirits sector. Under this agreement the EU recognizes tequila and mezcal as "denominations of origin", although enforcement has still been quite lax in Europe.
=== Acquired === (G72.0 - G72.2) External substance induced myopathy (G72.0) Drug-induced myopathy Glucocorticoid myopathy is caused by this class of steroids increasing the breakdown of the muscle proteins leading to muscle atrophy. (G72.1) Alcoholic myopathy (G72.2) Myopathy due to other toxic agents, including atypical myopathy in horses caused by toxins in sycamore seeds and seedlings. (M33.0-M33.1) Dermatomyositis produces muscle weakness and skin changes. The skin rash is reddish and most commonly occurs on the face, especially around the eyes, and over the knuckles and elbows. Ragged nail folds with visible capillaries can be present. It can often be treated by drugs like corticosteroids or immunosuppressants. (M33.2) Polymyositis produces muscle weakness. It can often be treated by drugs like corticosteroids or immunosuppressants. Inclusion body myositis is a slowly progressive disease that produces weakness of hand grip and straightening of the knees. No effective treatment is known. (M60.9) Benign acute childhood myositis (M61) Myositis ossificans (M62.89) Rhabdomyolysis and (R82.1) myoglobinurias The Food and Drug Administration is recommending that physicians restrict prescribing high-dose simvastatin (Zocor, Merck) to patients, given an increased risk of muscle damage. The FDA drug safety communication stated that physicians should limit using the 80-mg dose unless the patient has already been taking the drug for 12 months and there is no evidence of myopathy.
Sources: en.wikipedia.org
To solve many of the above problems, as well as continuing the process of self-determination that was accompanying the dismantling of the Empire, it was proposed that Aden Colony should form a federation with the protectorates of East and West Aden. It was hoped that this would lessen Arab calls for complete independence, while still allowing British control of foreign affairs and the BP refinery at Little Aden to continue. It was the hope of the government of Harold Macmillan that creating a federation that would be dominated by the traditional sultans would allow for indirect British control as he wrote in his diary that his government planned to use "the Sultans to help us keep the colony and its essential defence facilities". However, the population of Aden was urban, well educated, secular and generally left-wing while the population of the protectorates were rural, mostly illiterate, religious and generally conservative, making the proposed federation a mismatch.
Ants have a cosmopolitan distribution. They are found on all continents except Antarctica, and only a few large islands, such as Greenland, Iceland, parts of Polynesia and the Hawaiian Islands lack native ant species. Ants occupy a wide range of ecological niches and exploit many different food resources as direct or indirect herbivores, predators and scavengers. Most ant species are omnivorous generalists, but a few are specialist feeders. There is considerable variation in ant abundance across habitats, peaking in the moist tropics to nearly six times that found in less suitable habitats. Their ecological dominance has been examined primarily using estimates of their biomass: myrmecologist E. O. Wilson had estimated in 2009 that at any one time the total number of ants was between one and ten quadrillion (short scale) (i.e., between 1015 and 1016) and using this estimate he had suggested that the total biomass of all the ants in the world was approximately equal to the total biomass of the entire human race. More careful estimates made in 2022 which take into account regional variations puts the global ant contribution at 12 megatons of dry carbon, which is about 20% of the total human contribution, but greater than that of the wild birds and mammals combined. This study also puts a conservative estimate of the ants at about 20 × 1015 (20 quadrillion). Ants range in size from 0.75 to 52 millimetres (0.030–2.0 in), the largest species being the fossil Titanomyrma giganteum, the queen of which was 6 cm (2+1⁄2 in) long with a wingspan of 15 cm (6 in).
Micelles consist of a hydrophobic inner core surrounded by a hydrophilic outer shell that is exposed to a solvent, and their structures can be spheres, disks or wormlike assemblies. Micelles form spontaneously when the concentration is above a critical micelle concentration and temperature. Amphiphiles with an intermediate level of hydrophobicity prefer to assemble into bilayer vesicles. Vesicles are spherical, hollow, lamellar structures that surround an aqueous core. The hydrophobic moiety faces inwards and forms the inner section of the bilayer, and the hydrophilic moiety is exposed to the aqueous environment on the inner and outer surface. Micelle structures have a hydrophobic interior and hydrophilic exterior. There is normally a distinct relationship between the amphiphilic character of a peptide and its function in that the amphiphilic character determines the self-assembly properties, and in turn this is what gives the peptide its functionality. The level of amphiphilicity can vary significantly in peptides and proteins; as such they can display regions that are either hydrophobic or hydrophilic in nature. An example of this is the cylindrical structure of an α-helix, as it could contain a section of hydrophobic residues along one face of the cylinder and a hydrophilic section of residues on the opposite face of the cylinder. For β-sheet structures, the peptide chain can be composed of alternating hydrophilic and hydrophobic residues, so that the side chains of the residues are displayed on opposite faces of the sheet.
== Structure == Mambalgins known to date consist of 57 amino acid residues and fold into a characteristic three-finger toxin (3FTx) structure. Two isoforms were originally described, called mambalgin-1 and mambalgin-2, which differ by a single amino acid residue. A third variant which differs by a single residue at another site, has subsequently been reported from venom profiling of the Eastern green mamba (Dendroaspis augusticeps). The X-ray structure of mambalgin-1 has been solved and consists of a three-finger protein fold with the typical three beta sheet-containing "finger" loops emanating from a central core stabilized by disulphide bonds; however, the structure differs from most 3FTx proteins in having an elongated second loop and shortened first and third loops. Mambalgins have relatively low sequence similarity to other 3FTx proteins and are most closely related to the 3FTx subclass known as the non-conventional or "weak" toxins. Human acid-sensing ion channel 1a inhibition (hASIC1aΔC) by snake toxin mambalgin1 develops a complex of three hASIC1aΔC subunits with six 6 NAG ligands (2 per subunit). The PDB code of this complex is 7CFT. Each hASIC1aΔC subunit is composed of an acid-sensing ion channel and a mambalgin1. Mambalgin1 is the toxin within hASIC1aΔC and is present in each subunit. The trimeric hASIC1aΔC shows a canonical chalice-like structure where each subunit of hASIC1aΔC harbors a cysteine-rich extracellular domain (ECD).
Sources: en.wikipedia.org
=== Exon-skipping === Antisense oligonucleotides (oligos), structural analogs of DNA, are the basis of a potential treatment for 10% of people with Duchenne muscular dystrophy. The compounds allow faulty parts of the dystrophin gene to be skipped when it is transcribed to RNA for protein production, permitting a still-truncated but more functional version of the protein to be produced. It is also known as nonsense suppression therapy. Two kinds of antisense oligos, 2'-O-methyl phosphorothioate oligos (such as drisapersen) and morpholino oligos (such as eteplirsen), have tentative evidence of benefit and are being studied. Eteplirsen is targeted to skip exon 51. "As an example, skipping exon 51 restores the reading frame of ~ 15% of all the boys with deletions. It has been suggested that by having 10 AONs to skip 10 different exons it would be possible to deal with more than 70% of all DMD boys with deletions." This represents about 1.5% of cases.
Similarly, in was Brasserie du Pêcheur v Germany the German government was liable to a French beer company for damages from prohibiting its imports, which did not comply with the fabled beer purity law. It was not decisive that the German Parliament had not acted willfully or negligently. It was merely necessary that there was (1) a rule intended to confer rights, (2) that a breach was sufficiently serious, and (3) there was a causal link between the breach and damage. The Court of Justice advised a breach is to be regarded as 'sufficiently serious' by weighing a range of factors, such as whether it was voluntary, or persistent. In Köbler v Republik Österreich the Court of Justice added that member state liability could also flow from judges failing to adequately implement the law. On the other hand, it is also clear that EU institutions, such as the commission, may be liable according to the same principles for failure to follow the law. The only institution whose decisions appear incapable of generating a damages claim is the Court of Justice itself.
The second presidency of Luiz Inácio Lula da Silva, also known as Lula's third government, began on 1 January 2023, when Luiz Inácio Lula da Silva returned to office for a third term as President of Brazil. A member of the Workers' Party (PT), Lula was elected in the second round of the 2022 presidential election, defeating incumbent president Jair Bolsonaro. He became the first Brazilian president to be elected to three terms and the first since Getúlio Vargas to return to the presidency after an interval between terms. The administration took office amid deep political polarization and the aftermath of the 2022–2023 Brazilian coup attempt, with the 8 January attacks on Brazil's government institutions constituting one of its first major political crises. The administration has been characterized by the restoration and expansion of social and public policies, changes to Brazil's fiscal and tax framework, and efforts to strengthen the role of the federal government. Major economic measures included the approval of a consumption tax reform and the replacement of the previous spending cap with a new fiscal framework. The government recorded periods of economic growth and declining unemployment, while facing concerns over public debt, fiscal sustainability, interest rates, household indebtedness, corporate financial difficulties, and the rising cost of living, particularly food prices.
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.
Aqueous NAD+ solutions are best kept frozen in aliquots and protected from light. Repeated freezing and thawing is avoided because it can accelerate breakdown. Dry powder stored desiccated at -20 °C or lower typically remains stable for longer periods.