A practical reference on mass spectrometry: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-08-01. Anything still debated is marked as such rather than presented as settled.
Enzymatic stability motivates the extra three residues at the carboxyl end. Native tuftsin is cleaved quickly by circulating aminopeptidases and carboxypeptidases, which limits its duration of action and its usefulness as a tool compound. Extending the chain with proline-rich segments is a common design tactic because proline constrains the backbone and slows proteolysis. The same Pro-Gly-Pro motif appears in other Russian-developed peptides of the era. Whether the full seven-residue chain is required for activity, or whether it acts mainly as a prodrug releasing tuftsin, remains unresolved.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its four N-terminal residues reproduce tuftsin, a tetrapeptide fragment of the immunoglobulin heavy chain, while the C-terminal Pro-Gly-Pro extension is a synthetic addition. The peptide has a molecular mass near 752 daltons and carries a net positive charge at physiological pH because of the arginine and lysine side chains. Published indexes list it under the name Selank and the sequence abbreviation TKPRPGP. Solid-phase peptide synthesis is the standard production route for research quantities.
Development took place at the Institute of Molecular Genetics of the Russian Academy of Sciences, where a series of short peptides were designed in the 1980s and 1990s. Selank was selected from variants of tuftsin that showed resistance to plasma peptidases. Russian regulatory approval covers it as an anxiolytic agent given intranasally. Outside that market the compound is normally handled as a research chemical rather than a medicine, and no widely recognised international pharmacopoeial monograph exists. The name Selank is a coined trade designation rather than a systematic chemical name.
Solubility behavior is a practical concern for handling. Selank dissolves readily in water and in common aqueous buffers, which simplifies preparation of working solutions. The choice of solvent, ionic strength, and pH can influence aggregation over time, particularly at higher concentrations. Aqueous solutions are typically sterile-filtered before use. Because stability depends on several variables, storage and handling notes should be treated as general guidance rather than fixed rules, and specific values are best confirmed against a certificate of analysis for each batch.
Characterization of Selank in a laboratory setting relies on standard peptide methods. Reverse-phase high-performance liquid chromatography separates the target from related impurities and provides a purity figure, commonly reported as 95 percent or higher. Mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, confirms the molecular mass and helps detect truncation or modification. Amino acid analysis can verify composition when a sequence-level check is needed. These techniques together establish identity and purity for a given lot.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Tuftsin analogue with a C-terminal Pro-Gly-Pro tail |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Abbreviated TKPRPGP in most catalogues |
| Molecular mass | About 752 Da | Value for the free peptide |
| Solubility | Freely soluble in water | Aqueous solutions are kept cold and used promptly |
| Typical storage | -20 °C, dry, protected from light | Applies to the lyophilised powder before reconstitution |
Peptide bonds in selank are susceptible to hydrolysis under strongly acidic or basic conditions, and the terminal proline residues are vulnerable to exopeptidase activity in biological samples. Lyophilized powder stored dry at -20 °C typically remains stable for extended periods, whereas aqueous solutions degrade faster and may lose measurable purity within days to weeks depending on pH, temperature, and microbial load. Repeated freeze-thaw cycles promote aggregation and adsorption to container surfaces. For analytical work, solutions are usually prepared fresh, kept cold, and used within a single working day.
Handling follows standard practice for research peptides. Material is weighed in a low-humidity environment because the powder absorbs atmospheric moisture. Purity is reported as the percentage area of the main peak in a chromatogram, with specifications commonly set at 95 percent or higher; values below that threshold indicate the presence of truncated or modified species. Residual trifluoroacetate from purification is often present and may affect mass balance. Certificates of analysis should state the analytical method, the column and gradient used, and the lot-specific retention time so that results can be compared across suppliers.
Identity and purity of selank are established with reversed-phase high-performance liquid chromatography coupled to mass spectrometry. The peptide elutes from C18 columns with acetonitrile gradients in water containing trifluoroacetic acid or formic acid, and detection is usually performed by ultraviolet absorbance near 214 nm. Electrospray ionization in positive mode gives a doubly protonated ion near m/z 377, consistent with a mass of about 752 Da. Amino acid analysis or tandem mass spectrometry of fragment ions confirms the sequence. Because the molecule has no aromatic residues, it lacks a usable 280 nm chromophore, so low-wavelength detection or mass spectrometry is required.
Measuring peptide exposure inside the brain is technically difficult. Selank is degraded rapidly in plasma, and assays must separate intact peptide from fragments, which favors targeted mass spectrometry over immunoassays alone. Reported half-lives are short, on the order of minutes, so effects observed hours later are attributed to downstream signaling rather than to the parent compound. Blood-brain barrier permeability is debated and rarely quantified directly. Gaps include absent dose-response characterization, inconsistent reporting of purity, and almost no pharmacokinetic data from human participants.
Selank is studied chiefly as an animal-model anxiolytic with proposed secondary effects on memory and immune signaling. Reported mechanisms include modulation of the GABA-A receptor complex, inhibition of enkephalin-degrading enzymes, and shifts in monoamine turnover within limbic structures. Some experiments describe increased expression of brain-derived neurotrophic factor in the hippocampus after repeated dosing. No single molecular target has been confirmed, and the peptide does not bind any receptor with the selectivity typical of a conventional small-molecule drug. Mechanism therefore remains a set of hypotheses rather than an established pathway.
Various reform strategies were proposed for healthcare, and in March 2010, the Patient Protection and Affordable Care Act was enacted as a means of health care reform. CBO reduced its per capita Medicare spending assumptions by $1,000 for 2014 and $2,300 for 2019, relative to its 2010 estimate for those years. If this trend continues, it will significantly improve the long-term budget outlook. Social Security is a social insurance program officially called "Old-Age, Survivors, and Disability Insurance" (OASDI), in reference to its three components. It is primarily funded through a dedicated payroll tax of 12.4%. During 2016, total benefits of $910 billion were paid out, versus $882 billion in 2015, an increase of $28 billion or 3%. Social Security's total expenditures have exceeded its non-interest income since 2010. The deficit of non-interest income relative to cost was about $49 billion in 2010, $45 billion in 2011, and $55 billion in 2012. During 2010, an estimated 157 million people paid into the program and 54 million received benefits, roughly 2.91 workers per beneficiary. Since the Greenspan Commission in the early 1980s, Social Security has cumulatively collected far more in payroll taxes dedicated to the program than it has paid out to recipients—nearly $2.6 trillion in 2010. This annual surplus is credited to Social Security trust funds that hold special non-marketable Treasury securities. This surplus amount is commonly referred to as the "Social Security Trust Fund." The proceeds are paid into the U.S.
== J == Sophie E. Jackson (active from 1991). Biochemist at the University of Cambridge known for work on protein folding. Alec Jeffreys FRS (b. 1950). British biochemist and geneticist at Leicester University, known for inventing genetic fingerprinting. William Jencks FRS (foreign member) (1927–2007). American biochemist at Brandeis University, known for applying chemical mechanisms to enzyme-catalysed reactions and for his masterly book Catalysis in Chemistry and Enzymology. Member Natl. Acad. Sci. USA. Thomas H. Jukes (1906–1999). British-American biologist at UC Berkeley known for work in nutrition and molecular evolution. He was very active in denouncing pseudoscience. John Michael Jumper (b. 1985). American chemist and computer scientist at DeepMind Technologies. Nobel Prize in chemistry, 2024.
==== Usage of Protein Nanoprobes to Study Protein-Protein Interactions with Mass Spectrometry ==== Protein was studied using a protein nanoprobe (that enables cross-linking) that introduced photo-methionine within the protein (during the recombinant expression) which lead to the protein keeping its reserved structure while having the ability to be mapped out for its interactions. The model was used as a region of contact surface that is involved in a well-known interaction (homodimerization) between two molecules of 14-3-3ζ protein. Once the photo-methionine is introduced and has become activated using UV-light, it can cross-link with no specificity (meaning no group) and the links have zero-length. High resolution mass spectrometry or MS can (even MS/MS) be used then to determine the cross-linked residues and the reaction radius; allowing the researchers to characterize and research the homodimerization of the protein. The usage of the high-resolution MS with photo-methionine has its advantages as it again allows the protein to be in its native state, there are reasonable time scales while using small quantities of the protein. There are also fewer limitations on the reaction specificity and restrictions using a photo-active cross-linker (photo-methionine) compared to chemical cross-linking. This method of combined photo-initiated cross-linking from the protein nanoprobe in tandem with MS could be useful to characterize not only homodimer formation but also oligomers and in theory; heteromers (such as the composition of the protein-protein mixture and its functionality).
The GoldSrc engine did not provide as much precise control for the player during jumping, making these jumps difficult and often with Freeman falling into a void and the player restarting the game. Wired's Julie Muncy called the Xen sequence "an abbreviated, unpleasant stop on an alien world with bad platforming and a boss fight against what appeared, by all accounts, to be a giant floating infant". The Electric Playground said that Half-Life was an "immersive and engaging entertainment experience" in its first half and that it "peaked too soon". During the AIAS' 2nd Annual Interactive Achievement Awards, Half-Life was awarded "Computer Entertainment Title of the Year" and "PC Action Game of the Year"; it also received nominations for "Game of the Year" and outstanding achievement in "Art/Graphics", "Character or Story Development", "Interactive Design", and "Software Engineering". Jeff Lundrigan reviewed the PlayStation 2 version for Next Generation, rating it three out of five, and wrote that "it may be getting old, but there's still a surprising amount of life in Half-Life". The PlayStation 2 version was a nominee for The Electric Playground's 2001 Blister Awards for "Best Console Shooter Game", but lost to Halo: Combat Evolved for Xbox. In 1999, 2001, and 2005, PC Gamer named Half-Life the best PC game of all time. In 2004, GameSpy readers voted Half-Life the best game of all time. Gamasutra gave it their Quantum Leap Award in the FPS category in 2006. GameSpot inducted Half-Life into their Greatest Games of All Time list in May 2007.
The enteric nervous system consists of some one hundred million neurons that are embedded in the peritoneum, the lining of the gastrointestinal tract extending from the esophagus to the anus. These neurons are collected into two plexuses – the myenteric (or Auerbach's) plexus that lies between the longitudinal and the smooth muscle layers, and the submucosal (or Meissner's) plexus that lies between the circular smooth muscle layer and the mucosa. Parasympathetic innervation to the ascending colon is supplied by the vagus nerve. Sympathetic innervation is supplied by the splanchnic nerves that join the celiac ganglia. Most of the digestive tract is innervated by the two large celiac ganglia, with the upper part of each ganglion joined by the greater splanchnic nerve and the lower parts joined by the lesser splanchnic nerve. It is from these ganglia that many of the gastric plexuses arise.
Sources: en.wikipedia.org
Recognizing and evaluating hyperthyroidism in pregnancy is a diagnostic challenge. Thyroid hormones are commonly elevated during the first trimester of pregnancy as the pregnancy hormone human chorionic gonadotropin (hCG) stimulates thyroid hormone production, in a condition known as gestational transient thyrotoxicosis. Gestational transient thyrotoxicosis generally abates in the second trimester as hCG levels decline and thyroid function normalizes. Hyperthyroidism can increase the risk of complications for mother and child. Such risks include pregnancy-related hypertension, pregnancy loss, low-birth weight, pre-eclampsia, preterm delivery, still birth and behavioral disorders later in the child's life. Nonetheless, high maternal FT4 levels during pregnancy have been associated with impaired brain developmental outcomes of the offspring and this was independent of hCG levels. Propylthiouracil is the preferred antithyroid medication in the 1st trimester of pregnancy as it is less teratogenic than methimazole.
In animal and Human biology, a tendon cell is a cell that makes up tendons, the bands of connective tissue that connects muscles to bones. Tendon cells, also known as tenocytes or tendon fibroblasts, are specialized cells that contribute to the structure, function, and repair of tendons in the body. Tendons are fibrous tissues that connect muscles to bones, and tendon cells play a vital role in maintaining tendon homeostasis and facilitating healing following injury.
== Use == The first publication on vinylene carbonate described its Diels-Alder reaction using the example of its addition reaction with 2,3-dimethylbutadiene to a bicyclic carbonate and subsequent hydrolysis to cis-4,5-dihydroxy-1,2-cyclohexene:
Unnatural amino acids incorporated into proteins include heavy atom-containing amino acids to facilitate certain x-ray crystallographic studies; amino acids with novel steric/packing and electronic properties; photocrosslinking amino acids which can be used to probe protein-protein interactions in vitro or in vivo; keto, acetylene, azide, and boronate-containing amino acids which can be used to selectively introduce a large number of biophysical probes, tags, and novel chemical functional groups into proteins in vitro or in vivo; redox active amino acids to probe and modulate electron transfer; photocaged and photoisomerizable amino acids to photoregulate biological processes; metal binding amino acids for catalysis and metal ion sensing; amino acids that contain fluorescent or infra-red active side chains to probe protein structure and dynamics; α-hydroxy acids and D-amino acids as probes of backbone conformation and hydrogen bonding interactions; and sulfated amino acids and mimetics of phosphorylated amino acids as probes of post-translational modifications. Availability of the non-standard amino acid requires that the organism either import it from the medium or biosynthesize it. In the first case, the unnatural amino acid is first synthesized chemically in its optically pure L-form. It is then added to the growth medium of the cell. A library of compounds is usually tested for use in incorporation of the new amino acid, but this is not always necessary, for example, various transport systems can handle unnatural amino acids with apolar side-chains.
Sources: en.wikipedia.org
Selank is a seven-amino-acid peptide built from the tuftsin sequence plus a Pro-Gly-Pro tail. It is produced by chemical synthesis rather than extracted from a natural source. The free peptide is usually supplied as a lyophilised powder or in an aqueous formulation.
Tuftsin is a natural tetrapeptide derived from the Fc portion of immunoglobulin G. Selank retains that tetrapeptide at its N-terminus and adds three residues to improve resistance to enzymatic breakdown. The relationship is structural, and the two molecules are not interchangeable in experimental work.
It holds a product registration in Russia for intranasal use as an anxiolytic. Registrations of that kind are not automatically accepted by regulators elsewhere. In most other countries it is treated as an unapproved substance or a research material.
Reverse-phase HPLC is the usual method and gives a percentage purity value. Mass spectrometry then confirms the molecular mass. Together they provide a basic identity and purity profile for a lot.