This is a working overview of Enkephalinase, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-07-23. Anything still debated is marked as such rather than presented as settled.
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
Proposed mechanisms centre on modulation of the GABAergic system, with reports of altered expression of genes related to GABA-A receptor subunits and changed monoamine turnover. Some studies describe inhibition of enkephalinase, the enzyme that degrades endogenous enkephalins, which may prolong opioid peptide signalling. Effects on brain-derived neurotrophic factor and on cytokine expression have also been reported. These findings come largely from animal models and small human studies, and the precise primary target remains unresolved.
Lyophilized Selank, the dry powder form, is generally stored frozen at minus 20 degrees Celsius or colder for long-term keeping. The solid is hygroscopic and should stay sealed, dry, and protected from light. Once dissolved, the peptide is less stable and is usually held refrigerated at 2 to 8 degrees Celsius for short periods. Repeated freezing and thawing is avoided because it can promote aggregation and loss of activity. Buffers and pH choice also affect how long a solution remains usable.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C33H57N11O9 | Free peptide form |
| Molecular mass | About 751.9 Da | Calculated average mass |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Single-letter form TKPRPGP |
| Structural basis | Tuftsin analogue | Extended version of a natural tetrapeptide |
| Development origin | Russian Academy of Sciences | Work carried out from the 1980s onward |
Published work on this peptide almost always uses intranasal delivery, with drops or a spray applied to the nasal mucosa. Some animal experiments have used subcutaneous or intraperitoneal injection, and a smaller number have compared routes directly. Oral administration is not a focus of the literature, because short peptides of this size are broken down by digestive enzymes and cross intestinal barriers poorly. How much of an intranasal dose reaches the bloodstream intact in humans remains an open question.
Animal studies have examined behaviour in tests of anxiety, memory retention and stress response, and several report changes in neurotrophic or neurotransmitter-related markers. The human evidence base is much smaller, consisting mainly of short trials conducted in Russia with limited reporting in English-language journals. Sample sizes are modest and outcome measures vary between studies, so the findings are best described as preliminary. Independent replication under modern trial standards has not been widely reported.
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.
The Mark V initially used a single power source for the flashlight, sprinting, and oxygen supply; in Half-Life 2: Episode Two the flashlight was given a separate power source to improve gameplay. The symbol on Gordon's HEV suit is the lowercase Greek letter Lambda, λ. This symbol is used by scientists to denote the decay constant of radioactive elements (related to the half-life of an element). As well as appearing on Gordon's suit, the symbol replaces the letter "a" in the game title (Hλlf-Life) and is the name of the complex in the Black Mesa Research Facility where teleportation experiments are conducted in the first game. The Lambda symbol is also seen in Half-Life 2 as a marking of the human resistance, seen close to hidden supplies and on the armbands of better equipped resistance fighters.
Peptide PHI, also known as peptide histidine isoleucine, is a peptide which functions as a hormone. This peptide contains a composition of 27 amino acids with histidine on the N-terminus and isoleucine on the C-terminus. It was originally isolated from the mammalian small intestine amongst mammalian neurons called intramural neurons which function in the motor activity of the intestinal walls. An example of this was revealed in a study that demonstrated that this peptide regulates water and electrolyte transportation in the human jejunum; similar to its inhibitory effects on fluid absorption in the small intestine of pigs and rats. Peptide histidine isoleucine (PHI) is part of family that plays a vital role in the cell growth rate such as in the intestine as well as in brain. It was derived from glucagon family called the pituitary adenylate cyclase-activating polypeptide (PACAP) and it has an amino acid sequence homology to vasoactive intestinal peptide, secretin, glucagon, and other growth hormone releasing factor. Human studies have shown that the release of PHI into the stomach regulates the neuroendocrine cell processes that affect gastrointestinal physiology. This peptide is present within the central nervous system that help regulate food consumption behavior, while at peripheral nervous system this peptide accumulates in the stomach which controls the digestion of food. It also plays a role in the regulation of prolactin in humans.
In early 1954, he wrote the article "Cobalt 60 – Danger or Blessing for Mankind?", about the misuse of atomic energy, which was widely reprinted and transmitted in the radio in Germany, Norway, Austria, and Denmark, and in an English version worldwide via the BBC. The international reaction was encouraging. The following year he initiated and organised the Mainau Declaration of 1955, in which he and other international Nobel Prize-winners called attention to the dangers of atomic weapons and urgently warned the nations of the world against the use of "force as a final resort", and which was issued a week after the similar Russell-Einstein Manifesto. In 1956, Hahn repeated his appeal with the signature of 52 of his Nobel colleagues from all parts of the world. Hahn was also instrumental in and one of the authors of the Göttingen Manifesto of 13 April 1957, in which, together with 17 leading German atomic scientists, he protested against a proposed nuclear arming of the West German armed forces (Bundeswehr). This resulted in Hahn receiving an invitation to meet the Chancellor of Germany, Konrad Adenauer and other senior officials, including the Defense Minister, Franz Josef Strauss, and Generals Hans Speidel and Adolf Heusinger (who had both been generals in the Nazi era). The two generals argued that the Bundeswehr needed nuclear weapons, and Adenauer accepted their advice. A communiqué was drafted that said that the Federal Republic did not manufacture nuclear weapons, and would not ask its scientists to do so.
=== Twenty-first century === In the twenty-first century, the aim has been to develop more permanent beak trimming (although repeat trimming may be required), using electrically heated blades in a beak trimming machine, to provide a self-cauterizing cut. By 2012 there were four widely used methods of beak trimming: hot blade, cold blade (including scissors or secateurs), electrical (the Bio-beaker) and infrared. The latter two methods usually remove only the tip of the beak and do not leave an open wound; therefore they may offer improvements in welfare. Other approaches such as the use of lasers, freeze drying and chemical retardation have been investigated but are not in widespread use. The infrared method directs a strong source of heat into the inner tissue of the beak and after a few weeks, the tip of the upper and lower beak dies and drops off making the beak shorter with blunt tips. The Bio-beaker, which uses an electric current to burn a small hole in the upper beak, is the preferred method for trimming the beaks of turkeys. The Farm Animal Welfare Council (FAWC) wrote regarding beak trimming of turkeys that cold cutting was the most accurate method, but that substantial re-growth of the beak occurred; although the Bio-beaker limited beak re-growth, it was less accurate. It was considered that the hot cut was the most distressing procedure for turkeys. In the UK, beak trimming of layer hens normally occurs at 1-day of age at the same time as the chick is being sexed and vaccinated.
Sources: en.wikipedia.org
Linear RGD peptides suffer from low binding affinity, rapid degradation by proteases, and lack of specificity for integrin type. RGD can be cyclized, or made into a cyclic compound, via disulfide, thioether, or rigid aromatic ring linkers. This leads to an increase in binding affinity and selectivity for integrin αVβ3 relative to αIIBβ3. For example, the cyclic peptide ACDCRGDCFCG, also known as RGD4C, was shown to be 200-fold more potent than commonly used linear RGD peptides. The structural rigidity of cyclic RGD peptides improves their binding properties and prevents degradation at the highly susceptible aspartic acid residue, thereby increasing their stability. Many RGD derivative drugs and diagnostics are cyclized, including Eptifibatide, Cilengitide, CEND-1, and 18F-Galacto-RGD, and 18F-Fluciclatide-RGD.
Integrator complex subunit 15, also known as C7orf26, is a protein encoded in humans by the INTS15 gene. Based on properties of c7orf26 and its conservation over a long period of time, its suggested function is targeted for the cytoplasm and it is predicted to play a role in regulating transcription. Chromosome 7 is one of the 23 pairs of chromosomes in the human body, and spans about 159 million base pairs and represents about 5-5.5% of the total DNA in cells. Changes to the structure of chromosome 7 can result in a number of genetic abnormalities, including Williams Syndrome which causes structural and cosmetic changes to the human body, ultimately resulting in a shorter lifespan. There are hundreds of known open reading frames (ORF) along the domain of chromosome 7, however there is not much known about the 26th reading frame, which is of considerable interest. Currently, two isoforms of c7orf26 are known in Homo Sapiens and are referred to as isoforms 1 and 2, respectively.
Americium-241 (241Am, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of 432.6 years. 241Am is the most common isotope of americium as well as the most prevalent americium isotope in radioactive waste. It is used in ionization-type smoke detectors and is a potential fuel for long-lifetime radioisotope thermoelectric generators (RTGs). Its common parent nuclides are 241Pu (by beta decay), 241Cm (by electron capture), and 245Bk (by alpha decay). 241Am is fissile, with the critical mass of a bare sphere of 57.6–75.6 kilograms (127.0–166.7 lb) (diameter of 19–21 centimetres (7.5–8.3 in)). Americium-241 has a specific activity of 3.43 Ci/g (126.91 GBq/g). It is commonly found in the form of americium-241 dioxide (241AmO2). The presence of 241Am in plutonium is determined by the original concentration of plutonium-241 (which decays to it) and its age. Older samples of plutonium containing 241Pu build up 241Am and may require chemical removable of americium-241 (e.g., during reworking of plutonium's pits).
Sources: en.wikipedia.org
=== Biodegradation === In industrial wastewater treatment plants, EDTA can be degraded at about 80% using microorganisms. Resulting byproducts are ethylenediaminetriacetic acid and iminodiacetic acid (IDA) – suggesting that both the backbone and acetyl groups were attacked. Some microorganisms have even been discovered to form nitrates out of EDTA, but they function optimally at moderately alkaline conditions of pH 9.0–9.5. Several bacterial strains isolated from sewage treatment plants efficiently degrade EDTA. Specific strains include Agrobacterium radiobacter ATCC 55002 and the sub-branches of Pseudomonadota like BNC1, BNC2, and strain DSM 9103. The three strains share similar properties of aerobic respiration and are classified as gram-negative bacteria. Unlike photolysis, the chelated species is not exclusive to iron(III) in order to be degraded. Rather, each strain uniquely consumes varying metal–EDTA complexes through several enzymatic pathways. Agrobacterium radiobacter only degrades Fe(III) EDTA while BNC1 and DSM 9103 are not capable of degrading iron(III) EDTA and are more suited for calcium, barium, magnesium and manganese(II) complexes. EDTA complexes require dissociation before degradation.
This species is of typical tetra shape but grows to a maximum overall length of approximately 2 cm (0.8 in) to 3 cm (1.2 in). Most exhibit striking orange and reddish coloration with mild translucency near the pelvic fin. The eye frequently mirrors the color of the fish and is outlined in black. The fish's natural diet consist of small invertebrates and plants. Although somewhat hard to find in fish stores, H. amandae is commonly kept as an aquarium fish by hobbyists.
=== Sepsis === IGFBP-3 has been implicated in the regulation of cell growth, immune response, and endothelial integrity. In patients with sepsis, reduced serum levels of IGFBP-3 have been associated with increased mortality and greater immune suppression. A 2025 prospective study on 139 patients with microbiologically confirmed sepsis found that baseline IGFBP-3 concentrations below 10.64 pg/mL were independently associated with higher 30-day (28% vs. 10%) and 1-year mortality (69% vs. 35%) compared to patients with higher levels. These patients also exhibited lower lymphocyte counts, increased interleukin-6 levels, and more frequent polymicrobial infections, suggesting a phenotype characterized by immunosuppression and gut barrier dysfunction. IGFBP-3 had an area under the ROC curve (AUROC) of 0.70 for predicting 1-year mortality, outperforming other biomarkers such as CRP, procalcitonin, IL-6, and lactate. When added to clinical models including age and SOFA score, IGFBP-3 significantly improved prognostic accuracy up to 365 days. Preclinical studies support its immunomodulatory and anti-apoptotic roles, and therapeutic strategies targeting the IGF-1/IGFBP-3 axis are under investigation.
==== Other nuclear receptors ==== DHEA does not bind to or activate the progesterone, glucocorticoid, or mineralocorticoid receptors. Other nuclear receptor targets of DHEA besides the androgen and estrogen receptors include the PPARα, PXR, and CAR. However, whereas DHEA is a ligand of the PPARα and PXR in rodents, it is not in humans. In addition to direct interactions, DHEA is thought to regulate a handful of other proteins via indirect, genomic mechanisms, including the enzymes CYP2C11 and 11β-HSD1 – the latter of which is essential for the biosynthesis of the glucocorticoids such as cortisol and has been suggested to be involved in the antiglucocorticoid effects of DHEA – and the carrier protein IGFBP1.
Sources: en.wikipedia.org
It is a seven-amino-acid peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, produced by chemical synthesis rather than extracted from biological tissue. Its design is based on tuftsin, a natural immunomodulatory tetrapeptide. The C-terminal Pro-Gly-Pro segment is a common stabilising motif in short regulatory peptides.
The core four residues correspond to tuftsin, which occurs naturally as part of immunoglobulin G. The full seven-residue sequence, however, is not a known endogenous peptide. It is a laboratory-designed analogue intended to combine tuftsin-like activity with greater resistance to breakdown.
No single receptor has been confirmed as the primary target. Reports describe involvement of the GABAergic system, interference with enkephalin degradation, and shifts in neurotrophic factor expression. Because these observations come from different models and assays, they have not yet been integrated into one accepted mechanism.
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.