This is a working overview of Heptapeptide, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-04-05 and is reviewed periodically as new material appears.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter notation. Its structure consists of the immunomodulatory tetrapeptide tuftsin, Thr-Lys-Pro-Arg, extended at the carboxyl terminus by a Pro-Gly-Pro segment. The molecular formula is commonly given as C33H57N11O9, corresponding to a monoisotopic mass near 751.4 Da and an average molecular mass near 751.9 Da. All seven residues are proteinogenic amino acids, and the molecule carries no modified side chains or non-natural linkages.
The compound was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences during the 1980s and 1990s. The stated design goal was to retain the immunomodulatory and central nervous system activity attributed to tuftsin while improving resistance to enzymatic breakdown. Adding a proline-rich tail to the short parent peptide was a deliberate strategy, because proline residues restrict the conformations available to many peptidases. The same laboratory produced Semax, an ACTH fragment analog, and both compounds were developed in parallel as short, enzymatically stabilized peptides intended for intranasal use.
Selank is not a naturally occurring peptide and has no known endogenous counterpart in human physiology. Russian-language sources frequently call it TP-7, while English-language sources use the name Selank almost exclusively. Database indexing is uneven, partly because early reports appeared in regional journals that are not widely cataloged. Some summaries describe the material as a tuftsin analog and others as a synthetic heptapeptide; the labels overlap rather than conflict. Citing the primary sequence resolves ambiguity more reliably than the research or trade name alone.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
| Property | Value | Notes |
|---|---|---|
| Peptide sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues; tuftsin plus a Pro-Gly-Pro tail |
| Molecular formula | C33H57N11O9 | Commonly reported value for the free peptide |
| Monoisotopic mass | Roughly 751.4 Da | Average molecular mass near 751.9 Da |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Freely soluble in water | Also dissolves in saline and other polar solvents |
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.
Naming for this compound is not fully standardised in English sources. The spelling Selanc appears in some transliterations, and catalogue entries may instead list the peptide sequence itself as the identifier. Reference material sometimes groups it with other short synthetic peptides studied for behavioural effects, which can create confusion when citations are compared. Distinguishing the exact sequence from related tuftsin analogues is therefore a practical first step when reviewing any dataset or specification sheet.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated as TKPRPGP. It was designed as a structural analogue of tuftsin, a naturally occurring tetrapeptide released by enzymatic cleavage of the immunoglobulin heavy chain. The two additional proline residues at the C-terminal end extend the parent chain and change how the molecule behaves in solution. The free peptide has a calculated molecular mass of approximately 751.9 g/mol and is generally supplied as a lyophilised white to off-white powder.
Development work on the compound began in the 1980s and 1990s at the Institute of Molecular Genetics in Moscow, within the same research programme that produced the peptide Semax. Early investigators sought a tuftsin derivative with improved resistance to enzymatic breakdown and with activity in the central nervous system after peripheral administration. Most of the primary literature from this period was published in Russian, a factor that still shapes how easily the findings can be checked by outside groups.
=== Cases of poisoning === Despite the element's highly hazardous properties, circumstances in which polonium poisoning can occur are rare. Its extreme scarcity in nature, the short half-lives of all its isotopes, the specialised facilities and equipment needed to obtain any significant quantity, and safety precautions against laboratory accidents all make harmful exposure events unlikely. As such, only a handful of cases of radiation poisoning specifically attributable to polonium exposure have been confirmed.
Wallace, following on earlier work by de Candolle, Humboldt and Darwin, made major contributions to zoogeography. Because of his interest in the transmutation hypothesis, he paid particular attention to the geographical distribution of closely allied species during his field work first in South America and then in the Malay Archipelago. While in the archipelago he identified the Wallace line, which runs through the Spice Islands dividing the fauna of the archipelago between an Asian zone and a New Guinea/Australian zone. His key question, as to why the fauna of islands with such similar climates should be so different, could only be answered by considering their origin. In 1876 he wrote The Geographical Distribution of Animals, which was the standard reference work for over half a century, and a sequel, Island Life, in 1880 that focused on island biogeography. He extended the six-zone system developed by Philip Sclater for describing the geographical distribution of birds to animals of all kinds. His method of tabulating data on animal groups in geographic zones highlighted the discontinuities; and his appreciation of evolution allowed him to propose rational explanations, which had not been done before.
In order for the male genitalia to develop properly in humans, both the classical and backdoor pathways are essential as means of DHT biosynthesis. Deficiencies in the backdoor pathway that converts 17OHP or P4 into DHT can result in undervirilization of the male fetus. This underviriliztion may happen because placental P4 acts as an important precursor to fetal DHT specifically within the backdoor pathway that should not be disrupted. Undervirilization refers to an incomplete masculinization of the male fetus. This condition can have consequences such as ambiguous genitalia or underdeveloped reproductive organs including the penis and testes. These conditions may impact fertility, sexual function, and can also affect an individual's overall gender identity later in life. A case study involving five individuals with a 46,XY (male) chromosomal pattern from two families revealed that their DSD, manifested in unusual genital appearance, was caused by mutations in the AKR1C2 and/or AKR1C4 genes. These genes are exclusively involved in the backdoor pathway of dihydrotestosterone (DHT) production. Mutations in the AKR1C3 and genes involved in the classical androgen pathway were excluded as the causes for the atypical genital appearance. Interestingly, their female relatives with a 46,XX chromosomal pattern who had the same mutations exhibited normal physical characteristics and fertility. Although both AKR1C2 and AKR1C4 enzymes are needed for DHT synthesis in a backdoor pathway, the study found that mutations in AKR1C2 only were sufficient for disruption.
Sources: en.wikipedia.org
=== In plants === In plants, glutathione plays a role in stress response. It is a component of the glutathione-ascorbate cycle, a system that reduces poisonous hydrogen peroxide. It is the precursor of phytochelatins, glutathione oligomers that chelate heavy metals such as cadmium. Glutathione is required for efficient defense against plant pathogens such as Pseudomonas syringae and Phytophthora brassicae. Adenylyl-sulfate reductase, an enzyme of the sulfur assimilation pathway, uses glutathione as an electron donor. Other enzymes using glutathione as a substrate are glutaredoxins. These small oxidoreductases are involved in flower development, salicylic acid, and plant defense signalling.
A Komodo dragon may attempt to speed up the process by ramming the carcass against a tree to force it down its throat, sometimes ramming so forcefully that the tree is knocked down. A small tube under the tongue that connects to the lungs allows it to breathe while swallowing. After eating up to 80% of its body mass in one meal, it drags itself to a sunny location to speed digestion, as the food could rot and poison the dragon if left undigested in its stomach for too long. Because of their slow metabolism, large dragons can survive on as few as 12 meals a year. After digestion, the Komodo dragon regurgitates a mass of horns, hair, and teeth known as the gastric pellet, which is covered in malodorous mucus. After regurgitating the gastric pellet, it rubs its face in the dirt or on bushes to get rid of the mucus.
=== Kinetics and transduction === The first demonstration that NAADP levels increase in response to an extracellular stimulus arose from studying sea urchin fertilization (NAADP changed in both the eggs and sperm upon contact). Subsequently, other cell types have followed suit, as exemplified by the pancreas (acinar and beta cells), T-cells, and smooth muscle. Levels increase very rapidly — and possibly precede the increase in the other messengers IP3 and cADPR— but can be very transient (spiking and returning to basal levels within seconds). The transduction mechanisms that couple cell stimuli to such NAADP increases are ill-defined, with some suggestions of cyclic AMP or cytosolic Ca2+ itself stimulating synthesis.
== See also == Bibliography of veganism and vegetarianism European Vegetarian Union International Vegetarian Union List of vegetarians Plant-based diet ProVeg International Vegetarian and vegan symbolism Vegetarian cuisine Vegetarian Diet Pyramid Vegetarian nutrition Women and vegetarianism and veganism advocacy
Sources: en.wikipedia.org
== Toxicodynamics == Apamin is the smallest neurotoxin polypeptide known, and the only one that passes the blood-brain barrier. Apamin thus reaches its target organ, the central nervous system. Here it inhibits small-conductance Ca2+-activated K+ channels (SK channels) in neurons. These channels are responsible for the afterhyperpolarizations that follow action potentials, and therefore regulate the repetitive firing frequency. Three different types of SK channels show different characteristics. Only SK2 and SK3 are blocked by apamin, whereas SK1 is apamin insensitive. SK channels function as a tetramer of subunits. Heteromers have intermediate sensitivity. SK channels are activated by the binding of intracellular Ca2+ to the protein calmodulin, which is constitutively associated to the channel. Transport of potassium ions out of the cell along their concentration gradient causes the membrane potential to become more negative. The SK channels are present in a wide range of excitable and non-excitable cells, including cells in the central nervous system, intestinal myocytes, endothelial cells, and hepatocytes. Binding of apamin to SK channels is mediated by amino acids in the pore region as well as extracellular amino acids of the SK channel. It is likely that the inhibition of SK channels is caused by blocking of the pore region, which hinders the transport of potassium ions. This will increase the neuronal excitability and lower the threshold for generating an action potential. Other toxins that block SK channels are tamapin and scyllatoxin.
In certain areas of the world, like Ethiopia where this was studied extensively, as the cows needed to intake more nutrition to balance out their milk production, there was also an increased level of chemical fertilizers and heavy metal traces found in the milk due to increased exposure to agricultural chemicals. These chemicals can then easily be passed on to humans and lead to a contaminated milk supply. BST increases the longevity or the activity of the mammary cell leading to higher milk production and some other non-desirable side effects. Despite public controversy of the use of growth hormones in food-producing animals, the number of violations has decreased substantially in the past two decades. For comparison, the level of antibiotic-residue detected in bulk milk tank trucks in 2012 was one fifth the level that it was in 1996. As reported by the USDA, the US pattern for milk BTSCC declined steadily from 316,000 cells per mL of milk in 2001 to 224,000 cells/mL in 2010 and 206,000 cells/mL in 2011 (USDA, 2013). Mammary health in the animals themselves has improved over this time period as well as the overall health of the dairy herd in general. This is mostly attributed to better application methods of rBST and a better understanding of how the hormone affects the animals.
Other economic reforms passed by the government included the creation of a unified modern currency based on the Japanese yen, banking, commercial and tax laws, stock exchanges, and a communications network. Establishment of a modern institutional framework conductive to an advanced capitalist economy took time, but was completed by the 1890s, by which time the government had largely relinquished direct control of the modernization process, primarily for budgetary reasons. The Land Tax Reform of 1873 was another significant fiscal reform by the Meiji government, establishing the right of private land ownership for the first time in Japan's history. Many of the former daimyo, whose pensions had been paid in a lump sum, benefited greatly through investments they made in emerging industries. Those who had been informally involved in foreign trade before the Meiji Restoration also flourished. Old bakufu-serving firms that clung to their traditional ways failed in the new business environment. The industrial economy continued to expand rapidly, until about 1920, due to inputs of advanced Western technology and large private investments. By World War I, Japan had become a major industrial nation.
==== β-carotene safety ==== No adverse effects other than carotenemia have been reported for consumption of β-carotene rich foods. Supplementation with β-carotene does not cause hypervitaminosis A. Two large clinical trials (ATBC and CARET) were conducted in tobacco smokers to see if years of β-carotene supplementation at 20 or 30 mg/day in oil-filled capsules would reduce the risk of lung cancer. These trials were implemented because observational studies had reported a lower incidence of lung cancer in tobacco smokers who had diets higher in β-carotene. Unexpectedly, high-dose β-carotene or retinol supplementation resulted in a higher incidence of lung cancer and of total mortality due to cardiac mortality. Taking this and other evidence into consideration, the U.S. Institute of Medicine decided not to set a Tolerable Upper Intake Level (UL) for β-carotene. The European Food Safety Authority, acting for the European Union, also decided not to set a UL for β-carotene.
During the Napoleonic Wars, the United States, Sweden, and Sicily fought against the Barbary pirates in the Mediterranean. The Barbary wars were a conflict between the United States and the North African States (Tripoli, Algiers, Tunis, and Morocco).
Sources: en.wikipedia.org
The sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code. It combines the tetrapeptide tuftsin with a carboxyl-terminal Pro-Gly-Pro extension. This full sequence identifies the molecule more precisely than the research name.
No peptide with this exact sequence has been identified as an endogenous substance. It is a laboratory-designed analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The Pro-Gly-Pro extension has no known natural source.
Proline introduces conformational constraints that make a peptide less accessible to common peptidases. This is a standard stabilization strategy in peptide design. The added residues also increase the distance between the active tuftsin portion and typical cleavage sites.
Reports describe effects on GABA-A receptor expression, monoamine turnover, and neurotrophic factor levels. These are proposed mechanisms drawn mainly from animal models. No single molecular target has been established.