If you have been reading about prohibited substance and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-07-28. Where a claim depends on a specific study, the study is described rather than over-claimed.
Detection in biological samples relies on mass spectrometry, typically liquid chromatography coupled to tandem mass spectrometry after peptide extraction and enrichment. Intact peptides can also be confirmed by high-resolution mass measurement together with fragmentation data. Detection windows in urine are short because the peptide is degraded by proteases and cleared quickly, and concentrations are low. Many jurisdictions treat the compound as a prohibited substance in sport, grouped with peptide hormones and related factors, while it is not an approved therapeutic product. Identity and purity statements therefore rest on certificates of analysis, ideally issued by an independent laboratory.
Material is normally supplied as a lyophilised powder in a sealed vial. The powder is hygroscopic, so exposure to humid air leads to water uptake, caking and gradual loss of the fluffy texture that indicates a good freeze-dry. Vials are best kept sealed with desiccant, protected from light and stored cold. Letting a cold vial warm to room temperature before opening reduces condensation on the contents. Purity is normally reported from a chromatographic run, and that figure applies to the batch as tested rather than to the vial after repeated opening.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white solid | Lyophilised cake or powder |
| Solubility class | Freely soluble in water | Aqueous buffers also used |
| Typical storage temperature | About -20 degrees Celsius | Dry, sealed and protected from light |
| Typical analytical method | Reversed-phase HPLC or LC-MS/MS | Used for purity, identity and quantification |
| Common synonyms | Thymosin beta-4 fragment | Also listed under fragment-based descriptions |
TB-500 is a shorthand label used in supplier catalogs and online discussion for a short synthetic peptide described as a fragment of thymosin beta-4. Most product listings present it as the N-terminally acetylated heptapeptide Ac-LKKTETQ, a sequence corresponding to the actin-binding region of the parent protein. The name is not a formal chemical designation and does not appear in standard nomenclature systems. Because labeling practices vary between vendors, two products sold under the same name may not contain the same molecule, and the stated sequence should be treated as a claim rather than a fixed definition.
Thymosin beta-4 is a naturally occurring protein of 43 amino acids found in most mammalian cells, where it binds actin monomers and influences filament dynamics. It was first isolated from thymus tissue in the early 1980s, and its actin-binding activity was later mapped to a short region near the N-terminus. The synthetic fragment sold as TB-500 was designed to reproduce that region rather than the full protein. Whether a short fragment reproduces the behavior of the intact molecule remains an open question, since the parent protein carries additional structural elements outside the binding region.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
Lyophilised material is stable for extended periods when kept dry and cold, and suppliers typically recommend storage well below freezing. Once dissolved, the peptide is handled at refrigeration temperatures and used within a short period, because peptide bonds and the acetylated terminus can be affected by repeated freeze-thaw cycles, proteases, or extreme pH. Bacteriostatic water and saline are both described as solvents, although preservatives can interfere with some analytical workflows. Reconstituted solutions are inspected for particulates before use.
Sports authorities classify the peptide as a prohibited substance, and it appears on the World Anti-Doping Agency list under peptide hormones, growth factors, and related substances. Racing jurisdictions for horses and dogs have issued separate restrictions, and several national bodies treat it as a controlled or prescription-only item. As a research chemical it is sold without a therapeutic indication, and labels usually state that the product is not for human or veterinary use. Regulatory treatment therefore varies by country.
TB-500 is a laboratory label applied to a short synthetic peptide that is widely described as a fragment of thymosin beta-4, an actin-binding protein present in most mammalian cells. Suppliers and review articles usually present TB-500 as the N-terminal region of that protein, but the exact sequence attached to the name is not consistent across sources. Some product descriptions list a seven-residue chain; others use the label loosely for the parent protein itself. Because of that variation, any technical discussion of TB-500 needs to state which sequence is meant.
Thymosin beta-4 contains 43 amino acids and has a reported molecular mass near 4963 Da. The short fragment most often associated with the TB-500 label, an acetylated chain beginning LKKTETQ, has a reported mass near 889 Da, so the two are easily separated in analytical work. Mass spectrometry and amino acid analysis can confirm which material is present in a given sample. Statements treating TB-500 and thymosin beta-4 as interchangeable are therefore imprecise, even though the two appear together in much of the same literature.
Animal work has examined the peptide in models of cardiac injury, skin wounding, and corneal repair, with reported outcomes covering cell migration, inflammatory cell influx, and tissue remodeling. Several of those experiments used the full-length protein or longer fragments instead of the seven-residue sequence, which makes direct comparison between reports difficult. Results are generally described as tissue-dependent, and effect sizes vary considerably across laboratories. Independent replication is uneven, so the overall picture is incomplete rather than settled.
Controlled human trials of the short fragment are scarce. Much of what appears in review articles is extrapolated from animal models or from studies of the parent protein, and literature searches return a larger body of cardiac and ophthalmic work on thymosin beta-4 than on the abbreviated peptide. Regulatory treatment differs by jurisdiction, and in several countries the material is handled as a research chemical rather than an approved therapeutic. Statements about human benefit should be read as provisional.
Another Half-Life 2 episode was developed by Junction Point Studios, led by Warren Spector. The episode showed how the town of Ravenholm from Half-Life 2 became infested with headcrabs and zombies, with the return of the character of Father Grigori. It included a "magnet gun", which fired projectiles that magnetized metal surfaces and attracted objects and enemies, and was used for combat and puzzles. Junction Point worked on the game for a year, producing enough content to demonstrate one section, and a vertical slice that demonstrated the magnet gun. Valve lost interest in the project and Junction Point, who had been acquired by Disney Interactive Studios partway through, canceled it to instead develop Epic Mickey. Screenshots appeared in early 2017.
=== Enhancement of learning and memory === The growth hormone secretagogue receptor may also be linked to learning and memory. First of all, the receptor is found in the hippocampus, the brain region responsible for long-term memory. Second, it was found that specifically activating the receptor in just the hippocampus increased both long-term potentiation (LTP) and dendritic spine density, two cellular phenomena thought to be involved in learning. Third, short-term calorie restriction, defined as a 30% reduction in caloric intake for two weeks, which naturally increases ghrelin levels and thus activates the receptor, was found to increase both performance on spatial learning tasks as well as neurogenesis in the adult hippocampus.
== In popular culture == A fictionalized version of the Black Dragon Society "featured in much of American popular culture". It appeared in Master Comics starting with issue 21, first published by Fawcett Comics on December 10, 1941. Initially displayed as an external threat, the Black Dragon Society was given elements of a fifth column after the attack on Pearl Harbor, which reflected the fear of subversion of American society by Japanese-Americans. In DC's All Star Comics from 1942 the Society functioned as an opponent of the Justice Society of America and were likewise presented as an example of "alleged Japanese American perfidy". Another fictionalized version of the Black Dragon Society is featured in the CBS television series Raven, where they are a ninja clan operating in Hawaii.
== Other forms of copper sulfate == Anhydrous copper(II) sulfate can be produced by dehydration of the commonly available pentahydrate copper sulfate. In nature, it is found as the very rare mineral known as chalcocyanite. The pentahydrate also occurs in nature as chalcanthite. Other rare copper sulfate minerals include bonattite (trihydrate), boothite (heptahydrate), and the monohydrate compound poitevinite. There are numerous other, more complex, copper(II) sulfate minerals known, with environmentally important basic copper(II) sulfates like langite and posnjakite.
Sources: en.wikipedia.org
=== Gram-negative bacteria === In Gram-negative bacteria, e.g. Escherichia coli, PDC consists of a central cubic core made up of 24 molecules of dihydrolipoyl transacetylase (E2). Up to 16 homodimers of pyruvate dehydrogenase (E1) and 8 homodimers of dihydrolipoyl dehydrogenase (E3) bind to the 24 peripheral subunit binding domains (PSBDs) of the E2 24-mer. In Gammaproteobacteria, the specificity of PSBD for binding either E1 or E3 is determined by the oligomeric state of PSBD. In each E2 homotrimer, two of the three PSBDs dimerize. While two E1 homodimers cooperatively bind dimeric PSBD, the remaining, unpaired PSBD specifically interacts with one E3 homodimer. PSBD dimerization thus determines the subunit composition of the pyruvate dehydrogenase complex when fully saturated with the peripheral subunits E1 and E3, which has a stoichiometry of E1:E2:E3 (monomers) = 32:24:16
== Characteristics == The genome of C. xerosis is approximately 2.7 million base pairs long with over 2,000 genes encoding proteins and a high G+C content. C. xerosis was found to contain a series of plasmids, one of which confers resistance to common antibiotics such as chloramphenicol, kanamycin, streptomycin, and tetracycline and was named pTP10. This plasmid has since been introduced into Bacillus subtilis and modified to generate several vectors for molecular cloning purposes. In addition to having resistance to many antibiotics itself, at least one strain of C. xerosis also appears capable of producing antimicrobial compounds. These can inhibit bacteria and fungi, but the strength of antimicrobial activity by this strain depends on the carbon sources available. Also, a petroleum ether extract from C. xerosis was found to decrease the growth rate of tumors in mice, increasing their lifespan while being nontoxic to healthy mice. A study in 1967 confirmed the ability of several strains of C. xerosis to form single-layer "clumps" of cells around gas bubbles when cultures of the bacteria are suspended in buffer solutions at low temperatures with vigorous stirring. This property was attributed to cell surface proteins.
Immunomodulators Inhibitors of protein kinases Opioids Analgesics Treatment of benign prostatic hyperplasia Antiadrenergic drugs Hormonal treatments Diuretics Antiretroviral therapy Antihistamines Antidepressants *"For most of the drugs that are likely to affect spermatogenesis and/or sperm parameters, the levels of scientific evidence are still insufficient (with the exception of Sirolimus, Sulfasalazine, exogenous testosterone, Finasteride and Cyproterone acetate, for which the levels of evidence are higher). In some cases, data in men do not even exist, and the toxicity of a drug for the male reproductive organs is determined solely on the basis of animal models." **"For a certain number of pharmaceutical molecules that are likely to affect the sexual function of men being treated, the actual imputability of the drug is often difficult to pinpoint owing to the effect of the illness itself on sexuality (cardiovascular disease and erectile dysfunction; depressive illness and loss of desire, etc.)" Furthermore, hyperthyroidism, an excess of thyroid hormones, has been associated with reduced semen volume, reduced sperm density, motility, and morphology. Studies in humans show that an excess of circulating thyroid hormones during thyrotoxicosis results in asthenozoospermia, oligozoospermia, and teratozoospermia. These abnormalities frequently associate with semen alterations like reduced semen volume.
Sources: en.wikipedia.org
Sealed, dry and protected from light at reduced temperature is the usual laboratory convention. Allowing a cold vial to reach room temperature before opening limits condensation. Repeated opening exposes the powder to moisture and should be minimised.
Reported purity reflects the batch tested, the chromatographic method used and whether an independent laboratory performed the work. Values quoted without method detail or a traceable certificate are difficult to compare directly.
Short peptides are rapidly broken down by proteases and appear at low concentrations in urine, so the detection window is narrow. Sensitive extraction combined with tandem mass spectrometry is typically required.
TB-500 is a trade-style label for a synthetic peptide connected to thymosin beta-4. It is sold mainly through research-chemical channels and is not a single chemically defined product across suppliers.