The short version of Ac-SDKP fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-09-13. Anything still debated is marked as such rather than presented as settled.
TB-500 is a synthetic peptide preparation marketed under a name derived from thymosin beta-4, a 43-residue actin-binding protein first isolated from thymus tissue. The full-length protein has a reported molecular mass near 4963 Da, while material sold as TB-500 is often described as a fragment containing the actin-binding motif LKKTETQ. Because suppliers use the name inconsistently, published sources sometimes refer to the same label as a fragment, a synthetic copy, or a related analog. This naming ambiguity complicates direct comparison of reports across studies.
Laboratory work on thymosin beta-4 describes binding to monomeric actin and effects on cell migration, angiogenesis, and inflammatory signaling in cultured cells. Animal models have examined skin, corneal, and cardiac repair after injury, with outcomes reported mainly in preclinical literature. Most of that evidence concerns the parent protein rather than preparations labelled TB-500, so extrapolation from animal findings to a specific commercial product remains uncertain. Whether the two behave identically in living systems has not been established in controlled human studies.
No major regulatory agency has approved TB-500 for therapeutic use, and it holds no pharmacopoeial monograph. The name appears on the World Anti-Doping Agency prohibited list within the class covering peptide hormones, growth factors, and related substances. Detection in doping control relies on mass spectrometric methods applied to urine, often after preparation steps that concentrate the analyte. Discussion of TB-500 therefore clusters in biochemistry, sports medicine, and anti-doping literature rather than in registered clinical trials.
Lyophilised peptide is normally reconstituted with sterile water or a neutral buffer shortly before use. Because repeated freeze-thaw cycles can degrade the material, dividing a reconstituted solution into single-use aliquots is a common practice. Working solutions are usually kept cold and protected from light. The exact shelf life depends on concentration, buffer composition, and handling, so it is often determined empirically rather than assumed.
Peptide bonds are susceptible to hydrolysis under extreme pH and to enzymatic cleavage if proteases are present. Heat, oxidising agents, and prolonged exposure to light also contribute to loss of material. Aggregation can occur at high concentrations or in certain buffer systems, and it may not be visible to the eye. Storage at -20 C or below is typical for both powder and aliquoted solutions, and desiccation of the powder is preferred.
| Property | Value | Notes |
|---|---|---|
| Molecular mass | Approximately 4963 Da for full-length thymosin beta-4 | Value applies to the parent protein; fragment products may differ |
| Appearance | White to off-white lyophilized powder | Typical form of supplied synthetic peptide |
| Solubility | Freely soluble in water | Polar peptide; dissolves readily in aqueous buffer |
| Storage of dry powder | −20 °C, desiccated, protected from light | Standard laboratory practice for peptides |
| Typical detection method | Liquid chromatography–tandem mass spectrometry | Used in purity testing and anti-doping analysis |
Full-length thymosin beta-4 consists of roughly forty-three amino acids and ranks among the more abundant small proteins in the cytoplasm. The fragment is much shorter, so it cannot reproduce every function attributed to the intact molecule. In cell culture, short actin-binding motifs can interfere with filament dynamics and cell movement, but such observations come from controlled experiments rather than from whole-animal work. Whether a truncated fragment produces the same effects as the parent protein remains an open question.
Interest in the peptide grew during the 2000s and 2010s, when studies of tendon and ligament injuries in horses reported changes in lesion size after treatment. Those reports circulated widely outside the scientific literature and shaped much of the current online discussion. Subsequent reviews noted inconsistent study design, small groups, and a shortage of independent replication. Popular descriptions often blur the line between the fragment, the complete protein, and unrelated growth factors, which complicates comparisons across sources.
Interest in the fragment grew during the 1990s and 2000s, when it moved from laboratory work into sports and supplement markets. Anti-doping bodies added thymosin beta-4 fragments to prohibited lists, and a small number of adverse analytical findings have been reported in competition testing. Published controlled human trials remain scarce. Most mechanistic evidence comes from cell culture and animal models, and those studies examine endpoints such as cell migration, wound closure and inflammation markers. That evidence supports research interest but does not establish clinical benefit, and broad regenerative claims should be read as unverified.
TB-500 is a short synthetic peptide sold under a trade name rather than a systematic chemical name. Suppliers usually describe it as a fragment of thymosin beta-4 and ship it as a lyophilised powder intended for laboratory use. Because the label is commercial, the exact sequence attributed to it is not fully consistent across catalogues, and some listings present a seven-residue peptide while others describe related fragments of similar length. It is not an approved medicine in any major jurisdiction, and it is handled as a research chemical.
Thymosin beta-4 itself is a natural peptide of 43 residues found in many cell types and body fluids. Its best-characterised function is binding and sequestering actin monomers, which influences cytoskeletal dynamics. The sequence most often associated with TB-500, LKKTETQ, corresponds to part of that actin-binding region. A different fragment, Ac-SDKP, is also derived from the same parent peptide and is studied in its own right, which is one reason discussions of thymosin fragments can become confusing. The two are structurally distinct and are not interchangeable.
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.
Old Time’s Sake (englisch für „um der alten Zeiten willen“) ist ein Lied des US-amerikanischen Rappers Eminem, auf dem auch sein Entdecker Dr. Dre zu hören ist. Der Song ist die vierte Singleauskopplung seines sechsten Studioalbums Relapse und wurde am 5. Mai 2009 ausschließlich zum Download veröffentlicht.
Im Track thematisieren Eminem und Dr. Dre vor allem ihre jahrelange und erfolgreiche Zusammenarbeit sowie den Konsum von Drogen. Beim Intro parodiert Eminem die Ansage eines Flugzeugpiloten und sagt, dass man nun die Höhe erreicht habe, um in der Kabine zu rauchen. Dr. Dre beginnt nun darüber zu rappen, dass er zusammen mit Eminem zurück sei und es kein vergleichbares Duo im Hip-Hop gebe. Eminem schlüpft währenddessen in die Rolle seines Alter Egos Slim Shady, das mit Kettensäge auf der Suche nach Opfern ist. In der von Eminem gerappten Hookline heißt es, dass beide sich um der alten Zeiten willen wieder zusammengetan haben, um weitere Hits zu produzieren. Im ebenfalls von Eminem interpretierten zweiten Vers spitzt sich der Drogenkonsum zu. Nun nimmt Slim Shady neben Marihuana auch Vicodin zu sich und äußert sich sexistisch gegenüber Frauen. Im dritten Vers konsumiert Slim Shady Wodka, Kreatin sowie Red Bull und macht anschließend ironische Anspielungen gegenüber R. Kelly, der einst wegen Kindesmissbrauchs angeklagt war, aber freigesprochen wurde. Dr. Dre glorifiziert seinen Marihuana-Konsum, der ihm die künstlerische Kreativität gegeben habe, um die Spitze der Charts zu erreichen. Daraufhin fragt Slim Shady, ob er etwas abhaben könne, weil es auch seinen Rap verbessere. Allerdings ist er schon so high, dass er in seine eigene Welt abdriftet und über Analsex phantasiert.
== Produktion == Der Beat des Liedes wurde von Eminems Entdecker und Produzent Dr. Dre, der ebenfalls auf dem Song zu hören ist, in Zusammenarbeit mit Mark Batson produziert. Dabei wurden keine Samples von Titeln anderer Künstler verwendet.
Sources: de.wikipedia.org
=== Covergestaltung === Das Singlecover zeigt Eminem in schwarzer Kleidung, die Arme zu beiden Seiten ausgebreitet. Im Vordergrund stehen die weißen Schriftzüge Eminem, Old Time’s Sake und Feat. Dr. Dre, wobei letzterer mit einem blauen Balken unterlegt ist. Der Hintergrund ist komplett in schwarz gehalten.
Sources: de.wikipedia.org
Not necessarily. TB-500 is a commercial label that suppliers apply to synthetic peptides described as thymosin beta-4 or a fragment of it. Published research most often studies the full-length protein, so statements about one do not automatically transfer to the other.
No. No major regulatory authority lists an approved product under this name, and no pharmacopoeial monograph exists for it. Material sold under the label is therefore supplied outside approved pharmaceutical channels, which affects the quality documentation available.
It falls within a prohibited class covering peptide hormones and growth factors, based on presumed effects on tissue repair and blood vessel formation. Anti-doping laboratories have published mass spectrometry methods for detecting thymosin beta-4 related peptides in urine samples.
The lyophilised powder is typically held at -20 C or lower in a dry, dark place. Reconstituted solutions are aliquoted and frozen to avoid repeated freeze-thaw cycles.