A practical reference on freeze-thaw: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-07-13. Anything still debated is marked as such rather than presented as settled.
Biological interest in this peptide centers on its relationship to actin dynamics. Thymosin beta-4 binds monomeric actin through an LKKTET motif, and a short sequence carrying that motif can compete with other actin-binding proteins in cell-free preparations. Investigators propose that such competition shifts the balance between filament assembly and disassembly, which in turn affects how readily a cell extends protrusions and migrates. Most of the supporting observations come from cultured cells and purified protein systems rather than from intact organisms.
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.
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 |
|---|---|---|
| Common synonyms | Thymosin beta-4 fragment; TB4 fragment | Naming is inconsistent across suppliers and publications |
| Reported sequence | Ac-LKKTETQ | Corresponds to residues 17-23 of the parent protein |
| Frequently cited registry number | 77591-33-4 | Associated with full-length thymosin beta-4 rather than the fragment |
| Common supplied form | Freeze-dried solid | Often presented as an acetate or trifluoroacetate salt |
| Regulatory treatment | Varies by country | Frequently handled as a research chemical; not broadly approved as a therapeutic |
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
Purity and identity are separate measurements and are often confused. Reverse-phase high-performance liquid chromatography, usually with ultraviolet detection near 214 nanometres, reports the share of total peak area belonging to the target compound. Mass spectrometry by electrospray or matrix-assisted laser desorption then checks whether the observed mass matches the expected sequence. Neither measurement alone shows that a vial holds the intended peptide. Peptide content, meaning the fraction of vial mass that is genuine peptide rather than counter-ion, water or residual acid, is reported separately and is frequently lower than the stated purity figure.
The regulatory position is broadly consistent across major jurisdictions: no thymosin beta-4 fragment is an approved medicine, and laboratory material is commonly labelled as not intended for human consumption. Anti-doping rules in sport list thymosin beta-4 and its fragments among prohibited peptide hormones. Because these products travel through research-chemical channels rather than pharmaceutical supply chains, quality varies considerably between vendors. Independent testing of identity, purity and sterility is the only dependable check, and a certificate of analysis describes one batch rather than a supplier's whole catalogue.
Lyophilized peptide powder is normally held desiccated at −20 °C, with −80 °C used for longer storage periods. Allowing a sealed vial to reach room temperature before opening is standard practice, because condensation forming on cold powder introduces moisture. Once dissolved, solutions are typically kept cold and shielded from light. Repeated freeze-thaw cycles are avoided because they encourage aggregation and gradual loss of material. These conventions are general to synthetic peptides rather than unique to any one sequence.
The compound is most often distributed as a lyophilized powder, appearing white to off-white and forming a loose cake or fluffy solid. It is hygroscopic to some degree, so brief exposure to humid air can add water weight and complicate weighing. The peptide dissolves readily in water and in neutral aqueous buffers, and aqueous solubility is generally described as high, well above the concentrations used in typical assays. Some polar organic solvents are also usable, which matters when a concentrated stock is prepared before dilution into buffer.
Storage recommendations center on keeping the dry powder cold, dry, and dark. A freezer at -20 degrees Celsius or below is conventional, and desiccant is often included to limit moisture uptake. Once dissolved, the peptide is less stable, and solutions are typically kept frozen and thawed only once. Repeated freeze-thaw cycles are a common source of losses because they promote aggregation and adsorption to container surfaces. Working aliquots are therefore prepared in advance, and glass or low-binding plastic is usually preferred over ordinary laboratory plastic.
Identity and purity are assessed with a small set of standard techniques. Reverse-phase high-performance liquid chromatography gives a purity estimate from peak area, usually recorded at 214 or 220 nanometers, where the peptide bond absorbs. Mass spectrometry confirms the expected molecular mass and can reveal truncated or oxidized species. Amino acid analysis or tandem mass spectrometry sequencing can verify the sequence itself. Additional quality attributes include water content, residual trifluoroacetic acid carried over from purification, and endotoxin where the material is intended for biological work.
===== Pumpeninsulin ===== Velosulin® war ein Humaninsulin, das von Novo Nordisk speziell für die Verwendung in Insulinpumpen entwickelt wurde. Entgegen der für alle anderen Insulinpräparate geltenden Empfehlung, sie bei Kühlschranktemperaturen zu lagern, muss das in der Pumpe mitgeführte Insulin über mehrere Tage bei Umgebungstemperatur seine Wirksamkeit behalten. Hergestellt wurde es gentechnisch aus rekombinanter DNA in Saccharomyces cerevisiae. Hilfsstoffe: Zinkchlorid, Glycerol, m-Kresol, Dinatriumhydrogenphosphat-Dihydrat (als Puffersubstanz), Natriumhydroxid und/oder Salzsäure (zur Einstellung des pH-Wertes), Wasser für Injektionszwecke. Anfang Mai 2007 wurde Velosulin von Novo Nordisk vom Markt genommen. Ersatzweise wurde die Umstellung auf schnellwirkende Insulinanaloga empfohlen, da diese für eine optimale Blutzuckereinstellung besser geeignet seien und sich als ausreichend stabil zur Verwendung in Insulinpumpen erwiesen hätten.
==== Insulinanaloga ==== Normal- oder Altinsulin hat gegenüber dem Insulin aus der Bauchspeicheldrüse einen entscheidenden Nachteil: Die Insulinmoleküle sind in Sechsergruppen (Hexamere) angeordnet. Nach einigen Minuten zerfallen diese in Zweiergruppen (Dimere). Erst wenn diese endgültig in einzelne Moleküle zerfallen sind, wird das Insulin wirksam. Das Insulin in der Bauchspeicheldrüse wird dort zwar auch in Hexameren gespeichert, aber bei Bedarf werden Einzelmoleküle ins Blut entlassen und werden in der Leber innerhalb von Sekunden wirksam. Daher wurde versucht, Insuline zu finden, die schneller wirksam werden, um damit näher an die Wirkkurve des natürlichen Insulins heranzukommen. Die kurzwirksamen Insulinanaloga fluten rascher an und haben eine kürzere Wirkdauer als Normalinsulin. Ein Vorteil ist der Wegfall der Notwendigkeit von Zwischenmahlzeiten, die bei der Verwendung von Normalinsulin oft notwendig sind, um das Hypoglykämierisiko durch den „Insulinüberhang“ mehrere Stunden nach einer Hauptmahlzeit zu kompensieren. Eine zweite Forschungsrichtung ist die Entwicklung von Analog-Insulinen, die länger als das NPH-Insulin wirken. Bei beiden Richtungen wird versucht, das Ziel durch die Modifikation der Molekülstruktur zu erreichen.
===== Insulin lispro ===== Insulin lispro (manchmal auch Lyspro) war das erste Insulin, das dieses Ziel verwirklicht hat. In der EU zugelassene Injektionslösungen sind Humalog® (zugelassen am 30. April 1996, Eli Lilly and Company), Insulin lispro Sanofi® (zugelassen am 19. Juli 2017, Sanofi) und Lyumjev® (zugelassen am 24. März 2020, Eli Lilly and Company). Seit Ende 2005 bis April 2023 wurde es auch von Berlin-Chemie unter dem Handelsnamen Liprolog® vertrieben. Beim Insulin lispro sind die Aminosäuren an B28 und B29 vertauscht. Die neue Reihenfolge führt zum Namen.
Die Herstellung erfolgt gentechnisch aus rekombinanter DNA. Als Zusatzstoffe sind m-Kresol, Glycerol, Natriummonohydrogenphosphat, Zinkoxid, Wasser für Injektionszwecke, Natriumhydroxid oder Salzsäure zur pH-Wert-Einstellung beigefügt. Das Präparat ist zur Pumpentherapie zugelassen. Insulin lispro wird schneller durch das Unterhautfettgewebe transportiert und zerfällt auch schneller in Einzelmoleküle. Dadurch wird ein schnellerer Wirkbeginn und eine kürzere Wirkdauer erreicht. Das Medikament ist verschreibungsfähig. Das Präparat Lyumjev enthält Insulin lispro und die Hilfsstoffe Citrat und Treprostinil. Diese bewirken einen rascheren Wirkeintritt, indem sie die Permeabilität der Gefäße erhöhen und dadurch das Insulin schneller in die Blutbahn gelangen kann.
Sources: de.wikipedia.org
The leading proposal involves sequestration of monomeric actin, which would alter cytoskeletal turnover and cell movement. The actin-binding motif shared with the parent protein is central to that idea. Direct confirmation in whole organisms remains limited.
Very few controlled human studies focus on the seven-residue sequence itself. Most clinical data concern the full-length protein in cardiac or ophthalmic settings. Conclusions drawn for one form should not be assumed to transfer to the other.
Detection normally relies on reversed-phase liquid chromatography paired with mass spectrometry. Chromatographic retention time establishes the expected elution window, and the mass spectrum confirms the molecular ion. Immunoassays exist but can cross-react with related peptides.
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.