Ac-LKKTETQ raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-06-07. Anything still debated is marked as such rather than presented as settled.
TB-500 is a synthetic heptapeptide with the sequence Ac-LKKTETQ. It corresponds to a short N-terminal region of thymosin beta-4, a 43-amino-acid protein found in many cell types. The fragment contains an actin-binding motif, which is one reason it appears in laboratory studies of cell migration and cytoskeletal dynamics. TB-500 is not the full-length protein and is produced as a research chemical rather than an approved therapeutic agent. Its molecular weight is approximately 889 Da.
Several names appear in scientific and commercial contexts for this peptide. The label TB-500 is informal and does not follow standard biochemical nomenclature. Research articles more often describe the compound as a thymosin beta-4 fragment, Tβ4 fragment, or by its sequence Ac-LKKTETQ. Confusing TB-500 with full-length thymosin beta-4 can lead to incorrect assumptions about activity because the fragment lacks the remaining residues of the parent protein. The relationship between fragment and parent protein remains an active area of study.
Regulatory status differs by country, but TB-500 is not an approved pharmaceutical in major jurisdictions. It is commonly sold as a research chemical for laboratory use, which places responsibility for identity and purity on the supplier and the laboratory. Published human data are limited, and most reports involve preclinical models or cell culture. Questions about whether the fragment mimics all actions of thymosin beta-4, and under which conditions, remain open. Independent verification of any material is therefore a practical requirement in research settings.
The fragment most often associated with the name carries the sequence Ac-LKKTETQ, matching residues 17 through 23 of thymosin beta-4. That region holds the actin-binding motif responsible for much of the parent protein's biochemical activity. Apart from N-terminal acetylation the peptide is unmodified and contains no disulfide bonds, so it shows little ordered secondary structure in solution. Full-length thymosin beta-4 is instead a 43-residue polypeptide of roughly 4.9 kDa found widely across mammalian cell types.
Material sold under this label typically arrives as a freeze-dried powder in a sealed vial with a certificate of analysis. Such certificates usually report reversed-phase chromatography purity plus a mass confirmation, and stated purities commonly sit between 95 and 99 percent. Counter-ion identity, residual trifluoroacetate, water content, and peptide net weight are separate specifications that a certificate may or may not include. A purity figure alone does not establish sequence identity, so independent mass verification remains the practical check.
The designation TB-500 circulates in laboratory and catalog contexts without a single agreed definition. Most product listings apply it to an N-terminally acetylated seven-residue fragment of thymosin beta-4, while other listings attach the same label to the full 43-residue protein. Because the term is commercial rather than systematic, two entries bearing identical names may describe different molecules. Any documentation should therefore state which sequence a given sample is claimed to contain.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H68N10O14 | Calculated for the acetylated heptapeptide |
| Molecular weight | ~889 Da | Monoisotopic mass approximately 889.0 Da |
| Amino acid sequence | Ac-LKKTETQ | N-terminal acetylated seven-residue peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Water-soluble | Peptides of this size generally dissolve in aqueous media |
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.
TB-500 is a synthetic peptide whose sequence corresponds to a short fragment near the N-terminus of thymosin beta-4, a small protein present in most mammalian cells. The fragment is commonly cited as containing the actin-binding region of the parent molecule, which is why it appears in laboratory work on cell migration and tissue repair. Suppliers distribute it as a lyophilised powder intended for research use. Its identity is defined by amino acid sequence and by the presence of an acetyl group on the N-terminal residue.
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.
Dry peptide powder is commonly kept at −20 °C in a desiccated container away from light, a practice that limits moisture uptake and oxidation. Once dissolved, solutions are generally held at 2–8 °C for short periods or frozen at −20 °C or lower for longer storage, with repeated freeze-thaw cycles avoided. Hydrolysis and oxidation are the main degradation routes for peptides in solution, and both accelerate at higher temperature or extreme pH. Published stability data specific to TB-500 are limited, so shelf life should be treated as uncertain.
Identity and purity checks for peptide material typically combine reversed-phase high-performance liquid chromatography with mass measurement, since retention time alone cannot confirm a sequence. Mass measurement verifies the expected molecular mass within instrument tolerance, while chromatographic peak area provides a purity estimate. Anti-doping analysis of urine uses related but more sensitive workflows, sometimes after solid-phase extraction. For research material, batch documentation, certificate content, and independent testing are common points of scrutiny, because supply chains outside pharmaceutical regulation vary widely in the paperwork they provide.
== tRNA/synthetase pair == Another key element is the tRNA/synthetase pair. The orthologous set of synthetase and tRNA can be mutated and screened through directed evolution to charge the tRNA with a different, even novel, amino acid. Mutations to the plasmid containing the pair can be introduced by error-prone PCR or through degenerate primers for the synthetase's active site. Selection involves multiple rounds of a two-step process, where the plasmid is transferred into cells expressing chloramphenicol acetyl transferase with a premature amber codon. In the presence of toxic chloramphenicol and the non-natural amino acid, the surviving cells will have overridden the amber codon using the orthogonal tRNA aminoacylated with either the standard amino acids or the non-natural one. To remove the former, the plasmid is inserted into cells with a barnase gene (toxic) with a premature amber codon but without the non-natural amino acid, removing all the orthogonal syntheses that do not specifically recognize the non-natural amino acid. In addition to the recoding of the tRNA to a different codon, they can be mutated to recognize a four-base codon, allowing additional free coding options. The non-natural amino acid, as a result, introduces diverse physicochemical and biological properties in order to be used as a tool to explore protein structure and function or to create novel or enhanced protein for practical purposes.
1989–1991 – 1.3 L (1,323 cc) B3, 1 barrel, 8-valve, 76 PS (56 kW) / 101 N⋅m (74 lb⋅ft) 1991–1994 – 1.3 L (1,323 cc) B3, EGI-S, 8-valve, 79 PS (58 kW) / 103 N⋅m (76 lb⋅ft) 1989–1991 – 1.5 L (1,498 cc) B5-M, carburetor, 16-valve, 91 PS (67 kW) / 122 N⋅m (90 lb⋅ft) 1990–1994 – 1.5 L (1,498 cc) B5-MI, EGI-S, 16-valve 94 PS (69 kW) / 123 N⋅m (91 lb⋅ft) 1989–1991 – 1.5 L (1,498 cc) B5-DE, EFi, 16-valve DOHC, 110 PS (81 kW) / 127 N⋅m (94 lb⋅ft) 1991–1994 – 1.5 L (1,498 cc) B5-DE, EFi, 16-valve DOHC, 115–120 PS (85–88 kW) / 132 N⋅m (97 lb⋅ft) (lower power for AT cars) 1989–1991 – 1.6 L (1,597 cc) B6, 1 barrel, 8-valve, 85 hp (63 kW; 86 PS) / 92 lb⋅ft (125 N⋅m) 1989–1994 – 1.6 L (1,597 cc) B6, carburetor, 16-valve, SOHC, 103 hp (77 kW; 104 PS) / 108 lb⋅ft (146 N⋅m) 1989–1994 – 1.8 L (1,839 cc) BP, FI, 16-valve DOHC, 140 hp (104 kW; 142 PS) / 118 lb⋅ft (160 N⋅m) 1989–1994 – 1.8 L (1,839 cc) BPT, FI, 16-valve DOHC, turbo, 180 PS (132 kW) / 237 N⋅m (175 lb⋅ft) (Familia GT-X) 1991–1994 – 1.8 L (1,839 cc) B8, FI, 16-valve SOHC, 103 hp (77 kW) 1992–1993 – 1.8 L (1,839 cc) BPD, FI, 16-valve DOHC, turbo, 210 PS (154 kW) / 255 N⋅m (188 lb⋅ft) (Familia GT-R & GT-Ae) 1989–1994 – 1.7 L (1,720 cc) PN, Diesel, 8-valve, 57 PS (42 kW) / 112 N⋅m (83 lb⋅ft) (European specs)
=== 1960s === 1960: Rosalyn Yalow received the Nobel Prize in Physiology or Medicine "for the development of radioimmunoassays of peptide hormones" along with Roger Guillemin and Andrew V. Schally who received it "for their discoveries concerning the peptide hormone production of the brain". 1962: Katherine Johnson performed the calculations for the NASA orbital mission, launching John Glenn as the first person into orbit and returning them safely. 1963: Maria Goeppert Mayer became the first American woman to receive a Nobel Prize in Physics; she shared the prize with J. Hans D. Jensen "for their discoveries concerning nuclear shell structure” and Eugene Paul Wigner "for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles". She was born in Poland, but became a U.S. citizen in 1933. 1965: Sister Mary Kenneth Keller became the first American woman to earn a Ph.D. in Computer Science. Her thesis was titled "Inductive Inference on Computer Generated Patterns."
=== DNA repair === Two classical DNA repair pathways, nucleotide excision repair and base excision repair, are present in hydra, and these repair pathways facilitate unhindered reproduction. The identification of these pathways in hydra is based, in part, on the presence in the hydra genome of genes homologous to genes in other genetically well studied species that have been demonstrated to play key roles in these DNA repair pathways.
Sources: en.wikipedia.org
Alza Corporation was an American pharmaceutical and medical systems company. Founded in 1968 by Dr. Alejandro Zaffaroni; the company's name is a portmanteau of his name. Alza was a major pioneer in the field of drug delivery systems, bringing over 20 prescription pharmaceutical products to market, and employing about 10,000 people during 20 years. In 2001, Alza was acquired by Johnson & Johnson via a stock-for-stock transaction worth US$10.5 billion. The company owns the patents on the following delivery platforms: Alzamer Depot D-Trans DUROS implant E-Trans electrotransport OROS (Osmotic Release Oral System) Macroflux transdermal system Stealth liposomal
=== Availability === Midazolam is available in the United States as a syrup or as an injectable solution. Dormicum brand midazolam is marketed by Roche as white, oval, 7.5 mg tablets in boxes of two or three blister strips of 10 tablets, and as blue, oval, 15 mg tablets in boxes of two (Dormonid 3x) blister strips of 10 tablets. The tablets are imprinted with "Roche" on one side and the dose of the tablet on the other side. Dormicum is also available as 1, 3, and 10 mL ampoules at a concentration of 5 mg/mL. Another manufacturer, Novell Pharmaceutical Laboratories, makes it available as Miloz in 3 and 5 mL ampoules. Midazolam is the only water-soluble benzodiazepine available. Another maker is Roxane Laboratories; the product in an oral solution, midazolam HCl Syrup, 2 mg/mL clear, in a red to purplish-red syrup, cherry in flavor. It becomes soluble when the injectable solution is buffered to a pH of 2.9–3.7. Midazolam is also available in liquid form. It can be administered intramuscularly, intravenously, intrathecally, intranasally, buccally, or orally.
To lessen the risk of developing ketoacidosis (a serious condition in which the body produces high levels of blood acids called ketones) after surgery, the FDA approved changes to the prescribing information for SGLT2 inhibitor diabetes medicines to recommend they be stopped temporarily before scheduled surgery. Canagliflozin, dapagliflozin, and empagliflozin should each be stopped at least three days before, and ertugliflozin should be stopped at least four days before scheduled surgery. Symptoms of ketoacidosis include nausea, vomiting, abdominal pain, tiredness, and trouble breathing.
Used in biological sequence analysis: Genbank, UniProt Used in structure analysis: Protein Data Bank (PDB) Used in finding Protein Families and Motif Finding: InterPro, Pfam Used for Next Generation Sequencing: Sequence Read Archive Used in Network Analysis: Metabolic Pathway Databases (KEGG, BioCyc), Interaction Analysis Databases, Functional Networks Used in design of synthetic genetic circuits: GenoCAD
B'Tselem also argues that the restrictions on ill, wounded and pregnant Palestinians seeking acute medical care is in contravention of international law that states that medical professionals and the sick must be granted open passage. While Israeli Supreme Court has deemed the measures acceptable for security reasons, Haaretz's Amira Hass argues this policy defies one of the principles of the Oslo Accords, which states that Gaza and the West Bank constitute a single geographic unit. Strained intercommunal relations in Northern Ireland between Irish Catholics and the descendants of Protestant settlers from England and Scotland have resulted in de facto internal checkpoints. The peace lines are an internal border security measure to separate predominantly republican and nationalist Catholic neighbourhoods from predominantly loyalist and unionist Protestant neighbourhoods. They have been in place in some form or another since the end of The Troubles in 1998, with the Good Friday Agreement. The majority of peace walls are located in Belfast, but they also exist in Derry, Portadown, and Lurgan, with more than 32 kilometres (20 miles) of walls in Northern Ireland. The peace lines range in length from a few hundred metres to over 5 kilometres. They may be made of iron, brick, steel, or a combination of the three and are up to 8 metres (26 feet) high. Some have gates in them (sometimes staffed by police) that allow passage during daylight but are closed at night.
Sources: en.wikipedia.org
TB-500 is a synthetic heptapeptide corresponding to a fragment of thymosin beta-4. It is used in laboratory research and is not an approved drug.
No. Thymosin beta-4 is a 43-amino-acid protein, while TB-500 represents only a short N-terminal segment. The two should not be treated as interchangeable in experimental design.
It is often called a thymosin beta-4 fragment, Tβ4 fragment, or Ac-LKKTETQ. The name TB-500 is mainly a commercial or catalog label rather than a formal chemical name.
Usually not, though usage overlaps. The label most often refers to a short acetylated fragment of the parent protein, while thymosin beta-4 itself is the full 43-residue molecule. Because suppliers vary, a sequence statement is needed to settle the question for any particular lot.