TB-500 (Thymosin β4 fragment / Thymosin Beta-4): preparation and storage
Intended for research use only. Not a medicinal product.
Contents (11 sections)
A trade name does not establish length
Primary analytical studies identified TB-500 as the N-acetylated 17-23 fragment of thymosin β4, Ac-LKKTETQ. This contains seven residues, whereas natural full-length Tβ4 contains 43. Current catalogues may also use TB-500 for the full molecule. This page therefore does not infer form from the trade name. Require the sequence, terminal groups, expected mass and the particular batch certificate. If the supplied material is full-length Tβ4, use its specification and separate handling guide; do not transfer short-fragment calculations.
The fragment has a different composition from full Tβ4
Ac-LKKTETQ contains no methionine, tryptophan or cysteine. Monitoring full-length Tβ4 Met6 oxidation therefore does not assess this fragment. That does not exclude every alteration pathway or establish indefinite stability. Analytical markers must match the seven-residue acetylated chain. Revisit a full-length-only method before switching to fragment material. Establish whether its signal detects Ac-LKKTETQ rather than residual full Tβ4 or another sample component.
What the primary studies actually identified
Ho and colleagues investigated a veterinary TB-500 preparation in 2012, measuring N-acetylated LKKTETQ and metabolites in equine plasma and urine. Esposito and colleagues independently described identification of this fragment in a product and synthesis of a corresponding standard. These are chemical and analytical findings for the described preparations, not proof of every current vial’s composition or therapeutic efficacy. Record both TB-500 and the confirmed chemical identity, Ac-LKKTETQ or full-length Tβ4 if that is what was established.
Ac-LKKTETQ requires acetylation checks
When the short fragment is confirmed, N-terminal acetylation and all seven residues matter. Unacetylated LKKTETQ is a different analyte. Identification studies used chromatography and mass spectrometry with retention-time and product-ion checks. The same principle applies to laboratory quality control: a general HPLC peak without identity confirmation is insufficient. Match calibration-solution preparation to extraction and the final matrix; recovery from plasma or culture medium is not equivalent to recovery from a clean buffer.
Mass calculations and working dilutions
An arithmetic example, not a solubility prescription: 2 mg in a final volume of 4 mL gives 0.5 mg/mL, or 500 micrograms/mL. Adding 20 microliters of that stock to 980 microliters of compatible matrix gives 10 micrograms/mL. Then 100 microliters of this solution plus 900 microliters of matrix gives 1 microgram/mL. Use the final volume in the calculation. If the certificate separately establishes peptide mass fraction, apply it according to the labeling convention, without correcting the mass twice. Molarity requires the molecular weight of the confirmed form; do not borrow a value from a related analogue.
An actin-binding motif is not the whole molecule
LKKTETQ lies in a functionally important Tβ4 region, but that motif does not establish that the fragment reproduces full-length stoichiometry or every property of the parent molecule. Test fragment function directly in actin experiments, treating full-length Tβ4 as a separate comparator. Migration assays also require proliferation and viability checks: faster scratch closure is not a direct actin-binding measurement. Match concentrations, exposure and medium across groups.
Extraction and metabolites change interpretation
Ho used ion-exchange solid-phase extraction followed by LC-MS. Parent fragment and metabolites were identified by retention time and major product-ion ratios. Another matrix needs renewed parameter and recovery checks. Low parent-molecule signal in a biological sample can reflect metabolism rather than poor original-vial dissolution. Additional forms in a clean control solution require a different explanation. Do not combine these situations into a general “TB-500 instability” claim without identifying where and when change occurred.
Recognizing form errors
Can Tβ4 molecular weight be used for Ac-LKKTETQ? It would give an incorrect molar concentration. Does an anti-Tβ4 antibody detect every TB-500 material? Recognition depends on the epitope; a short fragment may lack it. Does an equine-sample analytical paper establish your stock lifetime? It supports the identified analyte and method in its specified matrix, not universal stability. After storage, compare material with a standard of the same form; changed extraction recovery can mimic loss of peptide.
Analytical-standard stocks
The specification determines frozen dry-Ac-LKKTETQ storage and moisture protection; a short chain does not establish indefinite refrigerator stability. For LC-MS use, distinguish stock-solution, extraction-control and working-dilution checks. Spiking plasma before and after extraction helps separate preparation recovery from matrix effects. Cell experiments need separate functional controls because analytical-standard suitability does not guarantee an expected cell response. A BPC-157 mixture is not a pure TB-500 standard without independent quantification and separation of both components.
Sources and scope
- Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography-mass spectrometry
- Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential
- Bachem: Peptide solubility and handling
End of article
TB-500
for laboratory research
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