Also known as: TB-500 Frag 17-23, TB4 17-23, LKKTETQ, Actin-Binding Domain Fragment
Half-life: Estimated minutes to a few hours (much shorter than full TB-500 due to lack of N/C-terminal protection)
Last reviewed: · Published:
TB-500 Fragment 17-23 is a heptapeptide (sequence LKKTETQ) corresponding to amino acids 17–23 of Thymosin Beta-4 — the segment that contains the actin-binding domain widely considered responsible for the parent molecule's wound-healing and cell-migration activity. Isolating this active region rather than synthesizing the full 43-residue Thymosin Beta-4 was originally a research convenience: the fragment is dramatically cheaper to manufacture and easier to handle, while preliminary in vitro work suggested it retains a meaningful share of the actin-binding behavior.
Mechanistically, the fragment binds G-actin and is thought to modulate actin polymerization in migrating cells — the same process implicated in keratinocyte migration during wound closure, endothelial cell migration during angiogenesis, and stem cell recruitment to injured tissue. Whether the isolated fragment recapitulates the full systemic activity of TB-500 in vivo is still an open question, but in vitro and limited preclinical studies have shown some shared activities, particularly for local wound healing applications.
Because Fragment 17-23 lacks the additional binding sites and structural context of the full Thymosin Beta-4 molecule, it has a much shorter half-life and likely needs more frequent dosing or higher local concentrations than the parent peptide. Research peptide community use is largely extrapolated from full TB-500 dosing — there is no human pharmacokinetic data to anchor protocols.
The LKKTETQ active-site sequence was identified in the late 1990s and early 2000s during structural studies of Thymosin Beta-4 by Ho et al. and the Goldstein lab, who showed that the actin-binding capability of the full molecule mapped largely to this central region. Subsequent in vitro work demonstrated that the isolated fragment retained partial activity in promoting endothelial cell migration and angiogenesis assays, leading to speculation that it could serve as a more economical research tool than the full Thymosin Beta-4.
The fragment entered the research peptide community in the 2010s as vendors began offering it as a lower-cost alternative to full TB-500, marketing it on the basis of shared mechanism. Unlike full TB-500, Fragment 17-23 has not been the subject of formal clinical trials and remains a research-only compound with limited published efficacy data in vivo.
No formal clinical safety data exists for TB-500 Fragment 17-23 in humans. Anecdotal reports from the research peptide community suggest similar tolerability to full TB-500 — generally well tolerated at typical research doses, with injection site reactions and occasional lethargy being the most reported issues. Because the fragment is much smaller than the parent molecule, immunogenicity is theoretically lower, but there is no clinical evidence either way. The compound should be treated as fully experimental.
Dose Range
2-5 mg
Frequency
Twice weekly SubQ
Duration
4-6 weeks
Dose Range
2-5 mg
Frequency
Twice weekly SubQ
Duration
4-8 weeks
Dose Range
5 mg
Frequency
Twice weekly for 2-3 weeks
Duration
Then maintenance
Dosing information is for educational purposes only. Consult a healthcare professional before using any peptide.
Typical Vial Size
10 mg
Water Type
Bacteriostatic water (BAC water)
Mixing Volume
2 mL
Half-Life
Estimated minutes to a few hours (much shorter than full TB-500 due to lack of N/C-terminal protection)
Molecular Weight
861.0 Da
Reconstitute a 10mg vial with 2mL of BAC water for a 5 mg/mL concentration. Store refrigerated at 2-8°C and use within 28 days. The shorter peptide may be slightly more stable than full TB-500 but should still be protected from light, heat, and freeze-thaw cycles.
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FDA Status
Not FDA approved for any human or veterinary use. No clinical trials have been conducted on this specific fragment.
Legal Status
Unregulated research chemical. Prohibited by WADA as part of the broader Thymosin Beta-4 / TB-500 ban on growth factors.
USA
Not approvedResearch chemical only — no clinical trials registered
EU
Not approvedNot authorized as medicinal product
UK
Not approvedClassified as research chemical
Australia
Not approvedTGA has not evaluated
Canada
Not approvedHealth Canada has not authorized
Sosne G, Qiu P, Christopherson PL, Wheater MK
The FASEB Journal (2007)
Demonstrated that the central LKKTETQ heptapeptide sequence (Fragment 17-23) recapitulates a substantial portion of Thymosin Beta-4's wound-healing activity in corneal injury models, supporting the rationale for the fragment as a standalone research tool.
View Study →Philp D, Goldstein AL, Kleinman HK
Wound Repair and Regeneration (2004)
Compared full Thymosin Beta-4 with a synthetic peptide containing the actin-binding domain in diabetic mouse wound models; the fragment retained much of the wound-healing activity of the full molecule.
View Study →Malinda KM, Sidhu GS, Mani H, Banaudha K, Maheshwari RK, Goldstein AL, Kleinman HK
Journal of Investigative Dermatology (1999)
Foundational paper showing Thymosin Beta-4 promotes endothelial cell migration and angiogenesis — work that later motivated identification of the active fragment as the responsible region.
View Study →Synthetic fragment of Thymosin Beta-4 with potent tissue repair activity.
Gastric pentadecapeptide with broad tissue-healing properties.
Copper-binding tripeptide with potent wound-healing, skin-remodeling, and gene-regulatory properties.
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