> For Research Use Only (RUO). TB-500 Fragment 17-23 is not approved by the FDA for human use. All information on this page is intended solely for licensed researchers conducting preclinical investigations in controlled laboratory settings.
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What Is TB-500 Fragment 17-23?
TB-500 Fragment 17-23 — also written as TB-500 Frag, TB500 Fragment, or simply the LKKTETQ heptapeptide — is a synthetic seven-amino-acid peptide corresponding to residues 17 through 23 of Thymosin Beta-4 (Tβ4), a naturally occurring 43-amino-acid protein found throughout mammalian tissue.
The full sequence of this fragment is Ac-LKKTETQ (Leucine–Lysine–Lysine–Threonine–Glutamic Acid–Threonine–Glutamine), with an N-terminal acetyl group added for metabolic stability. At approximately 843–889 Da, it is roughly one-sixth the molecular weight of the complete Thymosin Beta-4 molecule (4,921 Da).
This stretch of seven amino acids represents the functional actin-binding domain of Thymosin Beta-4. Structural biologists identified this core motif in the early 2000s by mapping which sub-sequences of Tβ4 were necessary and sufficient to bind monomeric (G-)actin — the building block of actin filaments that govern cell shape, migration, and cytoskeletal dynamics.
The LKKTETQ Actin-Binding Motif
The actin-binding site within residues 17–23 is conserved across all beta-thymosin family members and shares homology with WH2 (Wiskott-Aldrich Homology 2) domains found in a wide range of actin-regulatory proteins.
Structurally, the two lysine residues (positions 2 and 3 of the fragment, corresponding to K18 and K19 of full Tβ4) form electrostatic interactions with negatively charged surfaces on actin subdomains 1 and 4. The threonine residues contribute polar contacts, while the glutamine at the C-terminus stabilizes the bound conformation. Together, these contacts enable the fragment to sequester monomeric actin, preventing its incorporation into polymerized actin filaments (F-actin) — a process central to cell migration, wound repair, and tissue remodeling.
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How TB-500 Fragment 17-23 Differs from Full TB-500 (Thymosin Beta-4)
Understanding the distinction between the full Thymosin Beta-4 peptide and its 17-23 fragment is essential for designing sound research protocols. The two are related but not pharmacologically equivalent.
| Property | TB-500 Fragment 17-23 | Full TB-500 (Thymosin Beta-4) |
|---|---|---|
| Sequence | Ac-LKKTETQ (7 amino acids) | Full 43-amino-acid sequence |
| Molecular weight | ~843–889 Da | ~4,921 Da |
| Actin binding | Yes (primary domain) | Yes (same domain + full context) |
| Anti-inflammatory domain (Ac-SDKP) | No | Yes (residues 1–4) |
| Anti-apoptotic domain | No | Yes (residues 1–15) |
| Hair growth activity | Limited evidence | Reported in full peptide |
| Research evidence base | Limited direct studies | Extensive (most TB-4 research) |
| Cost per mg | Generally lower | Higher per equivalent dose |
| Synthesis complexity | Simpler, shorter peptide | More complex manufacturing |
What the Fragment Retains
The LKKTETQ core retains the primary actin-sequestering activity of the full peptide. Laboratory studies confirm it can:
- •Bind monomeric G-actin at the same interface as Tβ4
- •Inhibit actin polymerization (F-actin formation)
- •Stimulate keratinocyte migration in cell culture models
- •Contribute to angiogenesis and wound-healing signaling at the cellular level
What the Fragment Lacks
The 17-23 fragment does not carry the N-terminal Ac-SDKP sequence (residues 1–4) that underlies Tβ4's anti-inflammatory and anti-fibrotic activity — a domain that has been investigated in separate research on fibrosis and organ protection. It also lacks the C-terminal regions associated with cardiac progenitor cell activation, which have been studied in landmark Nature papers using full-length Tβ4 in epicardial regeneration models.
A Critical 2024 Finding on Wound Healing
A 2024 study published in the Journal of Pharmaceutical and Biomedical Analysis added an important nuance to how researchers interpret fragment 17-23 activity: the paper found that the fragment itself (Ac-LKKTETQ) did not significantly enhance wound healing in its tested model, but its metabolite Ac-LKKTE did. This suggests that some reported wound-healing activity attributed to TB-500 may be driven by metabolic breakdown products rather than the parent heptapeptide itself — a finding that has implications for how in vitro vs. in vivo results should be interpreted. As of 2025, this remains an active area of investigation.
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Why Researchers Choose the Fragment Over Full TB-500
Several practical and scientific considerations motivate the use of TB-500 Fragment 17-23 over the full-length peptide in research settings:
Structure-Activity Relationship (SAR) Studies
The fragment allows researchers to isolate the actin-binding mechanism from Tβ4's broader biological activity. When studying actin dynamics specifically, using the minimal functional domain avoids confounding from anti-inflammatory, anti-apoptotic, or cardiac-progenitor-activating pathways present in the full molecule.
Lower Cost and Simpler Synthesis
At roughly one-sixth the molecular weight, Fragment 17-23 is significantly cheaper to synthesize than full-length Thymosin Beta-4. This cost advantage makes it attractive for high-throughput in vitro studies requiring milligram-scale quantities.
Comparative Pharmacology
Fragment 17-23 serves as a reference compound for understanding the minimum sequence requirements for β-thymosin biological activity, supporting the development of next-generation actin-binding peptides and peptidomimetics.
Metabolic Stability
The N-terminal acetyl group confers resistance to aminopeptidase degradation, giving the fragment reasonable stability in biological matrices compared to non-acetylated peptide sequences.
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Reconstitution Protocol for TB-500 Fragment 17-23
> Laboratory use only. The following protocol is adapted from standard research peptide reconstitution practices. This is not a clinical or dosing recommendation.
Materials Needed
- •Lyophilized TB-500 Fragment 17-23 vial (typically 5 mg or 10 mg)
- •Bacteriostatic water (preferred) or sterile water for injection
- •Sterile syringes and needles
- •Alcohol swabs
Reconstitution Steps
| Step | Action |
|---|---|
| 1 | Allow the vial to reach room temperature before opening (prevents condensation contamination) |
| 2 | Wipe the vial septum with an alcohol swab; let dry |
| 3 | Draw the appropriate volume of bacteriostatic water into a syringe |
| 4 | Inject the water slowly along the inside wall of the vial — do not inject directly onto the powder |
| 5 | Gently swirl (do not shake) until the powder dissolves completely |
| 6 | Inspect for clarity — the solution should be colorless and clear |
| 7 | Label the vial with date and concentration |
Standard Concentration Calculation
A common research dilution is 2 mL bacteriostatic water per 5 mg vial, yielding a working concentration of 2.5 mg/mL (2,500 mcg/mL).
For a 10 mg vial reconstituted in 2 mL: 5 mg/mL (5,000 mcg/mL).
Storage After Reconstitution
- •Refrigerate at 2–8°C; use within 28 days
- •Do not freeze reconstituted peptide
- •Dry lyophilized powder: Store at -20°C until use; avoid repeated freeze-thaw cycles
- •Protect from light; use amber vials or foil wrapping where possible
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Research Dosing: How Literature Compares Fragment to Full TB-500
Because no human clinical trials exist for TB-500 Fragment 17-23, all research dosing extrapolates from two sources:
1. Full-length Thymosin Beta-4 animal and phase I human studies (Ruff et al., 2010; Malinda et al., 1999)
2. Community research protocols adapted for the molecular weight difference
Molecular Weight Adjustment
Full TB-4 is approximately 5.5× heavier than Fragment 17-23. When comparing molar concentrations, a given mass of Fragment 17-23 represents far more moles of peptide than the same mass of full Tβ4. In practice, most research protocols do not apply molar equivalence corrections — they use similar absolute mass doses (in mg) and observe functional outcomes.
Common Research Dosing Ranges Reported in Literature
| Protocol Phase | Reported Research Dose (Fragment 17-23) | Frequency |
|---|---|---|
| Loading phase | 2–5 mg per administration | 2× per week for 4–6 weeks |
| Maintenance phase | 1–2 mg per administration | 1× per week |
| Acute tissue study | 1–10 mg/kg (rodent in vivo) | Variable per study design |
> Important: These are observed ranges from preclinical research literature and research community data aggregation — not clinical recommendations. Dose selection in any research setting must follow IACUC-approved protocols and institutional guidelines.
Estimated Half-Life
Based on animal pharmacokinetic data for the parent Thymosin Beta-4 molecule, TB-500 Fragment 17-23 is estimated to have a plasma half-life of approximately 48–72 hours. This longer half-life (relative to short peptides like BPC-157) supports dosing schedules of every 3–4 days in many research designs.
Tissue-level effects may persist beyond plasma clearance, a property observed with full-length Tβ4 in wound model studies.
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Key Research Areas: Wound Healing, Angiogenesis, and Inflammation
Wound Healing
The foundational wound-healing evidence for the Tβ4 LKKTETQ motif comes from Malinda et al. (1999, Journal of Investigative Dermatology), which demonstrated in a rat full-thickness dermal wound model that Tβ4 increased wound reepithelialization by 42% over saline controls at day 4, and up to 61% at day 7. Both topical and intraperitoneal administration were effective.
Subsequent research confirmed that Thymosin Beta-4 — and by mechanistic extension, its actin-binding fragment — stimulates keratinocyte migration, accelerates re-epithelialization, and promotes collagen deposition in the wound bed.
Multiple active domains of Tβ4 have been mapped: residues 1–4 for anti-inflammatory activity, 1–15 for anti-apoptotic and cytoprotective effects, and 17–23 specifically for cell migration, actin binding, dermal wound healing, angiogenesis, and hair growth — establishing Fragment 17-23 as the primary tissue-repair domain.
Angiogenesis
Thymosin Beta-4 has been recognized as a pro-angiogenic peptide since the late 1990s, when it was found to be highly concentrated in platelets (which release growth factors at sites of injury). In the first full-thickness dermal wound studies, Tβ4 accelerated new blood vessel formation alongside wound closure and collagen deposition.
The pro-angiogenic effect is mechanistically linked to the LKKTETQ domain's ability to promote endothelial cell migration — the same G-actin sequestration and cytoskeletal remodeling that drives keratinocyte migration also underlies endothelial tube formation and capillary sprouting.
Research has also investigated Tβ4's role in cardiac angiogenesis, corneal repair (RGN-259 clinical program), and peripheral neuropathy models — though most of this work uses full-length peptide rather than Fragment 17-23 directly.
Inflammation
While the primary anti-inflammatory domain of Tβ4 resides in residues 1–4 (the Ac-SDKP motif, which inhibits NF-κB signaling), the LKKTETQ fragment contributes indirectly to inflammation resolution by promoting tissue repair and re-epithelialization — processes that reduce chronic inflammatory signaling at wound sites.
Researchers investigating inflammation-driven tissue damage (e.g., in models of musculoskeletal injury or inflammatory bowel disease) typically prefer full-length Tβ4 to capture the complete anti-inflammatory profile, while Fragment 17-23 is used when the goal is specifically to isolate actin dynamics and cell migration mechanisms.
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Storage and Stability
| Form | Storage Temperature | Stability |
|---|---|---|
| Lyophilized powder (sealed) | -20°C | 12–24 months |
| Lyophilized powder (room temp) | 15–25°C | Up to 3 months (short-term) |
| Reconstituted solution | 2–8°C | 28 days |
| Reconstituted solution | -20°C | Not recommended (freeze-thaw degrades peptide) |
Lyophilized TB-500 Fragment 17-23 is relatively stable due to its short sequence and acetylated N-terminus. Avoid repeated freeze-thaw of the dry powder. Once reconstituted, the peptide should be handled as a biological reagent: refrigerate, protect from light, and use within the labeled period.
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Cost Comparison: Fragment 17-23 vs. Full TB-500
One of the primary practical drivers for using Fragment 17-23 in research is cost. Because the peptide is shorter and simpler to synthesize, it commands a significantly lower price per milligram on the research market.
| Product | Typical Research Market Price | Notes |
|---|---|---|
| TB-500 Fragment 17-23 (5 mg) | $15–$35 | Most common research vial size |
| TB-500 Fragment 17-23 (10 mg) | $25–$55 | Better per-mg economy |
| Full TB-500 / Thymosin Beta-4 (5 mg) | $40–$90 | Full 43-AA sequence |
| Full TB-500 / Thymosin Beta-4 (10 mg) | $75–$160 | Higher synthesis cost |
> Prices represent observed ranges across research peptide suppliers as of 2025–2026. Pricing varies by vendor, purity certification, and regional availability.
The cost delta makes Fragment 17-23 particularly attractive for high-volume preclinical screening, cell culture assays, and dose-response studies where multiple treatment conditions are run in parallel.
Purity Standards to Look For
Research-grade TB-500 Fragment 17-23 should meet the following specifications for reliable experimental results:
- •Purity: ≥98% (HPLC), ideally ≥99%
- •Identity confirmation: Mass spectrometry (LC-MS or MALDI-TOF)
- •Third-party testing: Certificates from independent labs (e.g., Janoshik Analytical, MZ Biolabs, Colmaric Analyticals)
- •Endotoxin testing: Required for cell culture applications
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Related Research Articles
- •TB-500 (Thymosin Beta-4) Research Guide — Comprehensive overview of the full parent peptide, its mechanism of action, and research protocols
- •BPC-157 vs TB-500: Regenerative Peptide Comparison — How these two commonly studied repair peptides differ in mechanism, evidence base, and research applications
- •Peptide Reconstitution Calculator — Calculate exact volumes and concentrations for any peptide vial
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Disclaimer
> For Research Use Only (RUO). TB-500 Fragment 17-23 (Ac-LKKTETQ) is not approved by the U.S. Food and Drug Administration (FDA) or any equivalent regulatory body for human or veterinary clinical use. It is not a drug, dietary supplement, food, or cosmetic. All research involving this compound must comply with applicable institutional, local, state, and federal regulations. This article is for educational and scientific reference purposes only and does not constitute medical advice, a clinical recommendation, or an endorsement of any commercial product.