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TB-500 from Epic Peptides Lab is a research-use-only compound supplied in a preloaded 3ml Disposable Self-injection Pen at 5mg/ml for laboratory study, offering consistent measured delivery and reliable handling for researchers.
Epic Peptides Lab · Research Use Only
Thymosin β4 · G-actin sequestration · 3ml at 5mg/ml
The TB-500 Disposable Self-injection Pen is a preloaded 3ml research device containing thymosin β4 in solution at 5mg/ml, giving 15mg of total peptide. Thymosin β4 is a 43-residue peptide, CAS 77591-33-4, molecular weight 4963.55, whose defining property is high-affinity binding to monomeric globular actin.
| Property | Value |
|---|---|
| Device format | Preloaded Disposable Self-injection Pen, glass cartridge |
| Fill volume | 3 ml |
| Concentration | 5 mg/ml |
| Total compound in device | 15 mg |
| Molar concentration | Approximately 1.0 mM |
| Compound | Thymosin β4 |
| Common research name | TB-500 |
| CAS number | 77591-33-4 |
| Molecular formula | C212H350N56O78S |
| Molecular weight | 4963.55 g/mol |
| Residue count | 43 |
| Actin-binding motif | LKKTETQ, residues 17 to 23 |
| Molecular target | Monomeric globular actin (G-actin) |
| Reported action | Sequesters G-actin monomers, holding them out of the polymerising pool |
| Solution structure | Largely unstructured and flexible in free solution |
| Isoelectric point | Approximately 5.1 |
| Reconstitution required | None. Supplied as solution |
| Excipient system | Not published on the product record |
| Solution stability | Not established over device shelf life in published data |
| Storage | 2-8°C, protected from light |
| Purity | Per lot-specific certificate of analysis |
| Regulatory status | No approved human or veterinary formulation in any jurisdiction |
The honest framing is that the compound is a tool for studying actin dynamics, and everything else follows from that.
Actin exists in two interconverting states. Globular actin, G-actin, is the free monomer. Filamentous actin, F-actin, is the polymer built from those monomers. Cells continuously shift the balance between them, and that shifting is what drives cell shape change, migration and division.
Thymosin β4 binds G-actin with high affinity and holds it in the monomeric state. It is the principal G-actin sequestering protein in mammalian cells, present at high intracellular concentration, and its function is to maintain a reservoir of unpolymerised actin available for rapid filament assembly when signalling demands it.
Research applications follow directly. Anything concerning cell migration, cytoskeletal remodelling, or the regulation of the monomer pool can use this peptide as an intervention. Huff and colleagues reviewed the actin biology in detail (Huff et al., International Journal of Biochemistry and Cell Biology, 2001), and Goldstein and colleagues covered the wider research context (Goldstein et al., 2012).
Actin binding localises to a specific seven-residue stretch, LKKTETQ, occupying positions 17 to 23 of the 43-residue sequence. Identifying it was significant because it separated the functional core from the rest of the molecule.
The motif is what physically contacts actin, and synthetic peptides consisting of the motif alone retain measurable actin-binding activity. That has practical consequences for anyone comparing preparations, because fragments containing only this region have been sold under the TB-500 name historically, and they are not the same molecule as the full 43-residue peptide.
The distinction matters for interpretation. A fragment binds actin, but it lacks whatever contribution the remaining 36 residues make to binding kinetics, cellular uptake and stability. Findings generated with one should not be assumed to transfer to the other.
For a preparation like this one, confirm from the certificate of analysis that the material is full-length thymosin β4 at 4963.55 daltons rather than a motif-containing fragment. The mass difference is large enough that no ambiguity should survive a mass spectrometry check.
Thymosin β4 is intrinsically disordered in free solution. It adopts no stable fold, existing instead as a flexible chain sampling many conformations, and it becomes ordered only on binding actin.
That behaviour has real analytical consequences. Circular dichroism, which reports secondary structure content, gives a spectrum characteristic of a random coil rather than the defined helix or sheet signatures used to confirm folding in structured proteins. A disordered spectrum is the correct finding here, not evidence of denaturation.
Size-exclusion chromatography also behaves unexpectedly. A disordered chain occupies a larger hydrodynamic volume than a folded protein of the same mass, so the peptide elutes earlier than its molecular weight would predict. Calibrating against globular standards and reading the answer literally will overestimate the mass.
The practical upshot is that standard protein characterisation methods need interpreting differently for this molecule, and a finding that looks anomalous against globular-protein expectations may be entirely normal.
Device-oriented queries dominate the demand reaching the TB-500 Disposable Self-injection Pen page, which says the audience is evaluating format as much as compound.
A preloaded pen removes the reconstitution step and the variability it introduces. For a 43-residue peptide that variability is not trivial: incomplete dissolution of a large lyophilized cake, shear from over-agitation, adsorptive loss during transfer, and inconsistent time between reconstitution and use all affect delivered concentration invisibly.
Against that, solution-state supply means the peptide has been in aqueous conditions since manufacture. For an intrinsically disordered peptide, aggregation is the principal concern, since disordered chains have exposed hydrophobic surface that a folded protein would bury. Aggregated material is inactive and can interfere with the assay it enters.
At 5 mg/ml the solution is approximately 1.0 millimolar, which is a convenient starting point for most cell-based work and requires fewer dilution steps than the picomolar arithmetic some peptides in this catalogue demand.
Gravimetric checking of the TB-500 Disposable Self-injection Pen is the direct method and takes minutes. Actuate onto a tared weighing vessel, record delivered mass, convert through solution density, and repeat across several actuations to capture accuracy against nominal volume and precision between draws.
Perform the check at the temperature of intended use rather than straight from refrigeration, since cold solution is more viscous and viscosity affects delivery in a spring-driven mechanism.
Inspect the solution before each draw, against both light and dark backgrounds. Aggregation in a disordered peptide frequently appears first as faint opalescence rather than obvious turbidity, and a dark background makes that early stage visible when a light one will not.
Treat the first actuation after a rest period as suspect. Air ingress into the delivery path and seal relaxation both cause under-delivery on first use, and unless a priming step is specified and followed, the first draw should not be trusted until gravimetric data says otherwise.
Several established methods report on the G-actin sequestration the TB-500 Disposable Self-injection Pen is used to study, and they answer subtly different questions.
The pyrene-actin polymerisation assay is the workhorse. Actin labelled with pyrene at cysteine 374 shows a large fluorescence increase on incorporation into filaments, so polymerisation can be followed in real time. A sequestering agent reduces the rate and the plateau, and the concentration dependence of that reduction gives an apparent affinity.
The critical concentration assay measures the same underlying property differently. At steady state, free monomer concentration sits at a fixed value determined by filament thermodynamics. A sequestering protein raises the apparent critical concentration, because some monomer is held unavailable, and the shift quantifies how much.
Direct binding measurement by isothermal titration calorimetry or surface plasmon resonance gives the affinity without inferring it from polymerisation behaviour. These are more demanding and more definitive.
One methodological caution applies across all of them. Thymosin β4 binds ATP-actin considerably more tightly than ADP-actin, so nucleotide state changes the measured affinity. An assay that does not control the nucleotide state is measuring an average across whatever mixture happens to be present, which is why published affinity values vary more than they should.
Thymosin beta 4 sits at an awkward size for peptide chemistry, long enough to raise synthesis difficulty and short enough that recombinant expression is often not worth the setup.
Solid-phase synthesis efficiency compounds across couplings. Even at 99.5 percent per step, a 43-residue chain accumulates measurable deletion sequences, and those deletion products differ from the target by a single residue, which makes them hard to resolve chromatographically.
That has a direct implication for purity interpretation. A 98 percent purity figure on a 43-residue peptide means something different from the same figure on a tripeptide, because the impurity profile of the longer peptide is dominated by closely related sequences rather than by unrelated material.
For actin-binding work the practical question is whether deletion products retain activity. A sequence missing a residue outside the LKKTETQ motif may bind normally, while one missing a residue inside it may not, and a bulk purity figure cannot distinguish those cases.
Where the work depends on precise stoichiometry, mass spectrometry showing the impurity distribution is more informative than a single purity percentage.
Store at 2-8°C protected from light, returning the device to its packaging between sessions rather than leaving it out on a bench.
Record device lot number, date of first actuation, storage conditions and volume drawn at each session. Because solution-state stability over shelf life is not published for this format, the interval between first use and each later draw is an experimental variable that belongs in the record.
Where the solution enters a downstream actin assay, remember that the peptide is being added to a system whose entire readout concerns the monomer-polymer balance. Vehicle controls matter more than usual, because excipients in an unpublished formulation could themselves affect actin dynamics, and nobody has ruled that out for this product.
Confirmed against publisher records or primary indexes before inclusion. The entries cover actin biology rather than this device format, which has no published data behind it.
What is the TB-500 Disposable Self-injection Pen?
A preloaded 3ml research device containing thymosin beta 4 in solution at 5mg/ml, giving 15mg total, approximately 1.0 millimolar. CAS 77591-33-4, molecular weight 4963.55, 43 residues. Research use only in a laboratory setting. No approved formulation exists for humans or animals.
What is TB-500 used for in research?
Studying actin dynamics. Thymosin beta 4 binds monomeric globular actin with high affinity and holds it out of the polymerising pool, making it the principal G-actin sequestering protein in mammalian cells. Applications cover cell migration, cytoskeletal remodelling and regulation of the monomer pool.
What is the LKKTETQ motif?
The seven-residue actin-binding stretch at positions 17 to 23 of the 43-residue sequence. It is the region that physically contacts actin, and synthetic peptides consisting of the motif alone retain measurable binding activity, which is why fragments have historically been sold under the TB-500 name.
Is TB-500 the same as thymosin beta 4?
In current usage generally yes, referring to the full 43-residue peptide at 4963.55 daltons. Historically the name has also been applied to motif-containing fragments, which are not the same molecule. The mass difference is large enough that a mass spectrometry check removes any ambiguity.
Why does intrinsic disorder complicate analysis?
Because standard protein methods assume a folded structure. Circular dichroism returns a random-coil spectrum, which is correct here rather than evidence of denaturation. Size-exclusion chromatography elutes the peptide earlier than its mass predicts, since a disordered chain occupies a larger hydrodynamic volume than a folded protein.
What concentration does the device deliver?
Five milligrams per millilitre, approximately 1.0 millimolar. That is a convenient starting point for most cell-based work and requires fewer serial dilution steps than compounds active in the picomolar range, where accumulated pipetting error becomes a real concern.
What is the main risk with solution-state supply?
Aggregation. An intrinsically disordered peptide has exposed hydrophobic surface that a folded protein would bury, which makes association more likely in solution than in a lyophilized cake. Aggregated material is inactive and can interfere with the assay it enters.
How should the device be verified?
Gravimetrically. Actuate onto a tared vessel, record delivered mass, convert using solution density, repeat across several actuations. Run the check at the temperature of intended use, and treat the first actuation after a rest period as suspect until data establishes otherwise.
What should be inspected before each draw?
The solution, against both light and dark backgrounds. Aggregation in a disordered peptide typically appears first as faint opalescence rather than obvious turbidity, and a dark background makes that early stage visible when a light background will not.
Why do vehicle controls matter more here?
Because the downstream readout usually concerns the actin monomer-polymer balance, and the excipient system in this device is not published. Excipients could themselves affect actin dynamics, and nobody has ruled that out for this formulation, so a matched vehicle arm is not optional.
How is actin binding measured?
Most commonly by pyrene-actin polymerisation assay, where actin labelled at cysteine 374 shows a large fluorescence increase on filament incorporation, so a sequestering agent reduces both rate and plateau. Critical concentration assays and direct binding by calorimetry or surface plasmon resonance are the alternatives.
Why do published affinity values vary?
Largely because of nucleotide state. Thymosin beta 4 binds ATP-actin considerably more tightly than ADP-actin, so an assay that does not control which form is present measures an average across whatever mixture exists. Controlling nucleotide state narrows the spread considerably.
What does the critical concentration assay add?
It measures the same property from a different direction. At steady state, free monomer concentration sits at a value set by filament thermodynamics. A sequestering protein raises the apparent critical concentration because some monomer is held unavailable, and the size of that shift quantifies the sequestration.
The TB-500 Disposable Self-injection Pen is sold exclusively for laboratory research use. It is not a drug, food, or cosmetic product, and it is not a dietary product of any kind. It is not approved by the FDA or any comparable authority for human or veterinary use. This product is not intended to diagnose, treat, cure, or prevent any disease. It must not be given to humans or animals. Purchase is restricted to qualified researchers and institutions operating within applicable laws. All handling is the responsibility of the purchasing laboratory.
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