TB-500: research reference

The LKKTETQ domain mediates interaction with actin monomers in in vitro studies. This interaction modulates the balance between globular and filamentous actin in cellular models.

The purity value is a product-label specification, not an assay result. A batch result can only be asserted from that batch’s certificate.

These names help identify the catalog entry. A descriptive label is not evidence of efficacy, and structural identity still requires appropriate documentation.

Actin peptide

Reconstitution: Laboratory procedure: allow the closed vial to reach room temperature, disinfect the septum and slowly transfer the diluent against the inner wall of the vial. Do not shake; gently swirl the vial until fully dissolved. Record the volume, diluent and date in the batch log.

Storage: Sealed vial of lyophilized material: store at −20 °C, protected from light and moisture. Avoid repeated freeze-thaw cycles of reconstituted material; aliquot when the experimental design permits.

Personal protective equipment: Handle in a clean work area with a lab coat, nitrile gloves and eye protection. Dispose of vials, tips and sharps according to the laboratory waste procedure.

The catalog identifies TB-500 as full-length thymosin beta-4. However, a 2012 analytical study identified the N-terminally acetylated 17–23 fragment of thymosin beta-4 in a product called TB-500 (PMID 22962027). That finding applies to the product analyzed by the authors, not to Pureza's vial. The fragment and the full-length chain must be distinguished before attributing published findings to the declared ingredient.

The bibliography spans purified-protein biochemistry, mouse thymocytes and three human studies rather than a single model.

At the most basic level, purified-actin experiments in vitro establish direct interaction and preference between molecules without a cell present; they cannot establish tissue behavior. Comparison with the sulfoxide derivative in the same series shows that residue oxidation changes that interaction (PMID 15039539).

The human studies examine different settings. A randomized, double-blind first-in-human phase I study of recombinant human thymosin beta-4 included 54 healthy participants in seven ascending single-exposure cohorts and 30 with repeated exposure, observing safety, tolerability, plasma exposure and antidrug antibodies over 28 days (PMID 34346165). A multicenter, double-masked ophthalmic phase 2 study followed nine participants for 56 days, measuring OSDI questionnaire scores, fluorescein corneal staining, tear-film breakup and tear volume (PMID 25826322). The prospective European dose-escalation study of venous ulcers was planned for 72 participants across ten Italian and Polish sites, with topical application, digital lesion planimetry and plasma peptide measurement (PMID 17495250). A review collects the cellular cascades and studies published by its cutoff (PMID 26096726). Sources: PMID 8055902; PMID 6940133; PMID 34346165; PMID 25826322; PMID 17495250; PMID 26096726.

These sources describe exposure mainly through chemistry. The sulfoxide form accompanies preparations obtained from bovine lung and is attributed to auto-oxidation of methionine at position six. In vitro, the oxidized form retains comparable actin-monomer affinity under nonpolymerizing conditions while showing much less ability to inhibit filament formation (PMID 8055902).

This concerns material handling: the declared sequence places methionine at residue six and contains the sole sulfur atom in C212H350N56O78S. One oxidation site therefore separates species that behave differently in vitro.

Systemic-exposure information here extends little beyond endpoint descriptions. Phase I listed plasma exposure and antidrug antibodies among its measurements (PMID 34346165); this record does not reproduce numerical parameters. These references provide no preclinical half-life, albumin binding or degradation route, and none is estimated here. Sources: PMID 8055902; PMID 34346165.

The molecule was not first characterized as a cytoskeletal regulator. It was isolated from calf thymus and sequenced as a component of thymosin fraction 5: a 43-residue polypeptide with an acetyl-blocked amino terminus, examined through terminal deoxynucleotidyl transferase induction in mouse thymocytes in vivo and in vitro (PMID 6940133). Its first research description was thus a thymic factor associated with lymphocyte maturation. The actin interpretation followed and is established in the later review of cellular cascades and published studies (PMID 26096726).

Two features remain visible in the record. TB-500 is a research designation, while the declared chemical identity is N-terminally acetylated thymosin beta-4 with 43 positions. The LKKTETQ heptapeptide occupies positions 17–23, placing the actin-binding element inside the chain rather than at an end. Sources: PMID 6940133; PMID 26096726.

TB-500 is the catalog’s only actin peptide, so there is no same-class field-by-field comparison. A useful comparison concerns compounds with which it appears in blends.

The declared chain has 43 residues and a mass of 4963.4 Da, compared with fifteen residues and 1419.53 Da for BPC-157, its partner in BPC-157 + TB-500. GHK-Cu and KPV, associated with the Wolverine Complex, GLOW and KLOW blend families, are tripeptides: three residues rather than 43.

The direct actin-monomer interaction measured in vitro using purified protein (PMID 8055902) has no equivalent in the other component records, which describe their own targets. None of these references compares the components with one another; the comparison locates the compound without ranking it. Sources: PMID 8055902.

First, material identity differs: phase I used recombinant human thymosin beta-4 (PMID 34346165), while the catalog declares synthetic acetylated material. None of these references compares those preparations. Second, the European venous-ulcer report describes an ongoing study rather than a completed outcome (PMID 17495250), and the available phase 2 ocular-surface trial enrolled only nine participants (PMID 25826322).

Third, the original thymocyte enzyme-inducing factor description (PMID 6940133) and the later multifunctional repair-peptide description in animal models (PMID 26096726) are not reconciled by a reference in this record. None quantifies the proportion of sulfoxide—functionally different in vitro (PMID 8055902)—in a particular preparation. Sources: PMID 34346165; PMID 17495250; PMID 25826322; PMID 6940133; PMID 26096726; PMID 8055902.