ABP-7 / TB-500 Fragment 17-23 (Ac-LKKTETQ)

1 Identity

Synthetic N-acetylated heptapeptide fragment of an endogenous protein. "thymosin beta-4" or "TB4". "ABP-7" is a separate trade name whose identity the source material could not resolve to a defined molecule and is not treated here as a synonym. sold and routinely mislabeled simply as "TB-500".

Sequence

Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH; one-letter Ac-LKKTETQ-OH. Seven residues, all L-proteinogenic. The N-terminal acetyl sits on the leucine alpha-amino nitrogen and is part of the molecule, not a protecting group left in place, and it is localized by MS/MS rather than inferred from intact mass. The C-terminus is the free acid of glutamine, not an amide. No cysteine, no disulfide, no D-residue and no non-proteinogenic residue — stated explicitly so that P3 is not applied by reflex. This is residues 17 to 23 of thymosin beta-4: a fragment, and not the parent protein. Separately and importantly: no sequence is asserted for "ABP-7".

Molecular formula

C38H68N10O14 (free base, C-terminal free acid). Applies to Ac-LKKTETQ only; no formula is stated for "ABP-7".

Average mass

889.018 Da (C38H68N10O14), from the formula with IUPAC 2021 conventional atomic weights. The cataloged value of 889.0 (PubChem CID 62707662) is consistent with it.

Monoisotopic mass

888.4917 Da. [M+H]+ 889.4989; [M+2H]2+ 445.2531; [M-H]- 887.4844.

Salt / variant note

(1) the parent protein, which is not this molecule. Full-length thymosin beta-4, 43 residues, Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES-OH, C212H350N56O78S, 4963.51 average / 4960.4863 monoisotopic — 5.58 times the mass of the fragment. FDA names the two separately. Every human result published under the "thymosin beta-4" name belongs to the parent. (2) the isobaric trap, and it is inside this same catalog. Acetyl hexapeptide-8, Ac-EEMQRR-NH2, C34H60N14O12S, 889.00 average / 888.4236 monoisotopic. The two average masses differ by 0.02 Da, which no average-mass tolerance stated in this channel can resolve; the monoisotopic masses differ by 0.0681 Da, which is 77 ppm at m/z 889 — trivially resolvable by HRMS at a 10 ppm tolerance and completely invisible at unit resolution. Different sequence, different length, different terminus chemistry, one of them contains sulfur and the other does not, and they are sold in the same catalogs at similar per-milligram prices. Any certificate for either that reports only an average mass near 889 has excluded neither. (3) Ac-LKKTE, the downstream metabolite. A 2024 in-vitro and rat metabolic study (Rahaman 2024) attributes the response its fibroblast assay recorded to this metabolite rather than to the administered heptapeptide, which is why the identity of the species actually under study is contested in the primary literature — a chemistry problem before it is anything else: C29H53N7O10, 659.78 average / 659.3854 monoisotopic, 229.24 Da lighter. (4) Des-acetyl H-LKKTETQ-OH, C36H66N10O13, 846.98 average / 846.4811 monoisotopic — 42.04 Da lighter, and the direct process residue when the acetylation step is incomplete. (5) The C-terminal amide Ac-LKKTETQ-NH2, C38H69N11O13, 888.03 average / 887.5076 monoisotopic — 0.98 Da lighter than the free acid and therefore inside any tolerance stated in whole daltons. (6) "ABP-7" as sold: no formula, no mass, no sequence and no structure declaration obtainable; one catalog listing found at 10 mg.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists and is in vitro, rodent and equine; no registered or published human clinical trial of this molecule has been identified. Chemical synthesis and analytical characterization: Esposito S et al., Drug Test Anal 2012, PMID 22962027, DOI 10.1002/dta.1402. Equine disposition and doping-control analysis: Ho EN et al., J Chromatogr A 2012, PMID 23084823, DOI 10.1016/j.chroma.2012.09.043; Kwok WH et al., Anal Bioanal Chem 2013, PMID 23318763, DOI 10.1007/s00216-012-6697-9. In vitro plus mouse: Huang CM et al., Proteomics 2006, PMID 17001601, DOI 10.1002/pmic.200600163; Lu P et al., ACS Appl Mater Interfaces 2025, PMID 41359360, DOI 10.1021/acsami.5c14652. In-vitro and rat metabolite-attribution study addressing whether the administered heptapeptide or its downstream metabolite Ac-LKKTE is the species to which the response recorded in its fibroblast assay should be attributed: Rahaman 2024. Reviews: Sosne 2010, FASEB J, DOI 10.1096/fj.09-142307; Gomez-Guerrero NA et al., ACS Omega 2022, PMID 36340120, DOI 10.1021/acsomega.2c05296; Mavrych V et al., Front Aging 2026, PMID 42021992, DOI 10.3389/fragi.2026.1790247. Human trials published under the "thymosin beta-4" name (RGN-259; NCT03937882) used the 43-residue parent as a topical formulation and belong to that record, not this one. No published literature of any kind was identified under the name "ABP-7".

4 Storage & specification

Storage

Lyophilized solid in a Type I amber glass vial with nitrogen-flushed headspace, elastomeric stopper and aluminum crimp seal. Labeled: store at -20 degrees C plus or minus 5 degrees C, protect from light and moisture, equilibrate the sealed vial to room temperature before opening to prevent condensation onto the cake. The article is hygroscopic — a lysine-bearing peptide salt takes up water quickly in open air — so Karl Fischer runs at release and at every retest point and the label carries a close-immediately-after-weighing instruction. Reconstituted solution is aliquoted single-use and held at -80 degrees C; it is never refrozen, because the published concern on this substance is aggregation and freeze-thaw is the cheapest way to create it. Ships ambient with a labeled cumulative excursion allowance of 120 hours at or below 30 degrees C on the shipping record; gel packs at 2-8 degrees C beyond that; single-use temperature logger in every export carton.

Shelf life

Shelf life is provisional at 24 months at -20 degrees C plus or minus 5 degrees C from the date of QA release, pending the company's own stability data, with aggregate content by SE-HPLC, total related substances and Karl Fischer water as the stability-indicating attributes. Extension to 36 months only on real-time data at 12, 18, 24 and 36 months supported by accelerated data at 40 degrees C / 75% RH at 1, 3 and 6 months. Printed retest date on every vial and first-expiry-first-out enforced against that date, not against receipt date.