Thymosin Alpha-1 (Ta1)

1 Identity

Base synthetic peptide, 28 residues, all-L, no disulfides, carrying exactly one defining covalent modification: N-alpha-acetylation of Ser1. The sequence is identical to the native human peptide, so the synthetic article is a replicate rather than an analog. Strongly acidic, with ten Asp/Glu against four Lys, which governs its chromatographic behavior and makes counterion and net-peptide determination unavoidable. No Trp, Tyr or Phe anywhere in the chain, so the molecule has no 280 nm chromophore at all. Supplied as the lyophilized free base or acetate salt. CAS 62304-98-7. Corresponds to UniProt P06454 (prothymosin alpha, PTMA) residues 2-29.

Sequence

Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH. One-letter: Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN-OH. Twenty-eight residues, all-L, no disulfides. Both termini belong on the certificate: N-alpha-acetylation of Ser1, the single defining covalent modification, and a free acid at Asn28. One caution attaches to the string itself: sequence strings for this peptide taken from secondary sources have shown at least one single-residue transcription error, so the authoritative checkable form is the accession and residue range, UniProt P06454 residues 2-29, and anyone reproducing the string for synthesis should read it from UniProt directly rather than from a secondary source.

Molecular formula

C129H215N33O55 (free base). Mono-acetate salt C131H219N33O57. Des-acetyl species, the specific failure mode of this synthesis, C127H213N33O54.

Average mass

Average mass 3108.315 Da (C129H215N33O55, free base), computed from the formula. Published figures for the same formula are 3108.28 (NCI/CADD resolver) and 3108.3 (a reagent supplier's catalog entry); both sit on the older atomic-weight table, and at 3.1 kDa the 0.035 Da spread is 11 ppm and is a table difference rather than a discrepancy of substance. Mono-acetate salt 3168.367 Da. Des-acetyl 3066.278 Da, exactly 42.037 Da lighter.

Monoisotopic mass

3106.50413 Da neutral (C129H215N33O55); [M+H]+ 3107.51140. At this mass the measurement that matters is the deconvoluted multiply-charged envelope, reported as a charge-state series with the deconvoluted neutral stated to four decimals. Des-acetyl 3064.49356. Asn28 deamidation is plus 0.984 Da (3109.299 average, 3107.48814 monoisotopic) and does not change chain length, so it is invisible below roughly 30,000 resolving power and invisible to any nominal-mass method.

Salt / variant note

The specific failure mode of this synthesis: des-acetyl Ta1, capping step skipped or partial, C127H213N33O54, 3066.278 / 3064.49356, exactly 42.037 Da lighter, same 28 residues, same retention window. This is the substitution that an identity statement reading "consistent with a 28-residue peptide" passes without comment, and it is the single most likely thing in a substandard vial. Salt form as A commercial variable: mono-acetate C131H219N33O57, 3168.367, and the trade sells the two forms as separate SKUs at very different prices, one supplier carrying the free base and the acetate under separate catalog numbers, so free base versus acetate is a live distinction under one name. Arithmetic trap rather than substitution: Asn28 deamidation, plus 0.984 Da, 3109.299 / 3107.48814, no change in chain length. A C-terminal amide instead of the specified free acid is minus 0.984 Da, 3107.331 / 3105.52011, the same magnitude in the other direction. Different molecules in the naming cluster, each of which has been shipped against a "thymosin" order: thymosin beta-4, Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES-OH, C212H350N56O78S, 4963.506 / 4960.48632; TB-500, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, C38H68N10O14, 889.018 / 888.49165, the cheapest article in the cluster and the one most often substituted; thymopentin, H-Arg-Lys-Asp-Val-Tyr-OH, C30H49N9O9, 679.776 / 679.36532; Thymogen and Thymagen, H-Glu-Trp-OH, C16H19N3O5, 333.344 / 333.13247; prothymosin alpha, the 109-residue precursor at roughly 12.5 kDa, which appears under shortened names and is an order of magnitude heavier. And Thymalin, an animal-tissue thymus extract with no sequence and no molecular weight at all: a "thymosin" certificate carrying no molecular weight is an extract, not this molecule.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definitionwith the N-terminal acetyl treated as an identity attribute rather than a related substance, and with aggregate content by SE-HPLC carried as a named release and stability attribute

3 Primary sources & evidence

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

Literature exists, is large, and is recorded here by study type and identifier only. In vitro, human primary cells: PMID 26096650, Expert Opin Biol Ther 2015, human monocyte-derived dendritic cells with TLR2, TLR3, TLR4 and TLR7/8 agonists. Reviews of largely in-vitro data: PMID 20699109, Peptides 2010, which also covers recombinant production; PMID 41373628, Int J Mol Sci 2025. Human randomized trials: ETASS, PMID 23327199, n=361, single-blind; tests, PMID 39814420, n=1,106, double-blind phase 3. Systematic review: PMID 33076834, 7 RCTs and 1,144 subjects, whose own stated limitations are that all trials were considered to have high risk of bias and all were from Chinese mainland. A cross-cutting finding for this category, and it applies here: marketing overwhelmingly cites the earlier, smaller trials and omits the later, larger ones, the ETASS-to-tests sequence being the example. No defined high-affinity receptor, no defined human dose-response relationship and no mechanistic account of the largest trial's result is established. NCT numbers appear only where a published paper reported them, so the absence of an NCT number here is not evidence that no registration exists.

4 Storage & specification

Storage

Lyophilized powder in foil-overwrapped or amber glass vials with a desiccant sachet in the shipper, stored at -20 degrees C plus or minus 5 degrees C, desiccated, protected from light. The cake is hygroscopic and the vial is brought to room temperature before the seal is broken so that moisture does not condense onto it. Shipped frozen on dry ice or a validated -20 degrees C phase-change pack with a temperature logger in the carton. Reference standards and retain samples at -80 degrees C plus or minus 10 degrees C.

Shelf life

The provisional retest interval is 24 months at -20 degrees C plus or minus 5 degrees C in the sealed original container, provisional pending the company's own stability data. The interval is dated on two attributes rather than on gross purity, because both are invisible in an area-percent figure: loss of the N-terminal acetyl at minus 42.037 Da, and Asn28 deamidation at plus 0.984 Da, the latter requiring not less than 30,000 resolving power to see at all. Aggregate content by SE-HPLC is a stability-indicating attribute here and is re-run at every retest.