Thymosin Alpha-1: structure and analysis

What is Thymosin Alpha-1?

Thymosin alpha-1 is a 28-amino-acid peptide with an N-terminally acetylated terminus, originally isolated from thymic tissue and produced synthetically here.

The acetylation is a defining structural feature rather than a detail: the non-acetylated 28-residue sequence is a different compound.

Despite the shared name, this peptide is unrelated in structure to thymosin beta-4, the sequence supplied as TB-500. The alpha and beta thymosins are separate families that happen to have been isolated from the same tissue.

How is Thymosin Alpha-1 produced?

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

What are the molecular figures for Thymosin Alpha-1?

Calculated from the formula C129H215N33O55, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

Two masses describe this molecule and they are not the same number. The monoisotopic mass assumes every carbon is carbon-12; the tallest peak in the isotope envelope sits 1 carbon-13 substitution above it, because for a molecule with 129 carbons that is the most probable composition. A specification or a database quoting the higher figure is not necessarily wrong — it is quoting the other peak, and both are given here.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of Thymosin Alpha-1?

Thymosin Alpha-1 is 28 residues long. Written in the one-letter amino-acid code, as the cited record states it:

The sequence is what an identity test resolves. The mass a spectrometer is compared against is the mass this chain implies, which is why a single missing or substituted residue changes the result by an amount that cannot be mistaken for instrument variation — the deletion is detectable rather than invisible.

Sequence information describes the molecule, not the material in a vial. What establishes a specific batch is the identity method and result on its certificate.

How does Thymosin Alpha-1 compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of Thymosin Alpha-1 confirmed?

Mass spectrometry confirms the 28-residue chain and the N-terminal acetyl group. Acetylation adds forty-two mass units, a large enough increment that acetylated and non-acetylated species are unambiguously distinguishable.

Confirming acetylation is the identity question specific to this compound, and it is a straightforward one to answer given the size of the mass shift.

Which impurities can appear in Thymosin Alpha-1?

At 28 residues, deletion and truncation products are the expected impurity class and are closely spaced chromatographically — the same consideration that applies to sermorelin at 29 residues.

Incomplete acetylation is the modification-specific impurity, and it is comparatively easy to resolve: capping the N-terminal amine removes a positive charge and increases hydrophobicity, so the two species separate on reversed phase as well as differing in mass.

What does a certificate of analysis for Thymosin Alpha-1 report?

A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is Thymosin Alpha-1 for human use?

No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.

References

• Thymalfasin (thymosin alpha-1) — PubChem, National Library of Medicine
• Prothymosin alpha — human — UniProt Knowledgebase
• Thymalfasin — ChEMBL, European Bioinformatics Institute
• Characterization of the immunoregulatory properties of thymosin alpha 1 on interleukin-2 production and interleukin-2 receptor expression in normal human lymphocytes — Int J Immunopharmacol, 1989