Research library / Compounds

What is ?

A 28-residue peptide first sequenced from calf thymus in 1977.

is a peptide of 28 amino acids, first isolated from calf thymus and sequenced in 1977. It is one of several peptides found in a thymus extract called thymosin fraction 5, and it has been studied for its role in the development and function of T cells. Prism Labs supplies it as a 5 mg lyophilized vial.

Prism Labs editorial · Updated September 10, 2026 · 3 min read

Lyophilized vial5mg · 99.60% purity$49.99View product

What it is

The synthetic version has the sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN: 28 residues with an acetyl group on the N-terminus. The reference record lists the formula C129H215N33O55 and a molecular weight of 3108.3 g/mol (PubChem CID 16130571).

The 1977 paper described it as heat-stable and highly acidic. Nearly a third of its residues are aspartic or glutamic acid.

In clinical literature the synthetic peptide is called thymalfasin.

Sources: [3] PubChem · reference structure · [1] PNAS · 1977

Where it came from

In the 1970s, Allan Goldstein’s group purified peptides from thymosin fraction 5. The 28-residue alpha-1 peptide was isolated and sequenced in 1977, in a paper that also proposed a naming system for the whole family.

In 1984, researchers found that in rat thymus it exists mostly as part of a larger protein, prothymosin alpha, which carries the same sequence at its N-terminus.

Sources: [1] PNAS · 1977 · [2] PNAS · 1984

Lyophilized vial from Prism Labs — Every lot ships with its own certificate of analysis.

Not the same as

Both names start with “thymosin” because both proteins were first isolated from thymus extracts, but they are unrelated. Thymosin beta-4 is a 43-residue actin-binding protein found in most cells; the alpha-1 peptide has 28 residues, a different sequence and a different research literature. is based on thymosin beta-4, not on this peptide: What is ?

Sources: [7] Journal of Biological Chemistry · 1991 · [1] PNAS · 1977

What researchers have studied

Research spans laboratory and clinical work:

T-cell development and function, the original reason for studying thymus peptides.
Immune signaling in cell and animal models.
Blood levels in health and disease, reviewed in 2018.
Clinical studies under the name thymalfasin, summarized in reviews from 2001 and 2020.

These are observations in laboratory models. They are not evidence about any use in people.

Sources: [1] PNAS · 1977 · [6] Expert Opinion on Biological Therapy · 2018 · [4] American Journal of Health-System Pharmacy · 2001 · [5] World Journal of Virology · 2020

How it is supplied and stored

ships as a lyophilized (freeze-dried) powder in 5 mg vials. The powder is stable at room temperature in transit. For lab use it is reconstituted with bacteriostatic water such as .

Concentration is content divided by volume: 5 mg in 2 mL gives 2.5 mg per mL. The reconstitution calculator handles other combinations.

For storage before and after reconstitution, see how to store lyophilized peptides.

How to verify a batch

Every lot has its own certificate of analysis from an independent lab. Read three results separately:

Identity: confirms the expected compound was detected.
Purity: the share of the measured material that is the intended compound.
Content: the amount measured, compared with the label.

Then match the lot number on your vial or bottle to the report, and use the report’s verification link to confirm it with the testing lab. Step by step: how to read a peptide COA.