BPC-157 vs. TB-500: A Structural Comparison

Last reviewed: August 2, 2026

These two sequences are routinely discussed together and are chemically quite unlike one another — different lengths, different charge states, different terminal chemistry, and different handling consequences that follow from all three. This comparison is restricted to chemistry and laboratory handling: composition, structure, stability and supply form. It does not describe what either compound does in any organism, and nothing here is guidance on use.

Composition at a Glance

BPC-157

Class: linear pentadecapeptide — 15 residues
Sequence: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val (GEPPPGKPADDAGLV)
Molecular formula: C₆₂H₉₈N₁₆O₂₂
Average molecular weight: 1,419.5 g/mol
CAS: 137525-51-0 · PubChem CID: 9941957
Termini: free N-terminal amine, free C-terminal acid — unmodified at both ends

TB-500

Class: linear, N-acetylated heptapeptide — 7 residues
Sequence: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ)
Molecular formula: C₃₈H₆₈N₁₀O₁₄
Average molecular weight: 889.0 g/mol
CAS: 885340-08-9 · PubChem CID: 62707662
Termini: acetylated N-terminus, free C-terminal acid

BPC-157 is a 15-residue sequence corresponding to a fragment of a larger naturally occurring human protein, first described in the 1990s. TB-500 corresponds to a short region of thymosin β4.

TB-500 Is Not Thymosin β4

This is the most consequential point of confusion in the category, and it is a straightforward matter of molecular weight.

Thymosin β4 is a 43-residue protein of roughly 4,960 g/mol. TB-500 as supplied in the research market is the acetylated seven-residue sequence above, at 889.0 g/mol — about one fifth the mass and one sixth the chain length. The two are frequently listed as synonyms and they are not the same molecule.

The check takes seconds. A certificate reporting an observed mass near 889 describes the heptapeptide; one reporting a mass near 4,960 describes the full-length protein. If a listing offers "TB-500 (Thymosin β4)" without specifying which, the sequence and molecular weight on the paperwork settle it — and if the paperwork does not state them, that is the more informative finding. See how to read a peptide COA for the rest of the identity block.

Charge and Isoelectric Behaviour

Counting ionisable groups at around pH 7 gives two quite different pictures.

BPC-157 carries one glutamate, two aspartates and a free C-terminal acid on the negative side, against one lysine and a free N-terminal amine on the positive side — a net charge of approximately −2. It is an acidic peptide with an isoelectric point in the region of pH 4.

TB-500 carries two lysines on the positive side against one glutamate and a free C-terminal acid on the negative side. Because the N-terminus is acetylated it contributes no positive charge, leaving a net charge close to zero through the near-neutral range and placing its isoelectric point in that region.

A peptide is least soluble near its pI, so on charge alone TB-500 would look like the more awkward of the two to dissolve at neutral pH. In practice it is not, because charge is only one of the two axes that govern solubility: five of its seven residues are polar or charged, and that composition keeps it readily water-soluble despite the near-zero net charge. It is a clean illustration of why the solubility calculation uses hydrophobicity alongside charge rather than charge alone.

Backbone Character: Proline vs. Polar

Four of BPC-157's fifteen residues are proline, including a Pro-Pro-Pro run at positions 3 to 5. Proline is the one cyclic amino acid: its side chain loops back onto the backbone nitrogen, which fixes the backbone dihedral angle within a narrow range and removes the amide N–H that other residues use for hydrogen bonding. Proline-rich stretches are therefore conformationally restricted rather than freely flexible, and they are poor substrates for many endoproteases, which require a more extended backbone geometry in the binding cleft. A 27% proline content is a defining structural feature of this sequence.

TB-500 has no proline. It is a short, flexible, polar chain — two lysines, two threonines, a glutamate and a C-terminal glutamine — whose N-terminal acetyl group caps the chain against aminopeptidases that act on a free N-terminal amine. Its stability characteristics come from that cap and from its brevity, not from backbone rigidity.

Degradation-Relevant Motifs

Reading each sequence for the residues that cause trouble in storage:

BPC-157 contains adjacent aspartates at positions 10 and 11. Aspartate is the residue most prone to aspartimide formation — cyclisation to a succinimide that reopens to a mixture of aspartate and iso-aspartate. The rearrangement leaves molecular mass unchanged, so it is invisible to a mass measurement and appears only as an additional chromatographic peak.
TB-500 ends in glutamine, which can deamidate to glutamate with a +0.98 Da mass shift. Glutamine deamidates considerably more slowly than asparagine, and both processes accelerate at alkaline pH.
Neither contains cysteine, methionine or tryptophan. Neither is therefore notably oxidation-sensitive or photolabile, and neither can form a disulfide. This also means that where a strongly dissolving solvent is genuinely required, the usual prohibition on DMSO for thiol- and thioether-containing sequences does not apply to either.

Standard storage and handling practice covers both: dry, cold, dark, and aliquoted once reconstituted.

Supply Form and Counter-Ion Mass

Both are supplied as lyophilised solids in sealed vials at milligram scale, and both are normally isolated as the trifluoroacetate or acetate salt following reversed-phase purification.

The counter-ion load is set by the peptide's charge state under purification conditions, not at neutral pH — which is a distinction worth holding onto. In 0.1% trifluoroacetic acid at around pH 2 the carboxylates of both peptides are protonated and neutral, leaving BPC-157 at approximately +2 (lysine plus N-terminal amine) and TB-500 also at approximately +2 (two lysines). Both therefore tend to carry a comparable absolute counter-ion load of roughly two trifluoroacetates, at 113.02 g/mol each.

The same absolute load is a very different mass fraction on the two molecules:

BPC-157: 226.04 / (1,419.5 + 226.04) = 13.7% of the solid
TB-500: 226.04 / (889.0 + 226.04) = 20.3% of the solid

Smaller peptides pay proportionally more mass for the same charge, which is why net peptide content tends to run lower on short sequences and why a nominal concentration calculated straight from the labelled quantity is further off for TB-500 than for BPC-157. The purity vs. content guide works the correction through.

Analytical Signature

Both are straightforward on standard reversed-phase C18 with a water/acetonitrile gradient and UV detection at 214 nm. BPC-157, with its proline-rich and comparatively hydrophilic composition, elutes early; TB-500, short and polar, also elutes early, and a shallow gradient is worth using on both to resolve close-running impurities.

By electrospray mass spectrometry, BPC-157 at 1,419.5 g/mol presents principally as [M+H]⁺ near m/z 1,420.5 and [M+2H]²⁺ near m/z 710.8. TB-500 at 889.0 g/mol presents as [M+H]⁺ near m/z 890.0, with the doubly charged ion near m/z 445.5. Both are small enough that the singly charged ion dominates, which makes the spectra easy to read against the theoretical mass.

Current listings, strengths and composition data are on the BPC-157 and TB-500 product pages.