Why Does Full-Length Thymosin Beta-4 Cost More Than TB-500?

Two materials trade under the name TB-500: the 43-residue protein Thymosin β4 and the seven-residue fragment Ac-LKKTETQ. Their prices differ by a wide margin, and the difference is not arbitrary. It follows from how peptides are synthesized, and it is one of the few signals available before any analysis is done.

Yield compounds with length

Solid-phase synthesis adds one residue per cycle, and no cycle is perfectly complete. At 99 percent efficiency per coupling, a seven-residue chain requires six couplings and about 94 percent of chains come out full-length. A 43-residue chain requires 42, and the figure is about 66 percent. At 98 percent per coupling the same comparison is 89 percent against 43 percent. The longer chain starts purification with far more by-product to remove.

Purification gets harder, not just longer

The by-products of a long synthesis are mostly chains missing a single residue. A chain of 42 residues differs from the 43-residue target by about two percent of its mass and behaves almost identically on a column. Separating them requires shallower gradients, narrower fraction cuts and often more than one pass, and each step discards material. For a seven-residue peptide, a chain missing one residue differs by roughly a seventh of the molecule and separates readily.

Reagents and time

Each cycle consumes protected amino acid, coupling reagent and solvent, in excess. Forty-two cycles consume about seven times what six cycles do, before any repeat couplings at difficult positions. Instrument time scales the same way.

Analysis is more demanding

Confirming a 4963 Da molecule takes more than confirming an 889 Da one. The isotope pattern is broader, several charge states have to be reconciled, and distinguishing the target from a near-identical deletion sequence by mass requires better resolution.

Reading a price

None of this fixes what either material should cost. It does establish a direction: material offered as full-length Thymosin β4 at a price typical of the fragment raises the identity question before any other. The specification resolves it. A stated molecular weight near 889 Da, or the sequence Ac-LKKTETQ, identifies the fragment regardless of the name on the listing.

What FLASK lists

Materials listed as TB-500 on this site are the heptapeptide fragment: sequence Ac-LKKTETQ, molecular weight 889.02 Da, CAS 885340-08-9. FLASK does not currently list full-length Thymosin β4.

Frequently asked questions

Why is the 43-residue peptide harder to purify?

A chain missing one residue differs from the target by about two percent of its mass and behaves almost identically on a column, so separation needs shallower gradients and more passes.

Does price alone identify which molecule is in a listing?

No. It establishes a direction only. A stated molecular weight near 889 Da or the sequence Ac-LKKTETQ identifies the fragment regardless of the name.

Which material does FLASK list as TB-500?

The heptapeptide fragment. FLASK does not currently list full-length thymosin beta-4.