Follistatin 344

What Follistatin 344 is, and why it has no molecular formula

The first thing to settle is the name, because the number in it is not what most readers will assume.

Three figures circulate around this compound: 344, 315 and 288. They are not competing estimates of one quantity. FST344 is the name of a gene transcript, and the mature protein it yields is 315 residues, conventionally written FS-315; FS-288 is a shorter isoform. The 344 in the product name therefore identifies the transcript, while the residue count of the material itself is 315. Reading 344 as a chain length would propagate into any mass calculation built on it.

The stated weight supports 315 rather than 344: 34,800 daltons across 315 residues is about 110 per residue, the ordinary average for amino acids in a protein.

Three fields are marked not applicable above, for the same underlying reason: this is a protein, not a peptide. A formula could be written for a 315-residue chain, but it would run to several hundred carbon atoms and tell a reader nothing useful. Nothing about how this material behaves follows from counting its side-chain oxygens; size, folding and aggregation govern it instead.

There is likewise no CAS registry number. Registry numbers identify defined chemical substances, and a protein of this size sits outside what such a number usefully describes.

The quaternary structure is not recorded at source, so this page does not state whether the material is a single chain or an assembly. That gap matters for a protein, because it changes what a reduced-versus-non-reduced comparison should show.

Reconstitution and handling

Reconstitute gently. Add diluent slowly down the inside wall of the vial and let the solid dissolve without agitation, then swirl if needed.

Do not vortex. Proteins denature at air-liquid interfaces, and vortexing creates a very large one, so foaming here is not untidiness but the visible sign of a process that unfolds and aggregates protein.

Carrier protein is a genuine consideration. Adsorptive losses to plasticware and glass are severe for proteins at low concentration, and a carrier such as bovine or human serum albumin is conventionally included where the working concentration is dilute.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial reach room temperature before opening.

Aggregation is the dominant failure route, displacing the deamidation and oxidation chemistry that governs small peptides. It is irreversible, and concentration, agitation, temperature excursions and air-liquid interfaces all promote it.

Freeze-thaw is therefore damage, not untidiness. Each cycle concentrates solutes as ice forms and exposes protein to new interfaces. Aliquot on first reconstitution so no vial is thawed twice.

Reconstituted material should be held at 2 to 8 degrees C and used within a short working period, since a protein solution has a physical stability limit as well as a chemical one.

The ordinary chemical routes have not disappeared: a chain of 315 residues holds many asparagine, glutamine and aspartate positions capable of deamidation and isomerisation. They simply matter less, because one such event on a 34,800-dalton molecule is a far smaller proportional change than on a short peptide, and aggregation will generally cause a problem first.

These are storage conditions for the material, not dosing or administration guidance.

How Follistatin 344 is verified

Reversed-phase HPLC is the wrong method here, worth saying because it is the default for the rest of this catalogue. The acidic organic mobile phases that separate peptides denature proteins on the column, so an area-percent figure obtained that way does not describe the material as supplied.

SDS-PAGE is the appropriate identity check. A single band near 35 kilodaltons is expected, and its position confirms the chain length as no other routine method does. Running the gel both reduced and non-reduced is worth doing precisely because the quaternary structure is unstated: a shift between the two would indicate disulfide-linked assembly, its absence a single chain.

Size-exclusion chromatography reports what actually matters for a protein, the proportion of material present as aggregate rather than as the intended species. That figure, not a reversed-phase purity percentage, is the meaningful measure of quality.

Mass spectrometry at this size needs instrumentation suited to intact proteins, and returns a broader signal than a peptide's sharp molecular ion.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

Does the 344 in the name mean the protein is 344 residues long? No. FST344 designates the gene transcript. The mature protein it yields is 315 residues, and that is what the stated molecular weight of approximately 34,800 corresponds to, at roughly 110 daltons per residue.

Why is there no molecular formula or CAS number? Because this is a protein rather than a defined small molecule. A formula for a 315-residue chain would be accurate but useless, since nothing about the material's behaviour follows from its atom counts, and registry numbers do not usefully describe substances this size.

Full specifications for Follistatin 344.