GDF-8 (Myostatin)

What GDF-8 is, and why it has no molecular formula

GDF-8 is supplied as a homodimer: two identical chains of 109 residues each, assembled as a pair. The product page is explicit that the pair, rather than one chain, is the material.

That distinction carries through everything below. The two stated weights describe different things: about 12,400 daltons is one chain, about 25,000 the assembled protein. They agree, since twice 12,400 is 24,800, and the monomer figure divided by 109 residues gives roughly 114 daltons each, an ordinary average. A reader who takes 12,400 as the product's weight has the monomer, not what the vial contains.

Three fields are marked not applicable above, for the reason that applies to any protein rather than through omission. A molecular formula could be written for a 109-residue chain, but it would tell a reader nothing they could use: none of this material's behaviour follows from counting its atoms. Size, folding and the integrity of the dimer govern it instead.

There is likewise no CAS registry number, which is expected. Registry numbers identify defined chemical substances, and a recombinant protein assembly is not what such a number usefully describes.

The dimeric architecture gives a direct handle on verification: an assembly of two chains and a single free chain behave differently under analysis, which the testing section turns into a concrete check.

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 the visible sign of a process that unfolds and aggregates protein rather than mere untidiness.

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.

Reducing agents warrant care. Where a dimer is held together covalently, a reducing agent separates it into single chains, and separated chains are not the material described by the specification above.

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.

Dissociation is the failure mode specific to this material. A protein whose defining feature is an assembly of two chains can lose that assembly, and separated chains are neither the specified substance nor reliably recoverable as it. Conditions that unfold protein generally promote dissociation as well.

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.

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

How GDF-8 is verified

Reversed-phase HPLC is the wrong method here, worth stating because it is the default across 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 run both reduced and non-reduced is the informative check, and on this material it is unusually direct. Non-reduced, correctly assembled protein runs near 25 kilodaltons. Reduced, it should resolve to single chains at roughly half that, near 12,400. Seeing the pair of results together confirms both the chain length and the assembly, which neither condition establishes alone. A non-reduced sample already running at monomer size indicates dissociated material.

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

Mass spectrometry at this size requires 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

Is the molecular weight 25,000 or 12,400? Both figures are correct but describe different things. About 12,400 is a single 109-residue chain; about 25,000 is the assembled homodimer, which is what the vial contains. Twice the monomer figure is 24,800, so the two are consistent.

Why is there no molecular formula or CAS number? Because this is a recombinant protein rather than a defined small molecule. A formula for a 109-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 assemblies of this kind.

Full specifications for GDF-8 (Myostatin).