Recombinant Human Activin A Protein

What it means: This Activin A is produced in HEK293 human cells, a human embryonic kidney cell line widely used to make secreted human proteins, rather than in bacteria or insect cells.

Why it matters:

• Activin A is a disulfide-linked homodimer; expression in HEK293 supports mammalian protein folding and post-translational processing of the dimer.
• Production in a human host avoids bacterial host-cell contaminants that can affect sensitive stem-cell cultures.
• The manufacturer makes the protein in an animal-free, xeno-free format, which suits fully human culture systems.

How to interpret here: An expression system of HEK293 means the ligand was made and secreted by human cells. This is consistent with its main use in human iPSC and ESC differentiation, definitive endoderm induction and organoid protocols.

Tip: When switching from an Activin A made in another host, re-titrate the working dose rather than assuming the same activity per microgram.

What it means: The protein is Tag-free: no His, Fc, GST or other affinity tag is fused to the Activin A sequence, and no tag needs to be removed before use.

Why it matters:

• A tag adds extra amino acids that can change folding, receptor binding, stability or the apparent molecular weight of a small signaling protein.
• In defined stem-cell and organoid media, every added component is a variable; a tag-free protein keeps the ligand as close as possible to the native sequence.
• Tag-free proteins are also preferred when results will be compared with published protocols that used untagged growth factors.

How to interpret here: Tag-free here means the vial contains only the Activin A protein. It cannot be captured or detected with anti-His, anti-GST or Protein A reagents, so detection needs an antibody against Activin A itself.

What it means: Purity of >95% by SDS-PAGE means that when the protein is run on a denaturing gel and stained, at least 95% of the stained protein is the Activin A band. It is the release specification the manufacturer applies to every lot.

Why it matters:

• High purity limits other proteins in the vial that could act on cells or interfere with downstream readouts.
• Dosing is done by protein mass, so a pure preparation makes the amount of active ligand added more accurate and comparable between experiments.
• Purity is measured together with endotoxin (<0.5 EU/µg) and biological activity before each lot is released.

How to interpret here: A specification of >95% by SDS-PAGE is a minimum value. The exact result for each lot is on the Certificate of Analysis (CoA), available from BioHippo on request.

Tip: SDS-PAGE purity shows how clean the preparation is, not how active it is; check the activity data separately.

What it means: The species is Human: the amino-acid sequence is that of human Activin A (inhibin beta A subunit, gene INHBA, UniProt P08476). The protein is also produced in human cells, so both the sequence and the expression host are human.

Why it matters:

• Matching the species of the growth factor to the species of the cells avoids differences in receptor affinity between species.
• Human sequence is the usual choice for human iPSC, ESC, organoid and primary human-cell work.
• Recording the species in protocols matters because the same protein is sold from several species by many suppliers.

How to interpret here: Human here refers to the protein sequence. When reproducing a published protocol, check that the protocol also used Human Activin A; if it used a protein from another species, the working concentration may need adjusting.

What it means: The protein is supplied Lyophilized, that is freeze-dried to a powder, from a carrier-protein-free preparation and without carrier protein.

Why it matters:

• Lyophilized protein is more stable during storage than a solution, which gives a long shelf life when stored correctly.
• The stock concentration is set at reconstitution, so it can be matched to the volumes used in the protocol.
• As supplied, store at −20°C to −80°C for up to 12 months from receipt; after reconstitution keep it at 2°C to 8°C for up to 1 month or at −20°C to −80°C for up to 3 months.

How to interpret here: Lyophilized means the vial must be reconstituted before use: briefly centrifuge the vial before opening, then reconstitute in sterile PBS containing 0.1% endotoxin-free recombinant human serum albumin, mix gently without aggressive vortexing and prepare single-use aliquots under sterile conditions.

Tip: Avoid repeated freeze–thaw cycles of the reconstituted protein; a manual-defrost freezer is recommended.

What it means: The molecular weight is Approximately 25 kDa. The manufacturer describes the protein as a disulfide-linked homodimer of two inhibin beta A chains.

Why it matters:

• Molecular weight is the first check of identity when the protein is run on a gel or analysed by other methods.
• For a dimeric protein, the band observed depends on whether the sample is reduced or non-reduced, so note the gel conditions when comparing results.
• The manufacturer gives a nominal value and refers to lot-level data for the exact profile.

How to interpret here: Approximately 25 kDa is a nominal value. Refer to the lot-specific Certificate of Analysis (CoA) and SDS-PAGE profile, available from BioHippo on request, for the data that apply to each lot.

What it means: Biological activity is tested by the ability of Activin A to inhibit proliferation of murine MPC-11 plasmacytoma cells. The typical result is EC50 6.68–10.02 ng/mL, the concentration that gives half of the maximal effect.

Why it matters:

• A cell-based activity test confirms that the protein is functionally active, which purity alone cannot show.
• The EC50 gives a reference point for comparing lots and for comparing this product with other Activin A preparations tested in the same assay.
• Activity is checked on each lot together with purity and endotoxin before release.

How to interpret here: EC50 6.68–10.02 ng/mL describes potency in the MPC-11 assay. It is not a recommended working dose: concentrations used for stem-cell differentiation depend on cell line, medium, stage and exposure time and should be optimized for each protocol.