ACE-031

1 Identity

Recombinant Fc-fusion glycoprotein — receptor ectodomain ligand trap. Not a chemically synthesized peptide. Related but chemically distinct agents traded near this name: bimagrumab (BYM338, a monoclonal antibody), and ActRIIA-Fc chimeras (the sotatercept architecture).

Sequence

No defined sequence — see the identity note, and the absence is the finding rather than a gap. The article is a disulfide-linked homodimer of a fusion polypeptide: the extracellular ligand-binding domain of human activin receptor type IIB joined to the hinge-CH2-CH3 region of human IgG1, expressed in mammalian cell culture and therefore N-glycosylated. Domain boundaries, hinge variant, Fc point mutations and the presence or absence of a purification tag differ between constructs that all trade under this one name, so no residue string is stated. The nearest fully disclosed construct located is a reagent catalog's own defined chimera — human Activin RIIB Ser19-Thr134 fused to human IgG1 Pro100-Lys330 with a 6-His tag, NS0-expressed — and it is disclosed precisely because it is a defined catalog reagent and not ACE-031.

Molecular formula

None stated, and none can be. A molecular formula implies a defined, unglycosylated chemical species; this article is glycosylated and its glycoform distribution is a property of the cell line and the culture process rather than of the sequence. Any formula printed for this article is therefore a category error, and the presence of one on a certificate is itself a defect.

Average mass

Not established — confirm against a reference standard before listing, and no such standard is in circulation. No exact mass exists for this article: the observed mass is a lot attribute, not a molecular constant. Size ranges only, and they are ranges and not masses: roughly 37-41 kDa predicted polypeptide monomer, roughly 75-80 kDa polypeptide dimer, roughly 110 kDa as the glycosylated dimer migrates. A reagent catalog prints 41 kDa predicted monomer against 60 kDa observed reduced on SDS-page for its own comparable chimera — a 19 kDa gap between calculation and observation that is glycan, and that gap is the reason no single number belongs on a certificate.

Monoisotopic mass

Not applicable and not computable. A monoisotopic mass requires a defined atom count; this article has none. No intact-mass acceptance criterion is to be written for it at any resolution.

Salt / variant note

Multiple architectures, one name — and none of them separable by mass. (1) The research-channel article: one seller states C3418H5188N928O1062S38, MW 77,489.82 for its 1 mg ACE-031. That formula is arithmetically self-consistent, but only under the older atomic-weight table: under IUPAC 2021 conventional weights it gives 77,490.82, and under the pre-2021 table it gives 77,489.81. The 1.00 Da spread is the atomic-weight convention for carbon at 3,418 carbons, not an arithmetic error — and that is itself the point, because an article whose average mass moves a whole dalton on the choice of reference table cannot carry a two-decimal specification. The deeper defect stands regardless: the formula describes an unglycosylated polypeptide dimer, a composition no mammalian-expressed Fc fusion can actually have, published with no construct map, no expression host and no glycan statement. (2) The defined reagent-catalog chimera: ActRIIB Ser19-Thr134 + IgG1 Pro100-Lys330 + 6-His, NS0-expressed, 41 kDa predicted monomer against 60 kDa observed reduced. (3) The same extracellular domain expressed in Sf 21 insect cells and carried in that same catalog: a different glycan class on an otherwise identical polypeptide, and therefore a different article. (4) The Activin RIIA-Fc chimeras the same catalog also lists: the sotatercept architecture, receptor A instead of B, and indistinguishable from ACE-031 by SDS-page, SE-HPLC or intact mass at any resolution a research-channel laboratory operates. (5) Plain human IgG1 Fc homodimer, roughly 50 kDa glycosylated and 25-27 kDa reduced: the cheapest substitution that still yields a protein band, and the only one in this list that a reduced CE-SDS gel catches on its own. (6) His-tagged against untagged versions of the same construct: roughly 1 kDa apart and an entire purification history apart.

2 Class & testing panel

Form

Single article

Testing panel

P4 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists and includes small early-phase human data, which is unusual for this catalog. Human, phase 1, randomized, placebo-controlled, single ascending dose, n=48 healthy postmenopausal women, sponsor-run: PMID 23169607. Human, randomized, placebo-controlled, pediatric, sponsor-run, terminated early on safety grounds after the second dosing regimen, with vascular findings named in the publication: PMID 27462804. Development was discontinued and the agent was never approved in any jurisdiction. Non-human primate (common marmoset), 2026: PMID 41686840, DOI 10.1371/journal.pone.0342666. Mouse pharmacology, reporting the functional and metabolic consequences of receptor blockade: PMID 24861054. Class reviews: PMID 41487000 (2026), PMID 42123420 (2026), PMID 27034275. Adjacent-agent literature belonging to bimagrumab and not to this article, which does not transfer to it: PMID 41772149 (human RCT, 2026), PMID 33439265, PMID 33597289, PMID 36098133, PMID 41873146, and meta-analyses PMID 39251484 and PMID 42530342. There is no completed pivotal trial, no marketing authorization anywhere, and very little independent non-sponsor literature.

4 Storage & specification

Storage

A formulated Fc-fusion glycoprotein of this class is stored at 2-8 degrees C as a liquid or at -80 degrees C plus or minus 10 degrees C as a frozen bulk, in single-use aliquots, protected from light, with no freeze-thaw cycles and never at -20 degrees C, which is the worst available temperature for a protein of this type. Lyophilized research preparations of comparable chimeras are commonly supplied with carrier protein to prevent adsorptive loss, itself a downstream-assay consideration that has to be declared. No vial is filled, no label is printed and no company storage condition is assigned.

Shelf life

No shelf life is assigned. No vial is filled against this record, so there is no retest date.