SRP product and index pages do not print a sequence, CAS, UNII, molecular formula, or a public COA. Identity below is taken only from opened public registries and primary papers that name human follistatin, FST-344 / FS344 / preFS344, or the mature FS-315 chain produced from that precursor.

One-sentence identity: Follistatin-344 is the 344-amino-acid precursor isoform of human follistatin (UniProt P19883; NCBI NP_037541.1), a secreted glycoprotein / activin-binding protein that traps selected TGF-β-family ligands; after removal of a 29-residue signal peptide the circulating mature chain is the 315-residue FS-315 form. It is not a short research peptide like BPC-157, not the FST-317 / FS-288 splice product, not ACE-083, not stamulumab / MYO-029, and not an AAV or plasmid gene-therapy product.

What the molecule actually is. Shimasaki et al. 1988 (PMID 3380788; PMC 280398; full PDF opened) cloned human testicular cDNAs and the genomic locus. Three of eight sequenced cDNA clones predicted a 344-aa precursor (preFS344); the other five encoded a 317-aa precursor (preFS317) from alternative splicing. Mature follistatin was described as a single-chain gonadal protein that inhibits pituitary FSH release, with four contiguous domains encoded by separate exons, three of them similar to EGF and pancreatic secretory trypsin inhibitor. NCBI still labels the long RefSeq protein “follistatin isoform FST344 precursor” (NP_037541.1, 344 aa). UniProt displays that same 344-aa translation as isoform 1 and names it FS315, because the mature secreted chain after the 29-aa signal is 315 residues. NCATS UNII 506IY26H2I stores exactly that 315-aa mature sequence (starts GNCWLRQAKNGR…, ends …FPISSILEW).

Naming that must not be collapsed.

• FST-344 / FS344 / preFS344 = the 344-aa precursor (signal + mature FS-315). This is the cDNA used in the Nationwide / Mendell AAV construct rAAV1.CMV.huFollistatin344 / AAV1-FS344 (Haidet 2008; Kota 2009; Mendell 2015).
• FS-315 / FS315 / rhFS-315 = the mature circulating 315-aa chain after signal cleavage, with an acidic C-terminal tail. Inouye 1991 expressed this form in CHO cells. Schneyer 2004 showed FS315 is the major serum isoform and was undetectable in follicular fluid.
• FST-317 / preFS317 → mature FS-288 / rhFS-288. Shorter splice product. Higher heparin / cell-surface binding. Inouye 1991: rhFS-288 was 8–10× more potent than native porcine FS at suppressing FSH in rat pituitary cultures (ED50 9.6 ± 2.2 pM vs 86.7 ± 14.1 pM). Haidet 2008 explicitly avoided this form for gene transfer because of tissue binding and reproductive-axis concern.
• FS-303 / ~300-aa follicular-fluid form. Inouye 1991 and Schneyer 2004: most native porcine / human follicular-fluid FS is a proteolytically processed intermediate, neither FS-315 nor FS-288.
• UniProt’s displayed name “FS315” for a 344-aa sequence is not a third precursor. It is the same translation as NCBI FST344.

Registry chaos that must not be collapsed.

• PubChem has no compound CID for follistatin or FST-344. Marketplace pages that print CID 178101631 are pointing at a substance SID (IUPHAR), not a small-molecule CID. Looking up 178101631 as a CID returns an unrelated chloro-fluoro-indazole. CID 5281027 is an unrelated nucleotide-like structure. Neither is FST-344.
• CAS 80449-31-6, widely copied onto research-vial catalogs, resolved on PubChem xref/RN to ulinastatin (CID 105102). It is not used here.
• ChemIDplus CAS 117628-82-7 is a generic “Follistatin / Folstaxan / Gonadostatin” substance record. It is not a verified recombinant-FST-344 lot identifier and is not on the NCATS 506IY26H2I code list.
• NCATS 506IY26H2I is mature 315-aa follistatin, not a 344-aa precursor record and not an SRP-vial COA.
• DrugBank xref DB01666 on UniProt P19883 is D-myo-inositol hexasulphate, a ligand, not a follistatin drug.

Not printed on SRP pages and therefore not claimed as SRP-verified: amino-acid sequence, isoform (344 vs 315 vs 288 vs 303), signal-peptide status, CAS, UNII, glycosylation, disulfide pairing, endotoxin, folding, or a public COA file. The product page prints “COA: Certificate of Analysis available” and “Purity: ≥99%” as catalog bullets. Those bullets do not establish that the lyophilizate is folded, glycosylated FS-315.

This page is human FST-344 precursor / the FS-315 chain it can produce only. Catalog “myostatin inhibitor peptide” language is a nickname, not a chemical identity. FST-344 ≠ FS-288 ≠ ACE-083 ≠ stamulumab ≠ AAV product ≠ SRP vial.

Opened primary papers support a ligand-trap / extracellular neutralization model. It is not a treatment claim for an SRP vial. Observed means a measurement on the opened paper or registry. Proposed means a mechanistic inference the authors or this page mark as such. Class / adjacent means distinction biology (ACE-083, FS-288, antibody). Not shown means absent from the opened record.

Not shown on an opened page: a cloned “FST-344 receptor” (follistatin is the binder, not a GPCR agonist); human PK of an SRP vial; proof that research-market material is FS-315 rather than FS-288, FS-303, aggregated chain, or a peptide fragment; an FDA-approved FST-344 drug; equivalence of vial protein to rAAV1.CMV.huFollistatin344 or to ACE-083.

Label every row. FST-344 ≠ FS-288 ≠ ACE-083 ≠ stamulumab ≠ AAV product ≠ SRP vial. Human trial numbers are historical facts, not dosing instructions. Historical vg/kg and ACE-083 mg/muscle figures are study conditions for those products, not instructions for an SRP 1 mg vial, and they are not claims that research-grade material works in people.

Read the “what it did not show” column. Published study designs are historical facts from those papers. They are not a protocol. Historical AAV vg/kg and ACE-083 mg/muscle figures are study conditions for those products, not instructions for an SRP 1 mg vial. Label every human / ACE-083 / antibody row: NOT the SRP vial.

A. Protein / isoform / biochemistry

B. Animal / muscle / gene-therapy preclinical

These rows test transgenes, AAV vectors, or engineered Fc fusions, not an SRP 1 mg vial. Viral-genome and protein-dose figures are historical experimental exposures for those constructs.

C. Human / gene-therapy / ACE-083 trials (clearly labeled: NOT the SRP vial)

Opened human programs used AAV or plasmid DNA encoding FS344, or the ACE-083 fusion, or an anti-myostatin antibody. None of these records is a randomized evaluation of a 1 mg lyophilized FST-344 research vial. Doses below are trial-lot exposures for those products. No opened ClinicalTrials.gov record exists for a lyophilized FST-344 research-protein vial as the investigational product.

These are gaps in the opened record. Treating any of them as settled is incorrect.

• No FDA-approved therapeutic use of FST-344, FS-315, or recombinant follistatin. IUPHAR ligand 4933: approved false. NCATS 506IY26H2I: Approval Year Unknown. openFDA Drugs@FDA and labels: NOT_FOUND. ACE-083 Phase 2 programs were terminated. Stamulumab is a different molecule and did not become an approved dystrophy drug on the opened record.
• A research 1 mg vial is not rAAV1.CMV.huFollistatin344, not a Minicircle FST344 plasmid, and not ACE-083. Gene-therapy papers delivered DNA. ACE-083 is a modified FS–Fc fusion designed to stay in the injected muscle. Datta-Mannan 2013 found native FST315 poorly suited as a systemic parenteral biologic until it was Fc-fused and heparin-site–edited. (PMID 23249626.)
• Folding, disulfide pairing, glycosylation, heparin-binding competence, aggregation, and endotoxin of an SRP vial are not shown. Sidis 2001: N-terminal disulfide disruption dropped activin binding to <5%. UniProt/NCATS annotate 18 disulfides and N-glycans. Mass and a “≥99%” catalog bullet do not establish a functional glycoprotein. (PMID 11279126.)
• Isoform of the vial is not shown. SRP does not print sequence. FS-315, FS-288, FS-303, and truncated or misfolded chains are different biochemistry (Inouye 1991; Schneyer 2004; Lerch 2007).
• Human efficacy of vial protein is not established. Opened human work is gene transfer (n=6 BMD; n=6 sIBM with a published rebuttal; n=3 DMD registry; plasmid n=43 without an opened results paper) or ACE-083 (volume without consistent function). There is no opened RCT of lyophilized FST-344 protein.
• The Mendell sIBM functional claim is disputed. Greenberg 2017 titled those claims “unfounded.” This page reports both the 2017 abstract numbers and the existence of the letter. It does not adjudicate a winner. (PMID 28279643; PMID 28927986.)
• Muscle-volume increases are not automatically function. Glasser 2018: +8.9–14.5% volume, no significant strength change. Statland 2022 and Thomas 2022: significant TMV, no consistent functional / QoL benefit; both Phase 2 programs terminated. (PMID 29486514; PMID 35428982; PMID 35545446.)
• Lee 2001 short-form transgenic muscling is not FST-344 vial pharmacology. The spectacular +194–327% mouse line expressed the short human form from a muscle promoter for the life of the animal. (PMID 11459935.)
• Myostatin-pathway biology is not proof the vial “works.” Activin A, GDF11, and BMPs are also ligands (Sidis 2008; Lee 2010; UniProt). Broad ligand trapping is a risk context (pituitary FSH, reproduction, inflammation) as well as a muscle hypothesis. Haidet chose FS344 partly to reduce FS288-like FSH suppression — a concern, not a selling point.
• No opened chronic toxicology, carcinogenicity, or reproductive-tox package for a research-vial lot. Haidet’s normal mouse litter sizes apply to AAV1-FS344, not to a catalog protein.
• No opened human dose, bioavailability, or vial-to-serum exposure study that applies to an SRP 1 mg vial. Historical vg/kg and ACE-083 mg/muscle figures are not instructions.
• IUPHAR does not list an FST-344-specific ligand. Ligand 4933 is generic endogenous follistatin.

Each card is a single opened record. Historical AAV vg/kg and ACE-083 mg/muscle figures are study conditions for those products, not instructions for an SRP 1 mg vial. Human / ACE-083 / antibody cards are labeled NOT the SRP vial.

Follistatin-344 is an investigational laboratory research protein. It is not an FDA-approved drug for human use. This page is educational. It does not provide dosing, reconstitution, administration, or any human-use instructions.

Simple Research Peptides (SRP) materials are for laboratory research only and are not for human or veterinary use, consumption, administration, diagnosis, treatment, or therapeutic application.

Laboratory identity is the first practical issue. Opened papers and registries describe a 344-aa precursor (UniProt P19883; NCBI NP_037541.1) that matures to circulating FS-315 after signal 1–29, with 18 disulfides and N-glycans at Asn124 and Asn288. That is a folded glycoprotein, not a short linear peptide. SRP product pages do not print sequence, CAS, UNII, isoform, glycosylation, or a public COA. A method written for BPC-157, TB-500, ACE-083, stamulumab, FS-288, or an AAV construct is not automatically valid for this listing.

Confirm isoform, folding, glycosylation, disulfide pairing, and endotoxin before treating a vial as the literature article. Independently sourced research proteins are not established as equivalent to CHO-expressed rhFS-315, AAV-produced FS-315, rAAV1.CMV.huFollistatin344, or ACE-083. Gene-therapy papers used viral vectors, not a lyophilizate. Historical vg/kg and ACE-083 mg/muscle figures are study conditions for those products. They are not a reconstitution scheme and they are not a use guide for an SRP 1 mg vial.

Biological inference has the same problem. The opened record is strong on isoform biochemistry and ligand-trap structure, strong on mouse/primate AAV-FS344 and transgenic short-form muscling, thin and contested on human gene transfer, negative-to-terminated on ACE-083 function, and empty on research-vial lots. That is not a completed muscle-drug program for a 1 mg lyophilizate and is not evidence for research-market vials.

Sources actually opened for this draft. Do not add PMIDs or NCTs that are not on the allowed list. Every NCT is gene therapy, ACE-083, or stamulumab — NOT the SRP vial.

Allowed PMID list used on this page (biochemistry): 3380788, 1906804, 11279126, 15472207, 16198295, 16482217, 17409095, 18535106, 19644449, 23249626. Animal/GT: 11459935, 20810712, 18334646, 20368179, 22711699 (FS-288 AAV — label NOT FS344), 24627466, 19208403. Human/adjacent NOT the SRP vial: 25322757, 27858738, 28279643, 28927986, 29486514, 35428982, 35545446, 18335515. Unused (opened as UniProt/CT.gov xref only, not separately opened as papers): PMID 15340161, PMID 19054851, PMID 15489334, PMID 20843798, PMID 31215115, PMID 28257634, PMID 40152935, PMID 17164329, PMID 39086961, PMID 32426485, PMID 31327755. No other PMIDs were added. No NCT was invented. No FST-344-specific CAS was claimed. Marketplace CAS 80449-31-6 (ulinastatin) was rejected.

Product links are research materials, not treatment recommendations. Opened SRP page: Follistatin-344 (1 mg Vial); category Muscle Growth Research (store taxonomy, not a clinical indication). Footer: for laboratory research only; not for human or animal use, consumption, administration, diagnosis, treatment, or therapeutic application. Sequence, CAS, UNII, molecular formula, isoform, glycosylation, and a public COA were not printed on the fetched page. Do not confuse with FS-288, ACE-083, stamulumab / MYO-029, FSTL3, rAAV1.CMV.huFollistatin344, or short peptides such as BPC-157 / TB-500.