FGL

1 Identity

Neuroactive regulatory peptide — synthetic sequence from the FG loop of the second fibronectin type III module of NCAM; traded as both a linear monomer and a four-arm dendrimer. and [Glp1]-FGL peptide. CAS 499993-62-3 is printed for the linear monomer.

Sequence

Two sequences trade under this name and the certificate must state which it covers. Monomer: H-Glu-Val-Tyr-Val-Val-Ala-Glu-Asn-Gln-Gln-Gly-Lys-Ser-Lys-Ala-OH (EVYVVAENQQGKSKA), 15-residue all-L linear peptide, free N-terminus, free C-terminal carboxylic acid, no cysteine, no disulfide, no acylation, no non-proteinogenic residue. Pyroglutamate form: pGlu-Val-Tyr-Val-Val-Ala-Glu-Asn-Gln-Gln-Gly-Lys-Ser-Lys-Ala, in which Glu1 has cyclized to pyroglutamate with loss of water. Four-arm dendrimer: four copies of the monomer assembled through their C-termini onto a branched lysine core; branch architecture, core composition and any spacer must be declared in writing and drawn before any figure is stated. The counterion is trifluoroacetate or acetate and must be quantified: the monomer carries two lysine side chains and the dendrimer adds the lysine core on top of them, so basic-residue count, and therefore salt burden, differ substantially between the two forms.

Molecular formula

C71H116N20O25 (linear monomer, free acid). C71H114N20O24 (pGlu1 form, free acid). The dendrimer has NO fixed formula until the supplier draws the core, and none is stated here.

Average mass

Linear monomer 1649.824 Da (C71H116N20O25). PGlu1 form 1631.809 Da (C71H114N20O24), the monomer minus one water. Two conventions are in circulation, and both figures should be read with that in mind: tabulations built on pre-2021 atomic weights give 1649.800 and 1631.784, while IUPAC 2021 conventional atomic weights give 1649.824 and 1631.809. The 0.024 Da spread is convention rather than error, and neither set is a correction of the other. One institutional supplier prints 1631.81, which agrees with the modern value; a research-chemical seller prints 1649.8, which rounds both. Four-arm dendrimer: not established and deliberately not stated. Four monomer equivalents sum to 6599.30 Da before the water lost at each branch amide and before the mass of the lysine core and any spacer are added, so that sum is a floor and not a mass; it places the construct in the 6.7 to 7.0 kDa region, and no single figure can be fixed until the supplier draws the branch architecture.

Monoisotopic mass

Linear monomer 1648.84205 Da neutral. Working ions: [M+2H]2+ m/z 825.42830, [M+3H]3+ m/z 550.62129, [M+H]+ m/z 1649.84933. The 2+ and 3+ species dominate on a peptide with two Lys plus the N-terminus. PGlu1 form 1630.83148 Da neutral — cyclization removes the free N-terminal amine, so the pGlu form ionizes less readily and its charge envelope shifts, which is a second, orthogonal signal that the wrong form has been shipped, on top of the 18.02 Da difference. A plus or minus 5 ppm window on the monomer neutral is plus or minus 0.0082 Da. NO monoisotopic figure is stated for the dendrimer, which is characterized by MALDI average mass rather than by an isotopically resolved envelope.

Salt / variant note

Multi-molecule name, and the split runs along the institutional against research-chemical boundary rather than between good and bad suppliers. (1) linear monomer, free GLU1: C71H116N20O25, 1649.824 average / 1648.84205 monoisotopic. This is what the research-chemical sellers ship; two of them print exactly this formula and this mass. (2) pyroglutamate form: C71H114N20O24, 1631.809 / 1630.83148, the monomer minus one water, 18.02 Da light. One institutional supplier sells this under the bare name "FGL Peptide", and a reagent catalog sells it as "[Glp1]-FGL peptide (acetate)". Two suppliers, one product name, AN 18 Da difference — the same pattern that appears elsewhere in the catalog in a different class, and detectable by arithmetic on the certificate alone. (3) four-arm dendrimer on a branched lysine core, roughly 6.7 to 7.0 kDa, used in a substantial part of the published work; the characteristic manufacturing defect is the des-arm species, each missing arm removing about 1631.8 Da average, so a three-arm construct runs near 5.3 kDa and a two-arm near 3.65 kDa — both co-migrating with the full construct on reversed phase and separating cleanly by size exclusion. (4) FLUORESCEIN-labeled monomer, listed by one supplier and sold by the nanomole rather than by mass, which is a different unit basis and is not comparable on a per-milligram basis.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definitionfor the linear monomer. The four-arm dendrimer is not a P1 article: it is a branched multimeric construct whose release requires size-exclusion chromatography and MALDI average-mass characterization rather than isotopically resolved accurate mass, and the panel cannot be finalized until the supplier draws the core

3 Primary sources & evidence

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

Study types only, with the form caveat attached to every line. The published work on NCAM FG-loop-derived peptides is in vitro and rodent, and A substantial part of it used the four-arm dendrimer rather than the linear monomer — which means the literature and the traded article are frequently not the same substance. No citation is carried on a product page without stating which construct that paper used, and the construct is printed per paper in the same type size as the citation. No registered human trial under this name was identified. No marketing authorization in any jurisdiction.

4 Storage & specification

Storage

Lyophilized powder. Store at -20 degrees C or below, desiccated, protected from light; the single tyrosine is the oxidation-sensitive residue. If the dendrimeric form is confirmed, the storage condition is unchanged but the retest interval shortens until in-house solid-state data on the branched construct exist, because the branched construct behaves differently on reconstitution from the way the monomer does. Acetate is preferred over trifluoroacetate and is specified on the purchase order.

Shelf life

Provisional 24-month retest interval at -20 degrees C, desiccated, for the linear monomer; provisional 12 months for the DENDRIMER, the shorter interval reflecting an absence of data rather than a known instability, and labeled in those words. Both figures are provisional, and both are replaced by the first in-house stability pull under the company's ICH-format program. Tracked attributes for the monomer: tyrosine oxidation, water, counterion, and Asn8 deamidation (+0.984 Da), which is a real pathway on an Asn-Gln sequence and is close enough to the pGlu mass shift in direction that the method must distinguish the two. Tracked attribute for the dendrimer: des-arm content by size exclusion.