PE-22-28

1 Identity

Base synthetic linear heptapeptide. All seven residues L and proteinogenic; free N-terminal alpha-amino group and free C-terminal carboxylic acid; no acylation, no amidation, no cyclization, no disulfide, no metal, no non-proteinogenic residue. One tryptophan, which is the only strong chromophore and the only oxidation-labile center; one arginine, which is the only basic side chain; one serine. Small, soluble, and unremarkable as chemistry — the difficulty on this article is commercial and evidentiary, not structural. and CAS 1801959-12-5. Sold under names that are not its own: "spadin" and "spadin analog" are used for it in the research-chemical channel and both are inaccurate — spadin is the 17-residue parent, PE 12-28, and this article is a 7-residue peptide corresponding to residues 22-28 of the sortilin/NTSR3 propeptide. The numbering is positional, not a lot code and not a series number.

Sequence

H-Gly-Val-Ser-Trp-Gly-Leu-Arg-OH (GVSWGLR), seven residues, all L and proteinogenic. Free N-terminal alpha-amino group, free C-terminal carboxylic acid; no acetylation, no amidation, no cyclization, no disulfide. The sequence, the formula, the average mass and the CAS rest on three independent documents that agree, one of them an institutional supplier publishing a purity method. The chemistry and the sequence-to-CAS link are established; no authenticated reference standard is held, so no lot has been confirmed against one. Residue order remains an MS/MS release test on the first lot from every supplier: seven residues is short enough that permutation and epimerization are cheap and invisible to mass. A chiral method sits on the release panel even though the specification contains no D-residue, and the reason is stated rather than assumed: at the sub-nanomolar working concentrations at which this article is used, an epimeric impurity is detectable neither by activity nor by mass.

Molecular formula

C35H55N11O9 as the free peptide. Supplied as the acetate salt, which is not a fixed stoichiometry and is specified as a percentage range rather than folded into a formula; the shipped mass is peptide plus counterion plus water, and no single formula describes the vial.

Average mass

773.893 Da (C35H55N11O9), on IUPAC 2021 abridged conventional atomic weights (C 12.011, H 1.008, N 14.007, O 15.999) from the formula and independently reconstructed residue-by-residue from GVSWGLR; the two routes agree to the digit. One institutional supplier publishes 773.89 for the same formula and two research-channel sellers publish 773.89 and 773.8947; all agree within rounding. As the 1:1 acetate salt the formula unit is C37H59N11O11 at 833.945 — a 7.2 percent difference from the free-peptide figure, which is why the counterion percentage is a certificate line and not a footnote.

Monoisotopic mass

773.41842 Da neutral (C35H55N11O9); [M+H]+ 774.42570; [M+2H]2+ m/z 387.71649; [M-H]- 773.41114. Identity window on [M+H]+ at plus or minus 5 ppm is plus or minus 0.0039 Da. The C-terminal amide is 772.43441 neutral, [M+H]+ 773.44169 — 0.984 Da below parent and unresolved below about 30,000 resolving power. Single tryptophan oxidation gives 789.41334 neutral, plus 15.995 Da.

Salt / variant note

(1) epimers and permutations, invisible to mass at any resolution: any D-residue substitution and any reordering of Gly, Val, Ser, Trp, Gly, Leu and Arg carries the identical C35H55N11O9 and the identical 773.41842, and only MS/MS with full fragment coverage, or co-elution against a qualified standard, separates them. On a seven-residue peptide with two glycines this is a real synthesis risk and not a theoretical one. (2) leucine/isoleucine substitution: Leu6 to Ile is isobaric at every resolution and is separable only by MS/MS fragmentation behavior or by amino acid analysis, and it is the classic silent substitution when a supplier changes resin lots. (3) C-terminal amide C35H56N12O8, 772.909 / 772.43441 — 0.984 Da below the free acid, and the market conflates free-acid and amide forms of small peptides routinely. (4) tryptophan oxidation at plus 15.995 Da (789.892 / 789.41334) and N-formyl-kynurenine at plus 31.990 Da: the identified degradation pathway on this molecule, visible on the 280 nm channel and nearly invisible on a 214 nm purity number. (5) TRUNCATIONS: des-Arg GVSWGL C29H43N7O8, 617.704 / 617.31731 — the failed final coupling, 156.19 Da light; des-Gly VSWGLR C33H52N10O8, 716.841 / 716.39696 — the failed first coupling, 57.05 Da light. (6) salt axis: acetate as specified, against trifluoroacetate, which is refused because residual trifluoroacetate interferes with the electrophysiology and cell-culture work that is this article's declared laboratory research use; the 1:1 acetate formula unit is 833.945 against 773.893 free peptide, a 7.2 percent content difference. (7) the parent: spadin, PE 12-28, 17 residues, formula from PubChem CID 91826106 as C96H142N26O22, which gives 2012.352 average and 2011.0792 monoisotopic — a different article entirely, 1238.46 Da heavier, and sold under names that overlap this one's. (8) presentation axis: the research-chemical channel sells this article in dose-shaped 8 mg and 10 mg vials marketed for a named human condition; a vial in that format is not received against this specification. (9) channel axis: the institutional article and the research-channel article are separated by a factor of about thirty-two in cost per milligram, and that gap is attributable to characterization rather than to the molecule.

2 Class & testing panel

Form

Single article

Testing panel

P1 — 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 it is entirely non-human. Identifiers and study types only. Mazella et al., PLoS Biol 2010, PMID 20405001 — in vitro binding and electrophysiology plus mouse. Djillani et al., Front Pharmacol 2017;8:643, PMID 28955242 — in vitro patch-clamp on hTREK-1/HEK cells plus mouse behavioral work; this is the paper in which the article was derived and named. Devader et al., Br J Pharmacol 2015, PMID 25598009 — in vitro plus mouse. Moha Ou Maati et al., Neuropharmacology 2012, PMID 21807005 — mouse. Moha ou Maati et al., Brain Struct Funct 2016, PMID 25233810 — mouse. Pietri et al., Neuropharmacology 2019, PMID 31325429 — animal. Wu et al., CNS Neurosci Ther 2021, PMID 32864894 — mouse, genetic and pharmacological. A zebrafish comparative study at PMID 30333618. No human study of PE-22-28 or of spadin of any kind has been identified: every identified publication is in vitro, animal (mouse, rat, zebrafish) or review, and no human has received this article in a published study. The evidence base grades D. No registered human clinical trial was identified. Literature volume by study type is printed at the head of the research page so a reader sees the size of the base before reading a word of it.

4 Storage & specification

Storage

White to off-white lyophilized powder, acetate salt, in amber glass vials with a nitrogen headspace and desiccant; non-sterile, no sterility claim, no stoppered-and-crimped injection format, no dose-shaped vial. -20 degrees C plus or minus 5 degrees C, desiccated, protected from light — amber glass and nitrogen overlay are specification items because the indole side chain is photolabile and oxidation-prone. Equilibrate to room temperature sealed before opening. Reconstituted stock is aliquoted and frozen, and freeze-thaw cycling is avoided. One institutional supplier records solubility to 2 mg/ml in water for its own article, and that figure is that supplier's and is recorded as such. One handling fact is specific to this molecule: at the sub-nanomolar working concentrations used in electrophysiology, adsorptive loss to plastic and glass is a real and measurable problem, so low-binding tubes and a carrier protein in the perfusate are handling requirements rather than refinements. A single excursion to 2-8 degrees C of up to 30 days cumulative is permitted and recorded on the lot record.

Shelf life

The retest interval is 24 months at -20 degrees C plus or minus 5 degrees C, supported by this company's own three-lot ICH Q1A-format study — long-term at -20 degrees C, accelerated at 25 degrees C and 60 percent RH, with photostability under ICH Q1B option 2. The stability-indicating attributes are the tryptophan oxidation products at plus 15.995 and plus 31.990 Da, tracked on the 280 nm channel, and not total assay: indole oxidation is the identified pathway and a 214 nm assay barely registers it. Karl Fischer water is trended alongside them. The interval is shortened on data and never extended without a completed dataset.