LL-37

1 Identity

Antimicrobial and immunomodulatory peptides. A 37-residue synthetic peptide corresponding to a human cathelicidin sequence. Made by solid-phase chemical synthesis; not isolated from human material, and no human or animal source material is involved at any stage. and ropocamptide. Two CAS numbers are in commercial circulation for one molecule: 154947-66-7, printed by four sellers, and 597562-32-8, printed by one. A buyer checking CAS against CAS will see a mismatch where none exists chemically.

Sequence

H-Leu-Leu-Gly-Asp-Phe-Phe-Arg-Lys-Ser-Lys-Glu-Lys-Ile-Gly-Lys-Glu-Phe-Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg-Asn-Leu-Val-Pro-Arg-Thr-Glu-Ser-OH; one-letter LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, 37 residues, free acid. All-L, entirely proteinogenic, free N-terminal alpha-amine, free C-terminal carboxylic acid, no amidation, no acylation, no lipidation, no PEGylation. Three compositional facts govern how this article is tested and stored and each is stated rather than inferred. No cysteine, so no disulfide and no scrambling risk. No methionine, no tryptophan and no tyrosine, so there is no classically oxidation-labile residue — the general assumption that a long peptide needs oxidation controls does not hold for this sequence, and the absence of an oxidation panel on its certificate is not a defect. Eleven basic residues (six Lys, five Arg) against five acidic (three Glu, two Asp) and no histidine, giving a net charge near +6 at neutral pH on a strongly amphipathic chain — which makes the molecule adsorptive to glass and plastic and prone to self-association, and makes counterion load a first-order quantity rather than a footnote.

Molecular formula

C205H340N60O53 (free acid). C-terminal amide C205H341N61O52. N-terminally extended fall-39 C217H354N62O55. Fragment KR-12 C71H126N24O16. Scrambled control: C205H340N60O53, identical.

Average mass

4,493.34 Da (C205H340N60O53), from the formula on IUPAC 2021 abridged conventional atomic weights: 4,493.342. That value sits between the two institutional printings in circulation — one institutional supplier prints 4493.32 and another prints 4493.37 — and reconciles with both to within their own rounding. Counterion is not A rounding error on eleven basic residues: a fully trifluoroacetate-exchanged salt carries up to 1,254 Da of trifluoroacetate against 4,493 Da of peptide, 21.8 percent of the vial, and even a six-equivalent load is 13.2 percent. Eleven equivalents of acetate is 660.6 Da. C-terminal amide 4,492.36. FALL-39 4,711.60. KR-12 1,571.94.

Monoisotopic mass

4,490.57543 Da neutral (C205H340N60O53). The practical release measurement is the deconvoluted average mass from a multiply-charged envelope rather than a monoisotopic peak — for example [M+4H]4+ near m/z 1,123.65 or [M+5H]5+ near m/z 899.12 — and the certificate must print the charge states used. C-terminal amide 4,489.59141, i.e. 0.98 Da lighter. Asn30 deamidation gives +0.98 Da, 4,491.56 monoisotopic. FALL-39 4,708.68095. KR-12 1,570.97836. The FALL-39 and KR-12 figures are derived by residue arithmetic from the stated formulas and are not corroborated against any supplier record; that qualification travels with them wherever they are quoted.

Salt / variant note

Six articles trade under or near this name, plus a registry problem and a live error on a sales listing. (1) LL-37 free acid, C205H340N60O53, 4,493.34 average / 4,490.57543 monoisotopic. (2) the two-CAS problem: 154947-66-7 and 597562-32-8 both circulate for this molecule, so an order-to-certificate CAS mismatch is a registry split rather than a substitution — stated plainly so that it is not mistaken for fraud, and so that a real substitution is not excused as one. (3) C-terminal amide C205H341N61O52, 4,492.36 / 4,489.59141 — 0.98 Da lighter than the intended free acid. (4) FALL-39, the N-terminally extended 39-residue form FALLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, C217H354N62O55 = 4,711.60 / 4,708.68095 by residue arithmetic, derived and not corroborated against any supplier record — +218.26 Da, and it appears in the literature under a name adjacent to this one. (5) KR-12, the LL-37(18-29) fragment KRIVQRIKDFLR, C71H126N24O16 = 1,571.94 / 1,570.97836, also derived by the same arithmetic — a widely sold short analog at roughly a third of the mass. (6) scrambled LL-37, a sequence-shuffled control peptide sold as a research reagent: identical formula, identical mass to every decimal place, identical amino acid analysis, and distinguishable only by MS/MS sequencing. (7) Counterion forms across up to eleven equivalents of acetate or trifluoroacetate, moving gross fill weight by up to 22 percent. (8) Asn30-deamidated species, +0.98 Da, and the Asp4 and Asp26 succinimide and iso-Asp species, which are isobaric with the parent. A live error on A sales listing, carried here because it is the reason the arithmetic check exists: one seller prints the formula for its LL-37 product as C205H340N50O53 — N50 rather than N60 — which computes to 4,353.27 Da, 140.07 Da below the mass printed on the same page. That is a transcription error on a live listing and it is exactly the class of error a certificate check by arithmetic catches before a lot is accepted.

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 is large but lopsided, and the shape matters more than the volume. In-vitro and immunology literature on the cathelicidin runs to a few thousand primary reports covering antimicrobial screening panels, structural biology, membrane biophysics and tissue expression, plus a substantial rodent-model file. Human interventional evidence is limited: a small number of early-phase topical wound studies of the synthetic peptide, sponsored by its originator, Promore Pharma, under the name ropocamptide; no Phase 3 dataset; and no product approved in any jurisdiction. The great majority of the human data are observational expression studies measuring endogenous cathelicidin in tissue rather than interventional studies of exogenous peptide, and the citation index labels each entry with its study type so that the volume of the literature is not mistaken for the weight of it.

4 Storage & specification

Storage

White to off-white lyophilized powder, acetate salt, in a screw-cap amber borosilicate vial with a PTFE-lined closure; a laboratory-chemical presentation, non-sterile, with no sterility claim. Two presentations are offered, a 5 mg vial and a 25 mg vial. Store at -20 degrees C plus or minus 5 degrees C, desiccated and protected from light, with -80 degrees C specified for holds beyond twelve months. The handling fact that governs this record is adsorption rather than chemistry: the peptide is strongly cationic and amphipathic and will plate out onto ordinary borosilicate and polypropylene at low concentration, which is a source of apparent low recovery in the buyer's own assay as much as in this laboratory's, so the container-closure is part of the specification and low-adsorption or pre-passivated vessels are specified for dilute work. Vials are equilibrated to ambient temperature before opening. Reconstituted solution is aliquoted single-use and held at -80 degrees C; self-association at higher concentration makes repeated freeze-thaw a real rather than a nominal risk on this molecule. Oxidation is not the governing degradation route on this sequence: deamidation, aspartate isomerization, chain-length impurities and adsorption are, and each carries its own specified limit rather than being pooled.

Shelf life

Provisional retest interval 18 months from QA release at -20 degrees C plus or minus 5 degrees C, desiccated — deliberately shorter than the 24 months assigned to the short peptides in this catalog, because a 37-mer has more available degradation routes and a thinner margin against a 95.0 percent purity limit. Provisional pending the company's own stability data on the first three commercial lots under an ICH Q1A(R2)-style protocol: 12 months real time with pulls at 0, 3, 6, 9 and 12 months at the labeled condition, plus 6 months accelerated at 40 degrees C / 75 percent relative humidity, with the deamidated and isomerized species reported individually at every pull rather than pooled into total related substances. Extension to 24 months is permitted only on twelve months of completed real-time data at the labeled condition from three lots. A retest date is printed on every vial and first-expiry-first-out is enforced against that date.