Catalogue / LL-37
LL-37
Also written as Cathelicidin antimicrobial peptide, CAP-18 fragment.
A 37 residue cationic antimicrobial peptide, the only human cathelicidin, and at nearly 4.5 kilodaltons a genuinely difficult synthesis.
| Molecular formula | C205H340N60O53 |
| Average mass | 4493.26 Da |
| Monoisotopic mass | 4490.5754 Da |
| Residues | 37 |
| Termini | C-terminal free acid |
| Class | Signalling and mitochondrial peptides |
| Determination | Peptide analysis, specialist compound |
| Price | 590 USD |
Computed at build time from the composition shown on this page, not transcribed from a supplier datasheet.
LL-37 has an average molecular weight of 4493.26 daltons and a monoisotopic mass of 4490.5754 daltons. Identity is confirmed by matching the measured deconvoluted mass to that figure, and purity is reported separately by reversed-phase chromatography at 214 nm. The two numbers answer different questions and neither substitutes for the other.
| One letter | LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES |
| Three letter | 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 |
| Modifications | C-terminal free acid |
The formula and both masses in the table above are derived from this sequence and these terminal modifications. A reader who believes a figure is wrong can check the composition rather than take the number on trust, which is the point of publishing it this way.
A sequence is not an identity result. It is the expected composition against which a measured mass is compared, and the comparison is what appears on the certificate.
| Charge | m/z |
|---|---|
| [M+3H]3+ | 1497.866 |
| [M+4H]4+ | 1123.651 |
| [M+5H]5+ | 899.122 |
These are the ions an electrospray source is expected to produce for a neutral mass of 4490.5754 daltons, computed from the monoisotopic mass and the proton mass. They are what a raw spectrum should show before deconvolution.
A report that gives only a deconvoluted mass without the charge states it was derived from cannot be checked. Deconvolution is a calculation, and a calculation whose inputs are not shown is an assertion.
| Thirty-seven residues of solid phase synthesis produce a real population of deletion sequences. Purity in the low nineties is normal for honest material and a claim of 99 percent deserves the chromatogram. |
| Eleven basic residues make the peptide highly charged, so the electrospray envelope spreads across many states and deconvolution is mandatory. |
| The peptide is antimicrobial by design, which interferes with any microbial enumeration performed on the same preparation. Inhibition has to be neutralised and the neutralisation validated. |
Every compound fails in its own way. A generic peptide method applied without regard to these specifics produces a number that looks like a result and is not one.
Endogenous peptides with defined sequences, mostly unmodified, where the analytical question is simply whether the delivered material is the stated sequence at the stated mass.
LC-MS identity with deconvolution and RP-HPLC purity at 214 nm.
Where the delivered milligram figure matters rather than the percentage, net peptide content by combustion analysis and water by Karl Fischer are added, and the certificate carries a closed mass balance instead of a single purity number.
| LC-MS identity | Measured mass |
| RP-HPLC purity | Area at 214 nm |
| Net peptide content | Milligrams |
| Water content | Karl Fischer |
| Counter-ion | Ion chromatography |
| Bacterial endotoxins | USP <85> |
What is the molecular weight of LL-37?
The average molecular weight is 4493.26 daltons and the monoisotopic mass is 4490.5754 daltons, computed from the sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES shown on this page. Both figures are calculated rather than transcribed, so they can be checked against the stated composition.
How is LL-37 tested for purity and identity?
LC-MS identity with deconvolution and RP-HPLC purity at 214 nm. Purity describes the chromatographable fraction only and is not the same quantity as the peptide mass delivered per vial.
What goes wrong when LL-37 is analysed?
Thirty-seven residues of solid phase synthesis produce a real population of deletion sequences. Purity in the low nineties is normal for honest material and a claim of 99 percent deserves the chromatogram.
What does LL-37 analysis cost at ANALYTON?
Peptide analysis, specialist compound is priced at 590 US dollars, covering the determinations described on this page. Content, safety and elemental determinations are ordered alongside and are priced separately on the price list.
Other compounds in this class
Updated 2026-09-01. Masses computed at build, not transcribed.