LL-37 is a descriptive shorthand, not a chemical name. This page sets out the identity of LL-37: what the sequence is, what mass to expect, how it behaves under reverse-phase HPLC, and how a buyer can confirm that the material in a vial is what the label says. It is silent on what LL-37 does, and it contains no guidance on preparation, handling or dosing.
The sequence behind LL-37
LL-37 is a 37-residue linear peptide with the sequence:
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
All thirty-seven residues are standard L-amino acids. The common synthetic form has a free N-terminal amine and a free C-terminal acid, and the sequence contains no cysteine, so there are no disulfide bonds. The molecular formula is C205H340N60O53 and the average molecular mass is approximately 4493.3 g/mol.
At this size the composition is worth summarising, because it drives everything about the analytical behaviour. The sequence contains six lysines and five arginines (eleven basic residues) against two aspartic acids and three glutamic acids (five acidic residues), giving a net charge of about +6 at neutral pH. It also contains four phenylalanines and a run of leucines, isoleucines and valines, and it has no tryptophan or tyrosine.
What the name LL-37 refers to
The name is a literal description: the peptide begins with two leucines (LL) and is 37 residues long. It corresponds to the C-terminal segment of the human cathelicidin precursor protein, hCAP18, and in the UniProt record for that precursor it occupies residues 134 to 170. Other fragments of the same precursor, shorter or longer, circulate under their own names and are different compounds.
Because the name is only a starting pair and a length, it is easy for a truncated or extended variant to be labelled LL-37. A 36-mer missing one terminal residue, or a sequence with a single substitution, would still “start with LL” and sit within a few percent of the same mass. The full printed sequence is the identifier; the name is not.
How a cationic, amphipathic 37-mer behaves on reverse-phase HPLC
LL-37 is strongly amphipathic: when drawn as a helix, its hydrophobic residues line up along one face and its charged residues along the other. That structure makes it one of the more demanding peptides in a research catalogue to chromatograph well.
- Retention is strong. The hydrophobic face interacts firmly with a C18 phase, so LL-37 elutes late in a standard water/acetonitrile gradient, at a considerably higher organic percentage than the short peptides in this series.
- Peak shape can suffer. The many basic residues can interact with residual silanols on the column, producing tailing. Adequate ion-pairing (trifluoroacetic acid at a consistent concentration) and a wide-pore column (often 300 Å, C4, C8 or C18) usually give sharper peaks.
- Adsorption and aggregation matter. Amphipathic cationic peptides stick to glass and some plastics and can self-associate, so apparent losses of material or broad, split peaks can reflect sample behaviour rather than impurity.
On detection, LL-37 has no tryptophan or tyrosine. Its four phenylalanines absorb weakly and at a shorter wavelength, so absorbance at 280 nm is minimal and purity has to be read on the peptide bond at around 214 nm.
What an analysis for LL-37 should show
A useful certificate reports the column chemistry, pore size and dimensions, mobile phases and gradient, detection wavelength, retention time, the integrated main peak with its integration window visible, and a mass confirmation. For a 4.5 kDa peptide, electrospray mass spectrometry shows a series of multiply charged ions, and the deconvoluted mass should land at or near 4493.3 for the free peptide. Our article on mass spectrometry and peptide identity explains how that deconvolution works.
Long sequences carry more synthesis-related impurities than short ones. Deletion sequences (a single missing residue) are the most important, because they can co-elute closely with the full-length peptide and differ in mass by only one residue. A certificate that pairs the chromatogram with a mass spectrum is far more informative than retention time alone. See peptide synthesis impurities for the common types.
For LL-37, chromatographic purity and net peptide content should be two distinct entries, with the counter-ion stated. With eleven basic side chains plus the N-terminal amine, a trifluoroacetate salt of LL-37 carries a large number of counter-ions per molecule, and bound water adds further mass. The net peptide content figure is what tells you how much of the weighed powder is peptide. Our explainer on peptide purity vs net peptide content covers the difference.
Confirming identity independently
Query databases with the LL-37 sequence instead of the designation. The human cathelicidin precursor is indexed in public protein databases, and LL-37 appears there as an annotated segment of it; chemical databases also list the free peptide by formula. Checking that a vendor’s sequence matches residues 134 to 170 of the precursor, letter for letter, is the quickest way to rule out a truncated or substituted variant. The LL-37 product page links straight to those database entries.
How LL-37 is supplied here
LL-37 5mg is supplied as a lyophilised powder in a sealed vial. LL-37 carries its own published reverse-phase HPLC result from an independent laboratory. You will find the LL-37 vial size and its published HPLC purity on the product page. LL-37 vials are not lot-numbered; the crimp and cap color identify which published analysis it belongs to.
Frequently asked questions
What is the amino acid sequence of LL-37?
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, thirty-seven standard L-amino acids with a free N-terminus and a free C-terminal acid.
Why is it called LL-37?
Because the sequence starts with two leucines and is thirty-seven residues long. The name describes the sequence; it is not a systematic identifier.
What molecular weight should I expect for LL-37?
Approximately 4493.3 g/mol for the free peptide, formula C205H340N60O53. The salt form of LL-37 carries extra mass, which is why the counter-ion belongs beside the number.
Why does LL-37 elute so late compared with short peptides?
Its hydrophobic face, with four phenylalanines and several leucines, isoleucines and valines, binds strongly to a reverse-phase column. Late elution at a high organic percentage is expected for this compound.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.