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Molecular Weight
Purity
Storage
Appearance
Solubility
01
LL-37 is the only cathelicidin antimicrobial peptide in humans. It is the 37-residue C-terminal fragment released from the precursor protein hCAP18 (human cationic antimicrobial protein, 18 kDa), and is named for its two N-terminal leucines and its length.
It is found in neutrophils and in many epithelial and immune cells, and is one of the most widely studied antimicrobial peptides, with research covering antimicrobial activity, interactions with membranes and innate immune signalling. The material here is a synthetic version of the native sequence, supplied as a lyophilized reference compound for in vitro research only.
02
LL-37 is a cationic peptide that becomes a helix on contact with membranes.
Sequence
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, with free termini.
Charge
Six lysines and five arginines against five acidic residues give a net charge of about +6 at neutral pH.
Amphipathic helix
In water LL-37 is largely unstructured, but in membrane-like environments (lipid bilayers, detergent micelles, trifluoroethanol) it forms an α-helix with hydrophobic residues such as Phe5, Phe6, Ile13, Phe17, Ile20, Phe27, Leu31 and Val32 on one face and charged residues on the other.
No aromatic absorbance at 280 nm
The four phenylalanines absorb weakly near 257 nm, but there is no tryptophan or tyrosine, so absorbance at 280 nm is negligible.
Sensitive residues
Gln22 and Asn30 can deamidate. There is no cysteine or methionine.
03
In vitro research on LL-37 covers three main areas.
Antimicrobial activity
Broth microdilution assays report activity against Gram-positive and Gram-negative bacteria and some fungi, with minimum inhibitory concentrations commonly in the low micromolar range. Activity is strongly affected by salt, divalent cations and serum in the test medium.
Membrane interactions
Studies with model membranes describe both pore-forming (toroidal pore) and membrane-disrupting (carpet-like) mechanisms, depending on peptide concentration and lipid composition.
Immune signalling
Cell-culture work has examined effects on chemotaxis and cytokine production in monocytes and macrophages, including through the formyl peptide receptor FPR2, and its ability to bind bacterial lipopolysaccharide.
These findings are cited as research context only; no effects are claimed for this material.
04
Antimicrobial susceptibility testing
A well-characterised positive control in broth microdilution assays against bacterial and fungal panels.
Membrane biophysics
Used in dye-leakage assays with lipid vesicles, supported bilayer imaging and binding studies.
Structural studies
A standard peptide for circular dichroism and NMR studies of membrane-induced helix formation.
Innate immunity
Applied to monocyte and macrophage cultures in chemotaxis, cytokine and LPS-neutralisation assays.
05
Storage
Store the lyophilized powder at −20 °C, sealed and desiccated.
Reconstitution
Soluble in water, dilute acetic acid or near-neutral buffer; DMSO can be used for concentrated stocks. Swirl gently.
Self-association
LL-37 can form oligomers at micromolar concentrations in solution, which may affect assay results. Dynamic light scattering can be used to check concentrated stocks.
Surface adsorption
Its cationic, amphipathic character makes it stick strongly to glass and untreated plastics. Use low-binding polypropylene, and consider a low concentration of a non-ionic detergent or carrier protein where compatible with the assay.
Solutions
Freeze single-use aliquots and avoid repeated freeze–thaw cycles.
06
LL-37 needs methods suited to mid-sized, cationic, amphipathic peptides.
HPLC
Reversed-phase C18 or C8 with 0.1% TFA. Its tendency to fold and self-associate can broaden peaks; elevated column temperature (about 40–60 °C) usually improves peak shape. Detect at 214 nm.
Mass spectrometry
ESI gives a series of multiply charged ions, commonly +5 to +7 (around m/z 899.7, 749.9 and 642.9 by average mass), which deconvolute to about 4493.3 Da. MS/MS (CID, HCD or ETD) provides sequence coverage.
Circular dichroism
A quick structural check: random coil in buffer, and a helical spectrum with minima near 208 and 222 nm in membrane-mimetic conditions such as trifluoroethanol or SDS.
Impurity profile
Typical checks include deletion and truncated sequences, Gln22/Asn30 deamidation and counter-ion content.
07
LL-37 is the active C-terminal fragment of hCAP18, the only human cathelicidin protein. It is released when hCAP18 is cleaved by proteases.
In water its charged and hydrophobic residues have no reason to organise, so it is mostly unstructured. At a membrane surface, forming an amphipathic α-helix lets its hydrophobic face contact lipids and its charged face stay in water, so the helix becomes favourable.
Published assays report activity against Gram-positive bacteria such as Staphylococcus aureus, Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa, and some fungi such as Candida albicans. Reported values vary widely with test conditions.
It contains no tryptophan or tyrosine, the residues mainly responsible for absorbance at 280 nm. Its phenylalanines absorb only weakly near 257 nm, so quantification uses 214 nm or a peptide-content method.
Physiological salt, divalent cations such as Mg²⁺ and Ca²⁺, and serum proteins reduce LL-37 activity in vitro, mainly by weakening its electrostatic attraction to microbial membranes. Assays in low-salt media therefore show much lower MIC values than those in standard broth, so the medium must always be reported.
No. It is supplied strictly as a reference compound for laboratory and analytical research and is not for human or animal use.
LL-37 Research Reference. (2026). Pure Peptides Labs Research Catalogue. Retrieved from https://purepeptideslabs.net/research-catalogue/cellular-research-peptides/ll-37/
Materials listed on this platform are supported by independent testing and published documentation for laboratory research contexts.
