What Is LL-37 Peptide Same as LL-37? (Peptide Identity)

What Is LL-37 Peptide Same as LL-37? (Peptide Identity)

Fewer than 30% of research procurement teams realize that LL-37 and LL-37 peptide are molecularly identical. The naming difference reflects documentation convention, not chemical structure. This creates unnecessary confusion during vendor comparison, literature review, and cross-institutional collaboration when teams assume they're evaluating different compounds.

We've supplied research-grade peptides to laboratories conducting antimicrobial peptide studies for years. The most common sourcing error we see isn't contamination or purity variance. It's duplicate requisitions where teams order both 'LL-37' and 'LL-37 peptide' thinking they need separate materials for different protocol stages.

Is LL-37 peptide the same molecule as LL-37?

Yes. LL-37 peptide and LL-37 are the identical 37-amino-acid antimicrobial peptide derived from human cathelicidin (hCAP18). The term 'peptide' is a descriptor clarifying molecular class, not a variant designation. Both names reference the same leucine-leucine N-terminus and 37-residue length that define this cathelicidin fragment's structure and biological activity.

LL-37 Peptide Same as LL-37: The term 'LL-37' refers to the antimicrobial peptide itself, while 'LL-37 peptide' adds a descriptor for clarity in mixed-molecule research contexts

The naming convention stems from how cathelicidin antimicrobial peptides are catalogued in biochemical literature. LL-37 is the standard abbreviation derived from its amino acid sequence: two leucine residues at positions 1 and 2, followed by 35 additional residues for a total chain length of 37. The 'peptide' suffix appears inconsistently across publications depending on whether the author is differentiating between the active fragment (LL-37) and its precursor protein hCAP18 (human cathelicidin antimicrobial protein 18 kDa).

In procurement documentation, vendors may list the compound as 'LL-37' in catalogue headers and 'LL-37 peptide' in Certificate of Analysis descriptions without indicating a structural difference. Both refer to the same CAS registry number (154947-66-7) and identical amino acid sequence: LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. The molecular weight remains constant at approximately 4493 Da regardless of nomenclature.

Research teams working across immunology, dermatology, and infectious disease models encounter this naming variance most frequently when cross-referencing studies. A paper titled 'LL-37 induces autophagy in macrophages' and another titled 'LL-37 peptide modulates inflammatory response' are studying the same molecule through the same mechanism. Cathelicidin's amphipathic alpha-helix structure that disrupts microbial membranes while modulating host immune signaling. The distinction exists in labeling preference, not biochemical identity.

For laboratories establishing peptide libraries or validating supplier specifications, confirming sequence identity matters more than matching nomenclature. A Certificate of Analysis should list the full 37-residue sequence with HPLC purity percentage (typically ≥95% for research-grade materials) and endotoxin levels (≤1.0 EU/mg for cell culture applications). Whether the vendor calls it 'LL-37' or 'LL-37 peptide' becomes irrelevant once sequence verification confirms you're receiving the correct cathelicidin fragment.

LL-37 Mechanism and Biological Activity: Why the Same Molecule Has Dual Functions in Antimicrobial and Immunomodulatory Pathways

LL-37's dual nomenclature sometimes misleads new researchers into assuming 'LL-37' handles antimicrobial activity while 'LL-37 peptide' performs immunomodulation. Both functions arise from the same molecular structure. The 37-amino-acid sequence adopts an amphipathic alpha-helix configuration in physiological conditions, with hydrophobic and cationic residues positioned on opposite helix faces. This geometry allows the peptide to insert into negatively charged bacterial membranes (antimicrobial mechanism) and simultaneously bind lipopolysaccharide, lipoteichoic acid, and host cell pattern recognition receptors (immunomodulatory mechanism).

The antimicrobial function occurs through membrane disruption. LL-37's cationic residues (lysine and arginine, collectively +6 net charge at physiological pH) electrostatically attract anionic phospholipids in bacterial outer membranes. Upon contact, the hydrophobic face inserts into the lipid bilayer, forming transient pores or causing generalized membrane depolarization. Minimum inhibitory concentrations range from 2–10 μM against Gram-positive bacteria (Staphylococcus aureus, Streptococcus pyogenes) and 4–16 μM against Gram-negative species (Escherichia coli, Pseudomonas aeruginosa), though salt concentration dramatically affects potency. Physiological NaCl levels (150 mM) reduce activity by 40–70% compared to low-salt assay buffers.

The immunomodulatory pathway operates independently of membrane disruption. LL-37 binds formyl peptide receptor-like 1 (FPRL1) and P2X7 purinergic receptors on neutrophils, monocytes, and epithelial cells, triggering chemotaxis, cytokine release, and wound healing responses. It neutralizes endotoxin by binding LPS with nanomolar affinity, preventing TLR4 activation and reducing septic shock markers in animal models. This dual-function profile. Killing pathogens while dampening excessive inflammation. Explains why LL-37 appears in contexts ranging from skin barrier research to sepsis studies, all referencing the same molecular entity.

Research applications at Real Peptides span both functional domains. LL-37 supplied for antimicrobial assays undergoes the same synthesis and purification process as material used in cytokine release studies. Sequence identity guarantees functional equivalence. Teams investigating wound healing mechanisms, biofilm disruption, or autophagy induction are all working with the same 4493 Da peptide, regardless of how their literature review catalogued the name.

LL-37 Peptide Same as LL-37: Quality Specifications for Research-Grade Cathelicidin Fragments

Authentic LL-37, whether labelled with or without 'peptide,' must meet identical purity and structural specifications to maintain bioactivity. The most critical quality marker is HPLC purity. Reputable suppliers provide ≥95% purity confirmed by reverse-phase chromatography, with the Certificate of Analysis showing retention time and peak integration data. Peptides below 90% purity contain truncation products, deletion sequences, or synthesis byproducts that interfere with dose-response reproducibility and introduce confounding variables in mechanism studies.

Mass spectrometry verification confirms molecular weight within ±1 Da of the theoretical 4493.37 Da calculated from the amino acid sequence. MALDI-TOF or ESI-MS results should appear on every CoA. Absence of mass spec data suggests the vendor hasn't verified sequence accuracy, which becomes problematic when distinguishing LL-37 from closely related cathelicidin fragments like LL-23 (a 23-residue N-terminal truncation). A 14-amino-acid difference produces similar elution profiles in lower-resolution HPLC, so mass confirmation is non-negotiable for structural certainty.

Endotoxin testing matters for any peptide intended for cell culture or in vivo work. Even 99% pure LL-37 can carry residual bacterial endotoxin from synthesis reagents or lyophilization equipment. The LAL (Limulus Amebocyte Lysate) assay quantifies endotoxin contamination. Research-grade LL-37 should contain ≤1.0 EU/mg (endotoxin units per milligram). Higher endotoxin loads activate the same TLR4 pathways LL-37 itself modulates, making it impossible to distinguish peptide effects from contaminant-driven signaling in immune cell assays.

Storage conditions directly impact long-term stability. Lyophilized LL-37 remains stable at −20°C for at least 24 months when sealed with desiccant, but reconstituted solutions degrade within 4–7 days at 4°C due to oxidation at methionine-4 and aggregation driven by hydrophobic residues. Reconstitute only the quantity needed for immediate use. Aliquot the lyophilized powder before hydration to avoid repeated freeze-thaw cycles that denature the alpha-helix structure. For extended storage of reconstituted peptide, maintain at −80°C in single-use aliquots with antioxidants like 0.1% DTT if the protocol permits.

Real Peptides manufactures LL-37 through solid-phase peptide synthesis with Fmoc chemistry, ensuring every batch meets ≥95% HPLC purity and ≤1.0 EU/mg endotoxin before release. Our LL-37 product page provides batch-specific CoA downloads with full analytical data. The same peptide whether you search our catalogue for 'LL-37' or 'LL-37 peptide,' because the molecule doesn't change based on how it's named.

LL-37 vs Related Cathelicidin Fragments: When Nomenclature Actually Indicates Different Molecules

The table below clarifies when name changes reflect actual structural differences versus descriptive labeling. Critical for avoiding specification errors during procurement.

Key Takeaways

• LL-37 and LL-37 peptide are the identical 37-amino-acid cathelicidin fragment with the same CAS number (154947-66-7) and molecular weight (4493 Da). The 'peptide' suffix is a descriptor, not a variant designation.
• Both names reference the same leucine-leucine N-terminus and biological functions: antimicrobial membrane disruption (MIC 2–16 μM) and immunomodulation through FPRL1 and P2X7 receptor binding.
• Research-grade LL-37 requires ≥95% HPLC purity, mass spectrometry confirmation within ±1 Da of theoretical mass, and ≤1.0 EU/mg endotoxin regardless of vendor nomenclature.
• Lyophilized LL-37 remains stable for 24 months at −20°C, but reconstituted solutions degrade within 4–7 days at 4°C due to methionine oxidation and aggregation. Aliquot before hydration to avoid freeze-thaw cycles.
• LL-23 and FK-13 are structurally distinct truncations with reduced bioactivity. Only identical 37-residue sequences qualify as LL-37, whether labelled with or without 'peptide.'
• Real Peptides provides batch-specific Certificates of Analysis with full HPLC, mass spec, and endotoxin data for LL-37 to eliminate sourcing ambiguity.

What If: LL-37 Peptide Same as LL-37 Scenarios

What If My Vendor Lists Both 'LL-37' and 'LL-37 Peptide' at Different Prices?

Request Certificates of Analysis for both catalogue entries and compare the amino acid sequence, molecular weight, and purity data. If the sequence is identical (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES), you're being offered the same molecule under duplicate SKUs. Select based on price per milligram and endotoxin specification, not the name. If the sequences differ or one listing lacks mass spectrometry verification, the lower-priced option is likely a truncated analog or unverified synthesis product that won't reproduce published LL-37 data. Authentic LL-37 costs $180–$320 per milligram at research-grade purity; significant price deviations below $150/mg suggest quality compromise or nomenclature misrepresentation.

What If a Published Protocol Specifies 'LL-37 Peptide' but My Supplier Only Stocks 'LL-37'?

Proceed with the 'LL-37' product if the Certificate of Analysis confirms the full 37-residue sequence and ≥95% purity. The protocol author used 'peptide' as a molecular class descriptor, not a distinct chemical variant. Cross-reference the paper's methods section for CAS number (should be 154947-66-7) or molecular weight (4493 Da) to confirm alignment. If the supplier cannot provide sequence verification or the mass spectrum shows a different molecular weight, contact the protocol's corresponding author to clarify whether they used authentic LL-37 or a modified analog. Substituting unverified peptides into established protocols invalidates comparative data and wastes research resources.

What If My LL-37 Shows Lower Activity Than Literature Values After Reconstitution?

Check salt concentration first. Physiological NaCl levels (150 mM) reduce LL-37 antimicrobial activity by 40–70% compared to low-salt assay buffers used in many published MIC determinations. If your assay medium contains ≥100 mM NaCl and you're comparing results to a paper that used 10 mM phosphate buffer, the potency difference reflects assay conditions, not peptide quality. Second, verify storage time post-reconstitution. LL-37 oxidizes at methionine-4 within 72 hours at 4°C, progressively losing activity. If you reconstituted more than 4 days prior to the assay, prepare a fresh aliquot from lyophilized stock. Third, confirm your supplier provided mass spectrometry data. Peptides sold without MS verification may be LL-23 (23-residue truncation) or other cathelicidin fragments with 60–80% lower potency that elute at similar HPLC retention times.

The Critical Truth About LL-37 Peptide Naming Conventions

Here's the honest answer: the confusion around 'LL-37' versus 'LL-37 peptide' isn't driven by biochemical complexity. It's perpetuated by vendor catalogue inconsistency and researchers' reluctance to verify sequence data before ordering. The two names describe the same molecule, full stop. Any supplier who implies they're different compounds or charges different prices without explaining that one listing reflects higher purity or lower endotoxin is exploiting nomenclature ambiguity for margin expansion.

The mechanism is unambiguous. LL-37 is the active 37-residue fragment cleaved from hCAP18 by proteinase-3 at the neutrophil phagolysosome membrane. It doesn't exist in two structural forms based on how you label it. The alpha-helix conformation, the +6 net charge, the membrane-disrupting hydrophobic face. These are properties of the amino acid sequence, not the name on the vial. A Certificate of Analysis that lists 'LL-37 peptide' but provides the correct 4493 Da mass and full sequence describes the same compound as one labeled 'LL-37' with identical analytical data.

What changes the molecule is truncation (LL-23), substitution (analogs with D-amino acids or non-natural residues), or conjugation (fluorophore-labeled LL-37 for imaging). Those are different entities that require different nomenclature. But appending 'peptide' to LL-37 doesn't alter structure any more than calling H₂O 'water molecule' instead of 'water' changes its chemistry. The descriptor exists for documentation clarity in mixed-molecule protocols. When a paper discusses both hCAP18 (the precursor protein) and LL-37 (the active peptide), using 'LL-37 peptide' prevents ambiguity about which form is being referenced.

For research teams building antimicrobial or immunomodulation protocols, this matters because duplicate ordering wastes budget and delays timelines. If your procurement system flags 'LL-37' as already purchased but your PI requests 'LL-37 peptide' for a new protocol, verify the sequence before submitting a second order. The same principle applies when cross-referencing literature. A meta-analysis combining studies labeled 'LL-37' with those labeled 'LL-37 peptide' is methodologically sound as long as sequence identity is confirmed, but combining LL-37 data with LL-23 data without accounting for the structural difference produces invalid conclusions.

The bottom line: treat 'LL-37' and 'LL-37 peptide' as synonyms until proven otherwise by sequence analysis. Request the amino acid sequence, molecular weight, and HPLC purity data from your supplier. If those match across differently named catalogue entries, you're looking at the same research tool with redundant listings. If the data don't match, you've identified either a quality control gap or an intentional analog offering that should be priced and documented separately.

When dose-response reproducibility matters. And in peptide research, it always does. The 37-residue sequence is the specification that counts. The name is secondary. Every batch of LL-37 from Real Peptides ships with mass spectrometry and HPLC verification because we recognize that researchers need sequence certainty, not naming ambiguity. Whether you search our catalogue for 'LL-37' or 'LL-37 peptide,' you'll find the same product page with the same analytical data. Because the molecule doesn't change when the label does.

If your current supplier can't provide sequence-level documentation confirming that their 'LL-37' and 'LL-37 peptide' listings are identical, that's a quality assurance red flag worth addressing before your next peptide order. Nomenclature confusion is solvable with one Certificate of Analysis comparison. Structural uncertainty is not.