peptide identity FAQ

No. Mouse models should use mouse CRAMP peptide, not human LL-37, unless the research question specifically examines human peptide pharmacokinetics in a murine system. Mouse and human cathelicidins have different receptor binding profiles, tissue distribution, and proteolytic stability. Human LL-37 injected into mice will produce some antimicrobial effects via direct membrane disruption, but immunomodulatory signaling through FPR2 and EGFR will not replicate human responses because murine receptor orthologs have lower binding affinity for the human peptide sequence. If your experimental goal is to model human LL-37 immune function, use human cell assays or humanized mouse models. Wild-type mouse studies require mouse CRAMP for physiological relevance.

Yes. Purity directly affects reproducibility and dose-response accuracy in immune signaling studies. A 95% pure LL-37 preparation contains up to 5% truncated peptides, deletion sequences, or synthesis byproducts that may have different antimicrobial potency or receptor binding affinity. For antimicrobial killing assays where high micromolar doses are used, 95% purity may be acceptable. For receptor signaling studies at nanomolar concentrations (FPR2 calcium flux assays, chemotaxis), impurities at 5% can introduce confounding ligands that skew dose-response curves. Research-grade LL-37 should meet ≥98% purity by HPLC for publication-quality data. This is the standard Real Peptides guarantees, with every batch tested for sequence fidelity and deletion variant contamination before release.

Use human LL-37 unless the protocol explicitly requires the hCAP-18 precursor or a non-human ortholog like mouse CRAMP. The vast majority of published cathelicidin research used the active LL-37 fragment because the precursor has negligible bioactivity in vitro. If replicating a published study, check the methods section for peptide supplier and catalog number. If the original study used a 4–5 kDa peptide, it was LL-37; if 18 kDa, it was hCAP-18. When in doubt, LL-37 is the correct choice for antimicrobial assays, immune cell migration studies, and receptor binding experiments.

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.

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.

Contact your supplier to confirm the exact peptide sequence and species origin. If the supplier documentation lists 'human cathelicidin, active fragment, 37 amino acids,' it is LL-37. If documentation does not specify 'active fragment' or lists molecular weight as 18 kDa, you may have received the inactive hCAP-18 precursor, which will not produce antimicrobial or immunomodulatory effects in standard assays. Request a certificate of analysis showing mass spectrometry confirmation of the 37-amino-acid sequence and N-terminal leucine-leucine residues. This is the definitive verification that cathelicidin same as LL-37 applies to your order.

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.

Verify the CAS registry number and catalog specifications before ordering. If both listings show the same molecular weight (approximately 404 Da), amino acid sequence (Ala-His-Lys), and copper coordination, they are the same peptide and ordering both wastes budget. Contact the supplier directly and request clarification—reputable vendors will confirm the duplication and consolidate the order. If the supplier insists they are different compounds without providing distinguishing analytical data, that's a red flag indicating insufficient quality control or deliberate catalog padding.

Check three variables: peptide concentration, copper coordination, and media composition. Effective concentrations range from 1–50 μM depending on assay endpoint—lower concentrations suit proliferation assays, higher concentrations are used for ECM gene expression studies. Verify the peptide was stored correctly and hasn't exceeded its reconstituted shelf life. Finally, confirm your culture media doesn't contain EDTA or other chelating agents that strip copper from the peptide, rendering it inactive. Switch to EDTA-free media and supplement fresh peptide every 48 hours for extended assays.

Copper-peptide complexes can range from off-white to pale blue depending on copper oxidation state and counterion composition. A blue tint typically indicates Cu²⁺ in a specific coordination geometry and is not inherently problematic. However, reconstitute a small aliquot and measure absorbance at 280 nm (peptide bond) and 600–650 nm (copper d-d transition). If the 600 nm peak is disproportionately high relative to the peptide peak, the sample may contain excess free copper ions. Request a CoA with copper quantification data to confirm the 1:1 peptide-to-copper ratio.