N-Formyl-Met-Leu-Phe (fMLF)

Also known as fMLF; fMLP; N-formylmethionyl-leucyl-phenylalanine

An N-formylated tripeptide used to probe FPR1 signalling, neutrophil chemotaxis and oxidative burst in experimental systems.

Length: 3 amino acids
Half-life: Not well characterised
Mechanism: fMLF activates formyl peptide receptor 1 (FPR1), a Gi-coupled receptor, initiating calcium mobilisation, phosphoinositide signalling and downstream responses such as chemotaxis and oxidative burst. Activity at other formyl peptide receptors depends on concentration and species, so it is not universally receptor-selective.
Studied in: Laboratory studies use fMLF in isolated neutrophils, differentiated myeloid cell lines, receptor-transfected cells and animal inflammation models to examine formyl peptide sensing and leukocyte recruitment.

About N-Formyl-Met-Leu-Phe (fMLF)

N-Formyl-Met-Leu-Phe consists of methionine, leucine and phenylalanine, with a formyl group attached to the amino-terminal methionine. Its conventional structure is formyl-L-Met-L-Leu-L-Phe with a free carboxyl terminus. Work on bacterial chemotactic factors in the 1970s established short N-formylated peptides as potent leukocyte stimuli. The formylated terminus reflects a feature of bacterial and mitochondrial protein synthesis, making fMLF a defined experimental probe of innate recognition rather than a full-length host defence peptide.

FPR1 is the principal high-affinity receptor target in commonly used human neutrophil assays. Receptor activation couples to Gi proteins and engages pathways controlling calcium flux, actin rearrangement, granule release and NADPH oxidase activity. Researchers separate these responses using migration chambers, fluorescence-based calcium measurements and reactive oxygen species assays. Interpretation requires attention to receptor expression and species: mouse formyl peptide receptor pharmacology does not precisely reproduce that of human FPR1, and prolonged stimulation can produce receptor desensitisation.

Laboratory notes

Check the certificate of analysis for N-terminal formylation, stereochemistry and terminal chemistry; unformylated Met-Leu-Phe is not an equivalent assay reagent.
Choose a solvent compatible with the supplied material and assay, and include a matched vehicle control because solvent carry-over can alter leukocyte responses.
Use freshly prepared working dilutions where practical, minimise repeated freeze–thaw cycles and assess methionine oxidation when investigating unexpected changes in activity.

Storage and reconstitution basics: storage guide.

Questions about N-Formyl-Met-Leu-Phe (fMLF)

Do fMLF and fMLP refer to different peptides?

They commonly denote the same tripeptide. fMLF uses the one-letter amino acid code, whereas fMLP is an older abbreviation in which P represents phenylalanine rather than proline.

Is fMLF an FPR1-specific probe in every assay?

No. FPR1 is its principal high-affinity target in human neutrophils, but concentration, species and expression of other formyl peptide receptors influence selectivity. Receptor-deficient cells or complementary pharmacological controls help establish target involvement.

Can a calcium response establish chemotaxis?

No. Calcium mobilisation demonstrates a signalling response, whereas chemotaxis requires directional migration along a gradient. A migration assay with appropriate gradient controls is needed to distinguish chemotaxis from non-directional movement.

Is N-Formyl-Met-Leu-Phe (fMLF) for human use?

No. It is supplied strictly for in-vitro laboratory research and is not for human or animal consumption.

Related research peptides

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