A short peptide, composed of 12 amino acids (EFVFVAHAVPVM), presenting a strongly hydrophobic character, was recently isolated from Lactobacillus gasseri supernatant (AMP12). This peptide has shown antimicrobial activity and may also bind the TLR4 receptor or lipopolysaccharides (LPS), which can result in blocking the activation of the inflammatory pathway. AMP12 was also hypothesized to penetrate into the cell given its small size and its character strongly hydrophobic. We are interested in the characterization of the interaction between AMP12 and lipid bilayers as mimics of the bacterial membrane. NR measurements can provide unique information on the mechanism of action of AMP12. We propose to characterize asymmetric lipid bilayers containing LPS from Escherichia Coli to investigate the location of AMP12 with respect to the bilayer.