Antimicrobial peptides are a potential new generation of drugs that are extremely diverse and could help to fight the imminent threat of antibiotic resistant bacteria. In this study, we attempt to determine the octanol:water partition coefficient for the antimicrobial peptides indolicidin (amino acid sequence: ILPWKWPWWPWRR-NH2) and its derivative indolicidin45 to better understand their potential mechanisms of action when attacking pathogens. The partition coefficient is defined as the ratio of concentrations of a solute in two immiscible liquids at equilibrium. It helps determine the hydrophobicity/hydrophilicity of an analyte. Indolicidin45 has its fourth and fifth highly hydrophobic tryptophan residues relative to the N-terminus swapped with less hydrophobic alanines. This reduced the cytotoxicity while increasing the bioactivity of the derived molecule. Capillary electrophoresis is the instrument that separates analytes based on their relative electrophoretic mobilities and was used for this study. Micellar electrokinetic chromatography is a technique done with capillary electrophoresis which can help to determine the capacity factors and partition coefficients of the peptides for this study. This technique utilizes micelles as a pseudo-stationary phase; the analyte can then partition between the micelles and the aqueous buffer running through the capillary. The capacity factor of the peptides was first needed in order to determine the partition coefficients. The capacity factors of indolicidin and indolicidin45 were determined to be 0.21 +/- 0.04 and 0.23 +/- 0.04, respectively. From these values the partition coefficients were estimated based off a Log P vs. Log k’ calibration curve of known values. The log of the partition coefficients for indolicidin and indolicidin45 were determined to be 1.55 ± 0.04 and 1.62 ± 0.04, respectively. Since these Log P values seen are greater than 1, they suggest that both peptides are hydrophobic. As a result, a potential mode of action for these AMPs to kill pathogens may be to bind and disrupt/lyse the microbial membrane leading to cell death. As potential drugs, this is also promising as it is important that they would be able to cross the bacterial cell membrane to attack pathogens which more hydrophilic molecules cannot do. Some future directions would be to determine the partition coefficient but with the vesicular electrokinetic chromatography method as well as looking into other derivatives of indolicidin for better potential to one day be used as drugs to fight against antibiotic resistant bacteria.
