Antimicrobial effects of lysozyme against gram-negative bacteria due to covalent binding of palmitic acid

Chicken lysozyme was chemically modified to various degrees with the N-hydroxysuccinimide ester of palmitic acid. Lytic activity of lysozyme against Micrococcus lysodeikticus was slightly decreased with the increase of attached palmitoyl residues up to two residues per molecule, whereas further modification resulted in unfavorable insolubility and less active lysozyme. Lysozyme derivatives exhibited a substantial antimicrobial activity against Gram-negative bacteria (Escherichia coli wild type 3301) without addition of EDTA or heating. The most potent derivative was the lysozyme incorporating two palmitoyl residues (P2-LZ). Lytic activity of lysozyme derivatives in the presence of purified LPS (outer membrane lipopolysaccharides of E. coli) against M. lysodeikticus was consistently decreased with an increase in the degree of modification with palmitic acid. This suggested that enhanced activity of palmitoyl lysozyme molecules occurred via membrane insertions through the LPS zone. The foam stability and emulsifying activity of lysozyme were markedly promoted in response to the increase in the extent of palmitoylation up to four residues per molecule. Thus, this approach indicates that palmitoyl lysozyme in the formulated food systems would provide a novel class of therapeutic agents and food safety