ENHANCED ANTIMICROBIAL ACTION OF LYSOZYME AGAINST GRAM-NEGATIVE AND GRAM-POSITIVE BACTERIA DUE TO MODIFICATION WITH PERILLALDEHYDE

Hen egg white lysozyme was covalently modified to various degrees with perillaldehyde, a major phenolic aldehyde in the steam distillate of the green leaves of Japanese shiso [Perilla frutescens (Labiatae)], via Schiff base formation followed by reduction with sodium borohydride. Free amino group determinations revealed three lysozyme derivatives, designated LPa(1), LPa(2) and LPa(4), which contain 0.5, 2.4, and 3.9 residues of perillaldehyde, respectively. These modifications had no dramatic effect on the solubility of the lysozyme derivatives. The lytic activity of the modified lysozymes against Micrococcus lysodeikticus was slightly decreased as the degree of modification increased, but even LPa(4) retained 73% of the activity of the unmodified lysozyme. Fluorescence spectra revealed some conformational changes associated with derivatization of lysozyme with perillaldehyde. Lysozyme modified with four perillaldehyde residues exerted a markedly enhanced antimicrobial activity against both Gram-negative bacteria (Escherichia coli K12) and Gram-positive bacteria (Staphylococcus aureus) compared to the activity of perillaldehyde or lysozyme alone or even their mixtures when examined at the same mole basis. The present approach strongly suggests that the perillaldehyde-lysozyme conjugate can be of value as a novel bactericidal agent in formulated drug or food systems. This approach also, suggests that the catalytic function of lysozyme may be utilized in the development of new therapies or food preservatives by conjugating the molecule with antibacterial compounds which cannot be used alone as food ingredients.