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)], vi a 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 d ramatic effect on the solubility of the lysozyme derivatives. The lyti c activity of the modified lysozymes against Micrococcus lysodeikticus was slightly decreased as the degree of modification increased, but e ven LPa(4) retained 73% of the activity of the unmodified lysozyme. Fl uorescence spectra revealed some conformational changes associated wit h derivatization of lysozyme with perillaldehyde. Lysozyme modified wi th four perillaldehyde residues exerted a markedly enhanced antimicrob ial activity against both Gram-negative bacteria (Escherichia coli K12 ) and Gram-positive bacteria (Staphylococcus aureus) compared to the a ctivity of perillaldehyde or lysozyme alone or even their mixtures whe n examined at the same mole basis. The present approach strongly sugge sts that the perillaldehyde-lysozyme conjugate can be of value as a no vel bactericidal agent in formulated drug or food systems. This approa ch also, suggests that the catalytic function of lysozyme may be utili zed in the development of new therapies or food preservatives by conju gating the molecule with antibacterial compounds which cannot be used alone as food ingredients.