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