A Structural Phase of Heat-Denatured Lysozyme with Novel Antimicrobial Action

The structure and antimicrobial function of hen egg white lysozyme was investigated by means of thermal denaturation at 80 °C (pH 7.2), which leads to irreversible denaturation. With an increase in the heating time (up to 30 min) of lysozyme, the soluble fraction showed progressive decrease in its enzyme activity that coincided with the formation of a slower migrating band on the acid PAGE. Fluorescence spectra revealed that, as the extent of denaturation increases, the surface hydrophobicity and the exposure of tryptophan residues were greatly promoted. In parallel to these conformational changes of lysozyme there has been consistent increase in its antimicrobial activities against Gram-negative bacteria, with no detrimental effect on its inherent action to Gram-positive bacteria. Interestingly, lysozyme heated for 20 min, devoid of enzyme activity (HDLz), killed Escherichia coli K12 in a dose-dependent manner, while its bactericidal activity to Staphylococcus aureus was almost similar to that of the nat...