Relationships between conformational changes and antimicrobial activity of lysozyme upon reduction of its disulfide bonds

The structural changes and antimicrobial activity of hen lysozyme in which its disulfide bonds were reduced to varying degrees, were investigated. Lysozyme was reduced with 2 mM dithiothreitol at pH 8 and 30 degreesC from 0.5 to 4 h, and the released sulfhydryl groups were modified by iodoacetamide. The resulting reduced lysozymes were then tested for their antimicrobial activity against Salmonella enteritidis, Escherichia coli, Proteus mirabilis and Serratia marcescens. The treatment was found to induce lysozyme to expose its surface hydrophobicity and intrinsic fluorescence, change its CD behaviour and increase its binding affinity to the bacterial membranes, thereby enhancing its antimicrobial activity against Gram-negative bacteria, the extent of which depended on the degree of reduction and bacterial strains used. The reduced lysozymes showed greater bactericidal activity toward S. enteritidis than other strains tested and the partially reduced form was more powerful than the fully reduced one. (C) 2003 Elsevier Ltd. All rights reserved.