EFFECTS OF ADDITIVES ON IRREVERSIBLE INACTIVATION OF LYSOZYME AT NEUTRAL PH AND 100-DEGREES-C

The mechanism of irreversible inactivation of lysozyme at neutral pH a t 100 degrees C, and effects of additives on the inactivation were inv estigated, The thermoinactivation of lysozyme at neutral pH was caused by intra- and intermolecular disulfide exchange and the production of irreversibly denatured lysozyme, which was destabilized by multiple c hemical reactions other than disulfide exchange, In addition, independ ently, deamidation slightly affected the inactivation by causing a dec rease of electrostatic interaction between positive charges of lysozym e and negative charges of the bacterial cell wall, As for the effects of additives on the inactivation, a small amount of copper ion suppres sed intra- and intermolecular disulfide exchange by catalyzing air oxi dation of heat-induced trace amounts of free thiols, and organic reage nts (acetamide, ethanol, and glycerol) changed the mechanism of the in activation to that under acidic conditions by shifting the pK(a) value s of dissociable residues and also suppressed intermolecular disulfide exchange by decreasing hydrophobic interactions.