Prevention of thermal inactivation and aggregation of lysozyme by polyamines

Proteins tend to form inactive aggregates at high temperatures. We show that polyamines, which have a relatively simple structure as oligoamids, effectively prevent thermal inactivation and aggregation of hen egg lysozyme. In the presence of additives, including arginine and guanidine (100 mM), more than 30% of 0.2 mg.mL(-1) lysozyme in sodium phosphate buffer (pH 6.5) formed insoluble aggregates by heat treatment (98degreesC for 30 min). However, in the presence of 50 mM spermine or spermidine, no aggregates were observed after the same heat treatment. The residual activity of lysozyme after this heat treatment was very low (<5%), even in the presence of 100 mM arginine and guanidine, while it was maintained at approximate to50% in the presence of 100 mM spermine and spermidine. These results imply that polyamines are new candidates as molecular additives for preventing the thermal aggregation and inactivation of heat-labile proteins.