Purification and characterization of lysozyme from hemolymph of Heliothis virescens larvae

Lysozyme is an important antibacterial protein in the insect defense system. Lysozyme was isolated from hemolymph of Heliothis virescens larvae using gel filtration and ion-exchange chromatography. Heliothis lysozyme had a molecular mass of 16,000 daltons by SDS-PAGE. Using acid gel electrophoresis, Heliothis lysozyme migrated faster than egg white lysozyme. The pI of Heliothis lysozyme was estimated as greater than 9.5. Heliothis lysozyme had specific bactericidal activity against three Gram-positive bacteria but no activity against Escherichia coli. The bactericidal activity was stable at 100 degrees C at pH 3.0 after 60 min incubation, but was labile at 100 degrees C at pH 6.8 after 60 min incubation. Heliothis lysozyme was an inducible protein that increased 9 times when comparing unvaccinated with vaccinated larvae. Lysozyme from H. virescens was more similar in molecular mass, heat sensitivity and pH sensitivity to lysozyme isolated from Galleria mellonella and Bombyx mori than to lysozyme isolated from Hyalophora cecropia.