Kinetic Studies on the Chemical Modification of Lysozyme by N-bromosuccinimide and Its Protection by Substrates and Analogs

The chemical modification of tryptophan residues of hen egg-white lysozyme by N-bromosuccinimide (NBS) was studied kinetically by the stopped-flow method, monitoring changes in absorbance and fluorescence. One most rapidly reacting tryptophan residue, probably Trp 62, was clearly distinguished from four other residues in terms of rate of modification. This residue was protected by ethylene glycol chitin, N-acetyl glucosamine (NAG), and tri-NAG, but not by gluconolactone. The dissociation constant Kd of the enzyme-ligand complex was obtained from the protection effects. These results are in good agreement with results previously obtained.