Chemical characterization of the dapsone binding site of lysozyme.

The binding of dapsone to hen egg white lysozyme has been studied using fluorescence spectroscopy. At low concentrations the drug binds lysozyme with a Ka = 3.3 X 10(4) M-1 forming a 1:1 complex. At high concentrations the protein was found to bind the drug in a cooperative manner at two sites with an average association constant of 6.3 X 10(4) M-1. Both Trp-108 and Trp-62 of lysozyme are involved in the association process. Acetylation of the lysine residues increased the affinity of the drug to the protein. However, drug association showed no effect on the enzymatic activity of the protein.