Kinetic measurement of the interaction between a lysozyme and its immobilized substrate analogue by means of surface plasmon resonance

A method for evaluating the association and dissociation rate constants of interaction between a lysozyme and its substrate analogue, an immobilized p-aminophenyl-tri-N-acetyl-β-chitotrioside, by means of surface plasmon resonance has been developed. Site-specific immobilization of p-aminophenyl-tri-N-acetyl-β-chitotrioside, which is a product of p-nitrophenyl-tri-N-acetyl-β-chitotrioside, on carboxymethyldextran linked to the surface of the cuvette of the instrument, IAsys, was carried out by catalysis with EDC/NHS. The kinetic parameters of the interaction between hen or human lysozyme and the immobilized substrate analogue indicated that a larger dissociation constant of the human lysozyme-immobilized substrate analogue complex depended on a smaller association rate constant. The kinetic parameters of the interaction between the immobilized substrate analogue and a mutant hen lysozyme, in which Arg14 and His15 are deleted, with higher activity than the wild type hen lysozyme were measured. It was suggested that the higher activity of the mutant lysozyme was due to faster removal of the substrate from the active site cleft and/or the formation of a stabler and better complex as to hydrolysis.