MOLECULAR CHARGE EFFECTS ON PROTEIN BEHAVIOR AT HYDROPHOBIC AND HYDROPHILIC SOLID-SURFACES

The adsorption kinetics exhibited by selected charge mutants of bacter iophage T4 lysozyme at silanized silica surfaces were monitored with i n situ ellipsometry. Mutant lysozymes were produced by substitution of lysine with glutamic acid. Each substitution resulted in a decrease i n the net charge of the protein by 2 units. The wild type lysozyme of net charge +9, and two mutants of net charge +7 and +5 were obtained f rom Escherichia coli strain RR1. Adsorption kinetics recorded at hydro philic interfaces were compared to the kinetic behaviour predicted by two simple models for protein adsorption. One allowed for reversible a dsorption followed by conversion to an irreversibly adsorbed from. The second model allowed for irreversible adsorption into one of two stat es directly from solution. Both models suggested that proteins apparen tly absorbed at the interfaces more tightly and occupied a greater int erfacial area with substitution of lysine with glutamic acid. These ef fects were related to the location substitutions relative to other mob ile, solvent-exposed charged residues of the protein, and not to net c harge.