SURFACE-TENSION KINETICS OF THE WILD-TYPE AND 4 SYNTHETIC STABILITY MUTANTS OF T4 PHAGE LYSOZYME AT THE AIR-WATER-INTERFACE

Surface tension kinetics exhibited by the wild type and selected stabi lity mutants of T4 lysozyme at the air-water interface were monitored with DuNouy tensiometry. Mutant lysozymes were produced by substitutio n of the isoleucine at position 3 with cysteine, leucine, glycine, and tryptophan. Each substitution resulted in an altered structural stabi lity quantified by a change in the free energy of unfolding. Surface p ressure kinetics were compared to the kinetic model evolving from a si mple model for protein adsorption. This model allowed for parallel, ir reversible adsorption into two states directly from solution, where st ate 2 molecules were more tightly bound to the surface and occupied gr eater interfacial area than state 1 molecules. Moreover, the model all owed state 2 molecules to increase spreading pressure more than state 1 molecules. occupying the same interfacial area. The model indicated that less stable variants of T4 lysozyme have a greater tendency to ad sorb in state 2, and state 2 molecules increase spreading pressure mor e than state 1 molecules occupying the same interfacial area. While ag reement between the model and experimental data was very good at low c oncentration, these results suggest that a more comprehensive two-stat e model should account for the influence of surface coverage on the ad sorption rate constants. (C) 1997 Academic Press