Adsorption of lysozyme and some acetyl derivatives at the air‐water interface

Abstract

Abstract An examination was made of adsorbed and spread films of lysozyme and a series of its acetyl derivatives at the air‐water interface. Direct observations of adsorption and desorption were carried out by measuring the surface pressure and surface radioactivity of films of native and heat‐denatured 1‐ 14 C‐acetyl lysozyme. Acetylation of as little as one residue per molecule significantly alters the surface properties of lysozyme. Films of lysozyme derivatives spread on low ionic strength buffer give pressure‐area isotherms which are less expanded than those obtained on concentrated salt solutions because in the former case protein is lost to the subphase. The isotherms of native and heat‐denatured protein‐films spread on 3.5 M KC1 are independent of the degree of modification and compression rate and no desorption occurs. Pressure‐area isotherms of adsorbed films show that a low subphase concentration gives rise to a film containing extensively unfolded molecules, while higher concentrations lead to the formation of a film of higher surface concentration containing incompletely unfolded molecules. Spread protein films generally contain more completely unfolded molecules than adsorbed films and more expanded interfacial films are obtained when heat‐denatured molecules adsorb than when native molecules adsorb from solutions of the same concentration.