The adsorption of phosvitin at the air-water interface has been teins to adsorb at phase boundaries, especially at air/water studied to elucidate the influence of electrostatic forces on protein and oil/water interfaces, arises because of their amphiphilic adsorption at liquid interfaces. Because of its polyanionic characnature, the exact role of electrostatic forces in the adsorption ter, adsorption of phosvitin at the air-water interface takes place process is not well understood. Several studies relating to only at low pH, but not near neutral pH. Phosvitin adsorbed at adsorbed and spread proteins films at various interfaces have an initial pH of 2.0 is completely desorbed from the interface been reported (3-14). However, only a few of those studies when the pH is increased to neutral pH. The saturated monolayer have dealt with the role of electrostatic forces in the kinetics coverage for phosvitin is about 1.25 mg/m 2 at pH 2.0. However, in of protein adsorption at the air-water interface (6, 8). Macspite this significant amount of adsorption, no decrease in surface tension occurs. Instead, a consistent increase in surface tension of Ritchie and Alexander (6) reported on the effects of spread the solution occurs, which apparently violates the Gibbs adsorpmonolayers of various negatively and positively charged tion equation. A model based on the configuration of phosvitin at molecules on adsorption of lysozyme from a dilute solution the interface has been proposed to explain the thermodynamic to the air-water interface. Although this approach is useful reasons for this apparent violation of the Gibbs equation. It is for elucidating the effects of charge-charge interactions on shown that phosvitin is anchored to the interface only via a short protein adsorption to a charged monolayer, information re-C-terminus hydrophobic segment and the rest of the highly hydrogarding interaction of the force field of a clean interface philic molecule is suspended in the subsurface. These suspended with the electrostatic free energy of a protein on the latter's loops exert an electrostatic pull on surface water molecules, causrate of adsorption at the interface cannot be obtained from ing an increase in surface tension. However, the reduction in free such an approach.
energy resulting from removal of the hydrophobic segment from
The influence of electrostatic free energy of a protein on water to the interface is much greater than the increase in surface tension caused by charge-dipole interactions, so that there is actu-its adsorption at liquid interfaces can be best understood by ally a net reduction in free energy of the system. Thus, although studying the kinetics of adsorption of phosvitin. Phosvitin adsorption of phosvitin apparently violates the Gibbs adsorption is a phosphoglycoprotein found in egg yolk of all avian equation, it does not violate the basic thermodynamic principle. species. At pH 7.0 it has a net charge of about 0179. The The results also show that proteins can adsorb to an interface high net charge and the sensitivity of its conformation to against seemingly excessive electrostatic repulsive forces through changes in its electrostatic free energy make phosvitin an attachment of only a small hydrophobic peptide segment. α§ 1996 ideal candidate for studying the influence of electrochemical Academic Press, Inc. potential on adsorption of proteins at interfaces.