Roles of γ-globulin in the dynamic interfacial behavior of mixed dipalmitoyl phosphatidylcholine/γ-globulin monolayers at air/liquid interfaces

This study investigated the roles of γ-globulin in the dynamic interfacial behavior of dipalmitoyl phosphatidylcholine (DPPC)/γ-globulin monolayers at air/liquid interfaces at 25°C. The surface tension behavior demonstrated that γ-globulin had a large adsorption time scale. Moreover, the surface pressure-area hysteresis behavior of adsorbed γ-globulin monolayers suggested that no significant desorption occurred during the compression stage, and the respreading of γ-globulin molecules at the interface during the expansion stage was slow. From the hysteresis behavior of adsorbed γ-globulin monolayers with spread DPPC molecules, it was found that γ-globulin molecules were expelled from the interface as DPPC molecules were in a condensed state. The squeeze-out of γ-globulin molecules seemed to induce the loss of DPPC molecules at the interface with the extent depending on the initial γ-globulin surface concentration. Furthermore, the expelled γ-globulin molecules reentered the monolayer and participated in the surface pressure increase during the following expansion stage. The exclusion of γ- globulin associated with the removal of DPPC during monolayer compression and the re-entry of γ-globulin during subsequent monolayer expansion represented a mechanism for DPPC depletion and γ-globulin enrichment at the interface, which may explain the inhibitory effect of certain proteins on the surface activity of DPPC. (C) 2000 Academic Press.