Interfacial tension in adsorption of lysozyme onto a lipid monolayer formed at a water/chloroform interface

•Dynamics of lysozyme adsorption onto a lipid monolayer membrane.•Interfacial tension by a non-invasive quasi-elastic laser scattering method.•Effect of an electrolyte on lysozyme adsorption behavior.

Using a quasi-elastic laser scattering (QELS) method, we determined the changes in the interfacial tension of a lipid monolayer membrane, composed of either 1,2-dioleoyl-sn-glycero-3-phospho-l-serine sodium salt (DOPS) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), at the water/chloroform interface upon the addition of lysozyme. The measurements were performed in the presence of electrolytes of different concentrations and using lipids that vary the net charge of the monolayer membrane. As a result, the interfacial tension was observed to decrease in three stages. In the case of DOPS, there was a lag time wherein the interfacial tension did not change, which lasted from several tens of seconds to several hundreds, following electrostatic interaction between lysozyme and the lipid monolayer membrane. On the other hand, the DOPC monolayer membrane decreased its interfacial tension without such a lag time after lysozyme addition. The lag time was attributed to the strong electrostatic interaction between the lysozyme and the DOPS monolayer membrane, which delayed the hydrophobic interaction that causes a change in the overall structure and conformation of lysozyme and lipids.

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