Influence of alkaline phosphatase on phase state of the SM monolayers at the air-water interface

• The different amount of alkaline phosphatase have an influence on the phase transition of SM monolayer at the air–water interface.
• The interfacial mixing ratio of protein/lipid has been calculated by the mass conservation plots.
• The images of AFM and SEM shown the microstructure of the monolayer at 5 and7.8 mN/m.

The Langmuir monolayer is a most suitable model membrane system to study the interfacial interaction between protein and lipid. The surface pressure-area per molecule isotherms of the SM monolayer in the presence of different amount of alkaline phosphatase have been studied in this work. The compression modulus and the interfacial mixing ratio of protein/lipid have been calculated. The different amount of alkaline phosphatase has an influence on the phase transition of SM monolayer at the air–water interface. A coexist state of liquid expanded and liquid condensed is due to the presence of alkaline phosphatase. The process of phase transition from liquid expanded state to coexist state is longer in the presence of more amount of protein. The emergence of coexistence phase state reflects the interaction of the protein and the SM monolayer. The interfacial mixing ratio at the liquid expanded state is higher than that of the coexist state of liquid expanded and liquid condensed. The images of SEM and AFM also shown the microstructure of SM monolayers at two phase states in the presence of alkaline phosphatase.

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