Study on the insertion process of human apolipoprotein H into spread phospholipid monolayers by monitoring the initial change in surface pressure

A monolayer study on the interaction of human apolipoprotein H (ApoH) and phospholipids is reported in the present work. The initial rate of surface pressure change (dπ/dt)ini is used to characterize the insertion process of ApoH into the phospholipid monolayers spread at the air/water interface. The results show that the value of (dπ/dt)ini of ApoH will rise when the content of DMPS in the DMPS/DMPC monolayer mixture increases, indicating an increase in membrane insertion ability of the protein. The protein adsorption can be screened by sodium ions but not by calcium ions. When the pH is lower than 6, the initial rate of surface pressure change of the protein will increase sharply indicating that acidic environment is an important factor influencing the membrane insertion process of ApoH.