COMPARATIVE SURFACE-ADSORPTION BEHAVIOR OF HIGH-DENSITY AND LOW-DENSITY LIPOPROTEINS AS ANALYZED BY FT-IR/ATR SPECTROSCOPY

The adsorption behavior of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) onto a zinc selenide crystal surface and cholesterol-modified ZnSe crystal surface has been studied in terms of adsorption kinetics and isotherms with the use of the FT-IR/ATR technique. Adsorption kinetic plots indicated that the adsorption equilibrium of HDL and LDL is reached at 30-40 min, which is similar to the case for other proteins. From the adsorption isotherms of HDL and LDL, transitions from monolayer adsorption to multilayer adsorption were observed at around 10(-5) M for both lipoproteins. We also observed that the binding of HDL and LDL to a cholesterol-modified ZnSe surface is less than that to an unmodified ZnSe surface. For example, monolayer adsorption density of HDL on the ZnSe surface was 0.23 pmoles/cm(2), whereas it was 0.13 pmoles/cm(2) on the cholesterol-modified ZnSe surface.