Structural Change in Dimyristoyl Phosphatidyl Choline (DMPC) Molecule Alkyl Chains on the Addition of Cholesterol to DMPC Monolayer: Specific Addition Effect of Cholesterol

Abstract

We have investigated the morphology of dimyristoyl phosphatidyl choline (DMPC)-cholesterol mixed monolayer formed on the water surface by dropping method using surface tension measurement (STm), Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IERS). STm results showed negative deviation of the limiting molecular area (A 0 ) of cholesterol occurred when cholesterol was added to the DMPC monolayer. BAM images showed the expandable DMPC monolayer changed to the condensed rigid monolayer at more than cholesterol mole fraction (x Chol ) 0.4. IERS recordings showed that the addition of cholesterol at x Chol = 0.4 occurred structural change from gaucheto transconformation of two DMPC molecule alkyl chains. From these results, it is found that cholesterol molecule has specific properties that cause structural transition of DMPC molecule alkyl chains.

Morphology Observation of Two-Dimensional Monolayers of Model Proteins on Water Surface as Revealed by Dropping Method

“…It was also reported that DPPC and DMPC mixed monolayers had the properties of pure DPPC at low mole fractions of x DMPC and neat DMPC at high x DMPC , which showed their three-dimensional bulk structural properties [17]. In the above reports [13][14][15][16][17], we discussed the applications of the monolayers prepared by the DM method as a model biological membrane. Biological membrane constituents, such as phospholipids and membrane proteins, express and perform their functions using the surrounding water as a medium.…”

“…Each solution was spread on a purified water surface using a 50 µL syringe (Hamilton Corp., Hamilton, NY, USA) to prepare the monolayer. The details of monolayer preparation using the DM have been reported in our previous articles [13][14][15][16][17]. In brief, a drop of 1 µL volume solution was gently put on the surface of the water.…”

“…Brewster angle microscopy (BAM) for visualizing and capturing the morphology of the GD and Al monolayers was carried out using a BAM microscope (EMM633K; Filgen Inc., Nagoya, Japan) equipped with USB-CAP-type (GV-USB2; I-O DATA DEVICE, Inc., Ishikawa, Japan) image analysis software [13][14][15][16][17][18]. BAM showed the monolayer image that was formed due to the difference in refractive indices between the monolayer and the pure water phase.…”

“…Such a fluidic DPPC monolayer also showed a specific condensation behavior through the action of cholesterol [13,15]. The addition of cholesterol in the dimyristoyl PC (DMPC) monolayer caused the transition from a liquid expanded (LE) state to a liquid condensed (LC) state with the structural transition (gauche-to-trans conformation) of alkyl chains in DMPC [16] molecules. It was also reported that DPPC and DMPC mixed monolayers had the properties of pure DPPC at low mole fractions of x DMPC and neat DMPC at high x DMPC , which showed their three-dimensional bulk structural properties [17].…”