COMPARISON OF THE STRUCTURES OF DIMYRISTOYLPHOSPHATIDYLCHOLINE IN THEPRESENCE AND ABSENCE OF CHOLESTEROL BY MOLECULAR-DYNAMICS SIMULATIONS

Molecular dynamics simulations were carried out on bilayers consisting of dimyristoylphosphatidylcholine dihydrate (DMPC) and DMPC-cholester ol at a 1:1 mole ratio. The calculations were carried out under NPT co nditions (constant number of molecules, pressure and temperature, with volume and bilayer area per molecule free to change). Raising the sim ulation temperature from 200 to 325 K caused the surface area per DMPC molecule to increase from 39 to 50 Angstrom(2) in the pure bilayer: t he area per heterodimer of DMPC and cholesterol increased from 79 to 9 1 Angstrom(2) for the same temperature range. The properties of the hi gh-temperature state approximates that of a liquid crystalline array, although the area per molecule in the pure DMPC bilayer remains smalle r than the experimentally determined value of 65-69 Angstrom(2) The nu mber of gauche bonds, the P-N vector angle distribution, and the inter nal dipole potential are also reported for the simulated liquid crysta lline state in the presence and absence of cholesterol.