DETERMINATION OF COMPONENT VOLUMES OF LIPID BILAYERS FROM SIMULATIONS

An efficient method for extracting volumetric data from simulations is developed. The method is illustrated using a recent atomic-level mole cular dynamics simulation of L-alpha phase 1,2-dipalmitoyl-sn-glycero- 3-phosphocholine bilayer. Results from this simulation are obtained fo r the volumes of water (V-W), lipid (V-L), chain methylenes (V-2), cha in terminal methyls (V-3), and lipid headgroups (V-H), including separ ate volumes for carboxyl (V-COO), glyceryl (V-gl), phosphoryl (V-PO4), and choline (V-chol) groups. The method assumes only that each group has the same average volume regardless of its location in the bilayer, and this assumption is then tested with the current simulation. The v olumes obtained agree well with the values V-W and V-L that have been obtained directly from experiment, as well as with the volumes V-H, V- 2, and V-3 that require certain assumptions in addition to the experim ental data. This method should help to support and refine some assumpt ions that are neccessary when interpreting experimental data.