A MODEL OF A LOCAL DIELECTRIC-CONSTANT IN PROTEINS

A model for the calculation of the scalar, position-dependent static d ielectric function of an ensemble consisting of polarizable sites and of free relaxing point dipoles at fixed positions is ,proposed. It is based on classical electrostatics and leads to an iteration equation o r nonlinear partial differential equation for the local dielectric con stant. The expressions contain the equations of Debye, Onsager, and Ne umann as special cases and thus might be considered as an extension to inhomogeneous matter. The model may have applications in the case of biological macromolecules in particular proteins where the polar side chains can be identified with the model's dipoles. The algorithm leads to a position dependent dielectric constant in the protein interior i n contrast to the assumption of a homogeneous permittivity throughout the protein. By taking into account the dielectric fine structure insi de the macromolecules we hope that our approach may help to improve co ntinuum electrostatic models of these molecules. The relevant polariza bilities and dipole moments of the amino acids are given and their cor responding local dielectric constants are estimated as a first approxi mation based on the Onsager and Kirkwood equations. (C) 1998 American Institute of Physics.