COMPUTATION OF THE DIPOLE-MOMENTS OF PROTEINS

A simple and computationally feasible procedure for the calculation of net charges and dipole moments of proteins al arbitrary pH and salt c onditions is described. The method is intended to provide data that ma y be compared to the results of transient electric dichroism experimen ts on protein solutions. The procedure consists of three major steps: (i) calculation of self energies and interaction energies for ionizabl e groups in the protein by using the finite-difference Poisson-Boltzma nn method, (ii) determination of the position of the center of diffusi on (to which the calculated dipole moment refers) and the extinction c oefficient tensor for the protein, and (iii) generation of the equilib rium distribution of protonation states of the protein by a Monte Carl o procedure, from which mean and root-mean-square dipole moments and o ptical anisotropies are calculated. The procedure is applied to 12 pro teins. It is shown that it gives hydrodynamic and electrical parameter s for proteins in good agreement with experimental data.