Electrical fluctuations on the surfaces of proteins from hydrodynamic data.

We calculate the electrical capacitance on the surfaces of protein molecules from hydrodynamic data of the proteins. Then we estimate the electrical fluctuations (charge, voltage) through the fluctuation-dissipation theorem, which links the electrical capacitance of the system with these fluctuations. From the intrinsic viscosity of the proteins, we estimate the polarizability, which leads to knowledge of the field and dipole fluctuations. From the fitting of the capacitance, polarizability, and electrical fluctuations as a function of the molecular weight of the proteins, we report numerical equations that make it possible to estimate these physical magnitudes for a given protein, knowing the molecular weight. Charge fluctuations are in fractions of unit charge range, voltage fluctuations are in the three-mV-digit range, field fluctuations are in the two-digit mV/nm (10(6) V/m) range, and the dipole moment fluctuations range from two to three digits, times the dipole moment of the water molecule. These surface properties of proteins have not been reported before.