Adiabatic compressibility of globular proteins.

The adiabatic compressibility of several globular proteins has been measured by using an ultrasonic technique in the frequency range 0.5 to 10 MHz. The contributions to the measured compressibility from the protein matrix and from surface processes involving ionization of side chains and solvation effects are discussed. The internal protein compressibility is very low, indicating the existence of "dynamic domains" which are tentatively assigned to secondary structure elements.