Ultrasonic absorption in aqueous solution of lysozyme

The titration curve of ultrasonic absorption at 2.82 MHz in aqueous solutions of lysozyme measured by Zana and Lang [ J. Phys. Chem. , 74 , 2734 (1970)] is theoretically analyzed. The maxima at pH 3 and pH 11 are describable with proton‐transfer reactions of dissociable carboxyl and amino groups by assuming that volume changes due to the reactions are 2.3 and 5.2 cm 3 /mole, respectively, which are appreciably smaller than those of simple amino acids. The remaining, pH‐independent excess absorption over solvent is measured at frequencies ranging from 3 to 150 MHz. The absorption is ascribed to the internal loss of protein. The complex compressibility β′ p − i β″ p of lysozyme molecule is evaluated as β′ p = 7.2 × 10 −12 cm 2 /dyne and β″ P = 4.3 × 10 −14 cm 2 /dyne from the increments over solvent in absorption as well as in sound velocity.