| Abstract: | The ultrasonic absorption spectra of proteins in solution generally show relaxational behaviour. There will be a corresponding dispersion of sound velocities accompanying each relaxation. The compressibility of the protein as measured by sound velocity techniques will therefore include a relaxational contribution. We have evaluated this contribution for a number of proteins and found that in some cases the relaxational contribution is a significant fraction of the total compressibility. The relaxational contribution will be large only if the molecule has a large number of degrees of freedom with low force constants. However, such motions are likely to be those involved in the biological functioning of the molecule. Care is needed in interpreting the relaxation spectrum since proton transfer processes give large apparent relaxational compressibilities. |
