Success in measuring transverse sound velocity allowed us to determine, for the first time, all six elastic constants of a protein crystal. An ultrasonic pulse-echo method was used to perform sound velocity measurements on tetragonal hen egg-white (HEW) lysozyme crystals that were partially dehydrated at 42% relative humidity. The measurements were performed using the (110), (101), and (001) crystallographic faces. Thus, all six elastic constants of the dehydrated tetragonal HEW lysozyme crystals were determined: $C_{11}=C_{22}=12.44\mathrm{GPa}$, $C_{12}=7.03\mathrm{GPa}$, $C_{13}=C_{23}=8.36\mathrm{GPa}$, $C_{33}=12.79\mathrm{GPa}$, $C_{44}=C_{55}=2.97\mathrm{GPa}$, and $C_{66}=2.63\mathrm{GPa}$. In addition, for the hydrated crystals, the longitudinal sound velocities along the [110] direction and the direction normal to the (101) face were measured. From these results, all the components of elastic constants in the hydrated crystals were extrapolated.

• Received 11 August 2004

DOI:https://doi.org/10.1103/PhysRevE.73.041910