Transverse sound velocity of cross-linked tetragonal hen egg-white (HEW) lysozyme crystals containing large amount of water in the crystal was measured using ultrasonic pulse-echo method. All elastic constants of cross-linked crystals were observed to be $C_{11}=C_{22}=5.50\text{GPa}$, $C_{12}=4.33\text{GPa}$, $C_{13}=C_{23}=3.94\text{GPa}$, $C_{33}=5.22\text{GPa}$, $C_{44}=C_{55}=0.68\text{GPa}$, and $C_{66}=0.84\text{GPa}$, respectively. We found that the elastic constants of the cross-linked crystals are identical to those of the intrinsic ones without cross-linking. Moreover, we found that tetragonal HEW lysozyme crystals that enclose large amount of water show decreased elastic constants (softening). In particular, the shear elastic constants $C_{44}=C_{55}$ and $C_{66}$ showed more softening effect comparing with other elastic components.

• Received 6 October 2008

DOI:https://doi.org/10.1103/PhysRevE.79.061917