Growth and mechanical properties of lysozyme crystals

Vickers microhardness of protein crystals of hen egg-white lysozyme was inv estigated by the indentation method. The indentations were clearly made on the crystal surface and no large elastic recovery of them was observed. The value of the hardness was estimated to be 0.2 kgf/mm(2) on the crystals ju st after they were transferred from solution to air. The hardness drastical ly increased with increasing exposure time to air at room temperature. The maximum hardness was 20 kgf/mm(2), which is almost the same as those of van der Waals crystals. The origin of such a change in hardness is explained i n terms of the water contained in protein crystals. (C) 1999 Elsevier Scien ce B.V. All rights reserved.