New morphology, symmetry, orientation and perfection of lysozyme crystals grown in a magnetic field when paramagnetic salts (NiCl_2, CoCl_2 and MnCl_2) are used as crystallizing agents

摘要

Chlorides with different paramagnetic cations such as Ni~(2+), Co~(2+) and Mn~(2+) were used as crystallizing agents instead of NaCl to crystallize hen egg-white lysozyme. NiCl_2 was found to give two types of crystals with different morphologies: one (roof-like) is a new type of orthorhombic P2_12_12_1 crystal with lattice constants a = 79.0A, b = 80.8 A, and c = 37.5 A; the second is an ordinary tetragonal crystal of its characteristic shape with a = b = 80 A and c = 38 A. The appearance of the roof-like shape became dominant in the presence of a magnetic field. In the case of using CoCl_2 and MnCl_2, ordinary tetragonal crystals were formed. A striking fact was that the a-axis of the crystals oriented along the magnetic field when CoCl_2 was used, as opposed to the usual c-axis orientation. Large and optically perfect lysozyme crystals can be obtained in a magnetic field when NiCU or MnCl_2 is used as a crystallizing agent. These profound effects of the paramagnetic cations may be caused by the coordination of Ni~(2+) and Co~(2+) ions to a lysozyme molecule, which was found by X-ray crystallography.