New morphology, symmetry, orientation and perfection of lysozyme crystals grown in a magnetic field when paramagnetic salts (NiCl2, CoCl2 and MnCl2) are used as crystallizing agents

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 1 2 1 2 1 crystal with lattice constants a =79.0 A, 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 NiCl 2 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.