OBSERVATION OF LATTICE-DEFECTS IN ORTHORHOMBIC HEN-EGG WHITE LYSOZYME CRYSTALS WITH LASER SCATTERING TOMOGRAPHY

Laser scattering tomography (LST) has been applied to observe lattice defects in protein crystals for the first time. Hen-egg white lysozyme crystal of orthorhombic modification was grown by a batch method using heterogeneous crystallization method (50 mM Tris-HCl buffer, pH 8.0, NaCl 4%, lysozyme concentration 2%, 35-degrees-C). The crystal sizes employed were 1-2 mm in thickness, and 5-7 mm in length. The following conclusions were obtained: (1) LST figures were observed from the crystal portions where no defect was detectable by the naked eye or optical microscopy. (2) The polarization dependence proved that both bulk-type and point-type defects are present. The bulk-type LST patterns were often parallel to the crystal edges, and are assumed to correspond to inclusions. The point-type defects were assumed to be micro-defects, such as vacancies, precipitates or impurities. (3) Densities of the micro-defects changed when the laser beam position was changed inside the crystal. A common tendency was seen in that the density from the portion closer to the crystal surface was larger than that from the interior portion. (4) Growth boundaries were detectable in the LST image, being parallel to low-indexed growth surfaces. From these results, we conclude that LST is effective to macroscopically characterize the protein crystals in a non-destructive manner.