Many kinds of complicated crystal structures have appeared in the transition metal sulfide system. Simulation by the matrix method could explain the diffuse scattering observed in nonstoichiometric titanium sulfides with stacking faults, in Ti1.42S2 with short-range order of Ti vacancies, and in some channel-type composite crystals such as Ba0.7Cr2S3.7 with two-directional disorder of positions of filling columns. Crystal structures of incommensurate layered composite crystal (PbS) 1.12VS2, columnar composite crystals Ba10/9Fe2S4 and Ba9/8Fe2S4, and incommensurate columnar composite crystals SrxTiS3 (x=1.1-1.2) were successfully analyzed based on the superspace group approach.
The structure and function of homodimeric L-2-haloacid dehalogenase from Pseudomonas sp. YL has been investigated by X-ray crystallographic methods. Each subunit of the enzyme consists of two domains. The core domain has a unique α/β structure which is different from the α/βhydrolase fold, and contains almost all the active site residues. The subdomain for dimerization has a four-helix bundle structure. The structure analysis of the complex between the S175A mutant and L-2-chlorobutyrate has revealed the structure of the corresponding ester intermediate. This suggests that the catalysis of the enzyme must proceed in SN2 substitution reaction via the ester intermediate.
Structural change of minerals in weathering and alteration processes at the surface of the crust is one of the important topics in earth science. In order to reveal its basic mechanisms, transmission electron microscopy (TEM) with atomic resolution is effective. Some examples related to alterations of micas are demonstrated in this paper. One of the obstacles to investigate these hydrous minerals, electron radiation damage, is being solved by new image recording systems, imaging plates and sensitive CCD cameras.
The structure of hydroxylamine oxidoreductase from Nitrosomonas europaea has been determined by multiple isomorphous replacement. The crystals, space group P63, were shown to be hemihedrally twinned. The observed intensities were found to be detwinned by the least squares method after the Britton's algorithm [Britton, D. (1972) . Acta Cryst. A28, 296-297], when several sets of intensity data were useful. The programs coded by Fortran language succeeded in determining the scale factors and degrees of twinnings. The analysis of data collected at various positions of one crystal of this enzyme suggested the heterogeneous distribution of twinning in the crystal.