No abstract

the present molecule is too simple to distinguish the out-of-plane oxygen vibration from the rigid body libration of the whole molecule. Concluding remarksIn the present calculations, ordinary spherical scattering factors were used for the carbon and hydrogen atoms, and the effect of bond scattering factor (McWeeny, 1952) and the possibility of the charge transfer as a result of the hydrogen bond (Tsubomura, 1954) were completely neglected. In this respect, the present treatment is still too naive to discuss the distribution of valence electrons. Also, an R value of around 10% is sufficient to determine the atomic positions, but not enough to discuss the effect of bonding. This will be the limit of the ordinary photographic measurement of diffraction intensity.One aim of this paper, however, is to show that even at this level of accuracy the introduction of the aspherical atomic scattering factor can improve the results of structure analyses.In the present study, the changes in bond distances and angles were negligible. However, this result should not be considered to be general. If an atom is not centrosymmetric, the imaginary component in equation (10) will introduce the shift of the positional parameter, as discussed by Dawson (1964a).It can be seen from Table 6, that there still remains a small but systematic discrepancy of the Un component of the oxygen atom. This may be due to the effect of bonding.In order to clarify these points, accurate counter measurements at various temperatures are now being planned.

A conventional Weissenberg camera [Weissenberg (1924). Z. Phys. 23,[229][230][231][232][233][234][235][236][237][238] has been modified for macromolecular crystallography. This camera system consists of a doubly bent LiF monochromator, a newly designed Weissenberg goniometer with multi-layerline screens and its controller. The camera is useful for recording many reflections up to high resolution on a film with high signal-to-background ratio from a crystal with large unit-cell dimensions without losing any of the diffracted beams by screens. The resulting photograph is very easy to index, and the ratio of partially recorded reflections to fully recorded reflections decreases in comparison with an oscillation camera. The multi-layer-line screens are especially practical with a continuous X-ray beam such as synchrotron radiation where both wavelength and band pass can be selected properly. The preparation of a point-focusing monochromator from a single crystal of LiF is described, and the recording of anomalous dispersion profiles is discussed.

The three-dimensional structure of omega-amino acid:pyruvate aminotransferase from Pseudomonas sp. F-126, an isologous alpha 4 tetramer containing pyridoxal 5'-phosphate (PLP) as a cofactor, has been determined at 2.0 A resolution. The diffraction data were collected with a newly developed Weissenberg camera with a Fuji Imaging Plate, using synchrotron radiation. The mean figure-of-merit was 0.57. The subunit is rich in secondary structure and comprises two domains. PLP is located in the large domain. The high homology in the secondary structure between this enzyme and aspartate aminotransferase strongly indicates that these two types of enzymes have evolved from a common ancestor.

A Weissenberg camera for macromolecules with imaging plate data collection system at BL6A and BL18B stations in the Photon Factory is introduced and evaluated. The special feature of these systems is considered matching for both SR-x rays and protein crystallography. This system is user-friendly and can collect a large amount of data to higher resolution from the crystal with large unit cell dimensions. A newly developed camera can be used as a time-resolved Laue camera and a Weissenberg camera. A large image reader (IPR4080) that can scan 400×400 mm2 and 400×800 mm2 sizes of imaging plates has been developed and evaluated. The new data collection system combined with the new camera and IPR4080 will be installed at the BL18B station in October 1994.