The crystal structures of the copper enzyme phenylethylamine oxidase from the Gram-positive bacterium Arthrobacter globiformis (AGAO) have been determined and refined for three forms of the enzyme: the holoenzyme in its active form (at 2.2 A resolution), the holoenzyme in an inactive form (at 2.8 A resolution), and the apoenzyme (at 2.2 A resolution). The holoenzyme has a topaquinone (TPQ) cofactor formed from the apoenzyme by the post-translational modification of a tyrosine residue in the presence of Cu2+. Significant differences between the three forms of AGAO are limited to the active site. The polypeptide fold is closely similar to those of the amine oxidases from Escherichia coli [Parsons, M. R., et al. (1995) Structure 3, 1171-1184] and pea seedlings [Kumar, V., et al. (1996) Structure 4, 943-955]. In the active form of holo-AGAO, the active-site Cu atom is coordinated by three His residues and two water molecules in an approximately square-pyramidal arrangement. In the inactive form, the Cu atom is coordinated by the same three His residues and by the phenolic oxygen of the TPQ, the geometry being quasi-trigonal-pyramidal. There is evidence of disorder in the crystals of both forms of holo-AGAO. As a result, only the position of the aromatic group of the TPQ cofactor, but not its orientation about the Cbeta-Cgamma bond, is determined unequivocally. In apo-AGAO, electron density consistent with an unmodified Tyr occurs at a position close to that of the TPQ in the inactive holo-AGAO. This observation has implications for the biogenesis of TPQ. Two features which have not been described previously in amine oxidase structures are a channel from the molecular surface to the active site and a solvent-filled cavity at the major interface between the two subunits of the dimer.

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The bacterial flagellum is a motile organelle, and the flagellar hook is a short, highly curved tubular structure that connects the flagellar motor to the long filament acting as a helical propeller. The hook is made of about 120 copies of a single protein, FlgE, and its function as a nano-sized universal joint is essential for dynamic and efficient bacterial motility and taxis. It transmits the motor torque to the helical propeller over a wide range of its orientation for swimming and tumbling. Here we report a partial atomic model of the hook obtained by X-ray crystallography of FlgE31, a major proteolytic fragment of FlgE lacking unfolded terminal regions, and by electron cryomicroscopy and three-dimensional helical image reconstruction of the hook. The model reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.

Electrical data obtained from deep level transient spectroscopy investigations on deep defect centers in the 3C, 4H, and 6H SiC polytypes are reviewed. Emphasis is put on intrinsic defect centers observed in as‐grown material and subsequent to ion implantation or electron irradiation as well as on defect centers caused by doping with or implantation of transition metals (vanadium, titanium, chromium, and scandium).

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4H-SiC(0001), (000 " 1 1), and (11 " 2 20) have been directly oxidized by N 2 O at 1300 C, and metal-oxide-semiconductor (MOS) interfaces have been characterized. The interface state density has been significantly reduced by N 2 O oxidation on any face, compared to conventional wet O 2 oxidation at 1150 C. Planar n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on 4H-SiC(0001), (000 " 1 1) and (11 " 2 20) faces have shown effective channel mobilities of 26, 43, and 78 cm 2 /Vs, respectively. Secondary ion mass spectrometry analyses have revealed a clear pileup of nitrogen atoms near the MOS interface. The thickness of the interfacial transition layer can be decreased by N 2 O oxidation. The crystal face dependence of the interface structure is discussed. A simple consideration of chemistry indicates that NO, generated from the decomposition of N 2 O, may be a more efficient oxidant of carbon than O 2 .

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Step bunching in chemical vapor deposition of 6H– and 4H–SiC on off-oriented {0001} faces is investigated with cross-sectional transmission electron microscopy. On an off-oriented (0001)Si face, three Si–C bilayer-height steps are the most dominant on 6H–SiC and four bilayer-height steps on 4H–SiC. In contrast, single bilayer-height steps show the highest probability on a (0001̄)C face for both 6H– and 4H–SiC epilayers grown with a C/Si ratio of 2.0. The increase of C/Si ratio up to 5.0 induces the formation of multiple-height steps even on a C face. The bunched step height corresponds to the unit cell or the half unit cell of SiC. The mechanism of step bunching is discussed with consideration of surface formation processes.