Distributed feedback surface-emitting laser with air/semiconductor gratings embedded by mass-transport assisted wafer fusion technique

We report on a distributed feedback InGaAsP MQW laser with air/semiconductor gratings embedded by wafer-fusion technique with the assistance of mass-transport phenomenon for the first time. The air/semiconductor gratings with 0.4-/spl mu/m period and 0.2-/spl mu/m depth are successfully fabricated inside the device, and a single longitudinal mode oscillation at about 1.28 /spl mu/m is demonstrated under pulsed condition at room temperature. The threshold current density is estimated to be about 1.4 kA/cm/sup 2/. It is also shown that the device has a surface-emitting function since it has a low loss multiquantum-well waveguide with grating output coupler.     

High-Precision Alignment and Bonding System for the Fabrication of 3-D Nanostructures

We successfully developed a high-precision wafer alignment and bonding system for the fabrication of a variety of 3-D nanostructures. To control the wafer positions with high accuracy during the wafer-bonding process, we improved upon a design of the conventional mask-alignment stage. A stress sensor was incorporated to measure the load between the two wafers. In addition, the parallelism of the wafers was monitored by an optical interferometry system. To determine alignment errors in both the and directions simultaneously, we devised an alignment method consisting of crossed vernier scales. We demonstrated that the new alignment and bonding system allowed us to realize precise 3-D photonic crystals with the alignment inaccuracy of < 100 nm at most, and we show that the best experimental error achieved to date was < 25 nm. As this system has the benefit of more readily and intuitively determining the absolute positions of the two wafers, it can be applied to the fabrication of a wide variety of nanoscale multilayer devices.     

Structure of 3-isopropylmalate dehydrogenase in complex with 3-isopropylmalate at 2.0 A resolution: the role of Glu88 in the unique substrate-recognition mechanism

BACKGROUND: 3-Isopropylmalate dehydrogenase (IPMDH) and isocitrate dehydrogenase (ICDH) belong to a unique family of bifunctional decarboxylating dehydrogenases. Although the ICDH dimer catalyzes its reaction under a closed conformation, known structures of the IPMDH dimer (without substrate) adopt a fully open or a partially closed form. Considering the similarity in the catalytic mechanism, the IPMDH dimer must be in a fully closed conformation during the reaction. A large conformational change should therefore occur upon substrate binding. RESULTS: We have determined the crystal structure of IPMDH from Thiobacillus ferrooxidans (Tf) complexed with 3-isopropylmalate (IPM) at 2.0 A resolution by the molecular replacement method. The structure shows a fully closed conformation and the substrate-binding site is quite similar to that of ICDH except for a region around the gamma-isopropyl group. The gamma group is recognized by a unique hydrophobic pocket, which includes Glu88, Leu91 and Leu92 from subunit 1 and Val193' from subunit 2. CONCLUSIONS: A large movement of domain 1 is induced by substrate binding, which results in the formation of the hydrophobic pocket for the gamma-isopropyl moiety of IPM. A glutamic acid in domain 1, Glu88, participates in the formation of the hydrophobic pocket. The C beta and C gamma atoms of Glu88 interact with the gamma-isopropyl moiety of IPM and are central to the recognition of substrate. The acidic tip of Glu88 is likely to interact with the nicotinamide mononucleotide (NMN) ribose of NAD+ in the ternary complex. This structure clearly explains the substrate specificity of IPMDH.     

Semiconductor three-dimensional and two-dimensional photoniccrystals and devices

Semiconductor three-dimensional (3-D) and two-dimensional (2-D) photonic crystals and their effects on the control of photons are investigated for possible applications to optical chip and functional devices. First we review our approaches creating full 3-D photonic bandgap crystals at near-infrared wavelengths, and also functional devices based on 2-D photonic crystals where the focus is on surface-emitting-type channel-drop filtering devices utilizing single defects in 2-D photonic crystal slabs. Then, we describe the recent progress on 3- and 2-D crystals. On 3-D crystals, the effect of the introduction of a light emitter into the 3-D photonic crystal is investigated, and the design of a single defect cavity is performed. On the 2-D photonic crystals, the photonic states are investigated from the perspective of their polarization properties     

Purification and characterization of beta-N-acetylglucosaminidase from Alteromonas sp. strain O-7

beta-N-Acetylglucosaminidase (EC 3.2.1.30) was purified from the outer membrane of a marine bacterium, Alteromonas sp. strain O-7. The enzyme (GlcNAcase A) was purified by successive column chromatographies. The purified enzyme was found to be homogeneous on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The molecular mass and pI of GlcNAcase A were 92kDa and 4.9, respectively. The optimum pH and temperature were 6.0-7.0 and 45 degrees C, respectively. GlcNAcase A was stable up to 40 degrees C at pH 7.0, and hydrolyzed N-acetylchitooligosaccharides from dimer to hexamer. The amino-terminal 16 amino acid residues of GlcNAcase A were sequenced.     

Analysis of single-mode optical Y-junction by the boundedstep and bend approximation

An approximate method for analyzing planar optical Y-junctions is presented. The junction structure is replaced by a discrete succession of bounded waveguide segments, and the presence of waveguide bends is assumed. Using this approximation, single-mode symmetrical Y-junctions operated as power dividers are investigated numerically. It is shown that strong mode conversion occurs between the guided and radiation modes of the local normal mode. A perturbation analysis shows that reflected fields are negligible. Reliable values of the transmitted power are obtained     

Study of modification pattern-RNAi activity relationships by using siRNAs modified with 4'-thioribonucleosides

A detailed study of the modification pattern-RNAi activity relationships by using siRNAs that are modified with 4'-thioribonucleosides has been carried out against photinus luciferase and renilla luciferase genes in cultured mammalian NIH/3T3, HeLa, and MIA PaCa-2 cell lines. When the photinus luciferase gene was targeted, all of the modified siRNAs showed activity equal to, or less than the unmodifed siRNA. In contrast, all modified siRNAs that have a similar modification pattern showed activity equal to or much higher than the unmodified siRNA when tested with the renilla luciferase gene. These results indicated that siRNAs such as RNA33 and RNA53, which each have four residues of the 4'-thioribonucleoside unit on both ends of the sense strand and four residues on the 3'-end of the antisense strand, were the most effective. Accordingly, we succeeded in developing modified siRNAs that have the greatest number of 4'-thioribonucleosides without loss of RNAi activity, and that exhibit potent RNAi activity against two target genes in three different cell lines. Our findings also indicate the significance of target sequences and cell lines when RNAi activity is compared with that of the unmodified siRNA.     

Functional reconstitution of an active recombinant human chymase from Pichia pastoris cell lysate

We have previously reported efficient production of mature human chymase (h-chymase) using an original system of expression in Pichia pastoris (Nakakubo et al., 2000), whereby recombinant h-chymase (rh-chymase) was secreted as a mature form with the correct N-terminal amino acid sequence and was easily purified. In the course of investigation of secretory rh-chymase, we also found large amounts of chymase to be present in insoluble form in the transformant cell. Although the cellular rh-chymase had no proteolytic activity, its chymotryptic activity was restored in a reconstitution process utilizing guanidine and glutathione. As with secretory rh-chymase, efficient purification was possible by heparin affinity chromatography. The purified cellular rh-chymase showed the same mobility as secretory rh-chymase in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before and after deglycosylation. N-terminal amino acid sequence analysis revealed that the signal peptide had been correctly removed. K(m) value (5.93 mM), as well as pH profile and inhibition profile toward protease inhibitors of reconstituted cellular rh-chymase, indicated that the rh-chymase enzymatically closely resembles native h-chymase. Furthermore, it showed a greatly restricted proteolytic activity towards Ang I, and formed Ang II without the further cleavage which is a feature of h-chymase. It was thus found that the insoluble rh-chymase stored in the cells could be solubilized and reconstituted to give the same structure as h-chymase, not only in terms of enzyme active site but also of substrate recognition site.