Stabilization of Hydroxynitrile Lyases from Two Variants of Passion Fruit,Passiflora edulis Sims and Passiflora edulis Forma flavicarpa,by C-Terminal Truncation

Because the synthesis of chiral compounds generally requires a broad range of substrate specificity and stable enzymes, screening for better enzymes and/or improvement of enzyme properties through molecular approaches is necessary for sustainable industrial development. Herein, the discovery of unique hydroxynitrile lyases (HNLs) from two species of passion fruits, Passiflora edulis forma flavicarpa (yellow passion fruit, PeHNL-Ny) and Passiflora edulis Sims (purple passion fruit, PeHNL-Np), isolated and purified from passion fruit leaves is reported. These are the smallest HNLs (comprising 121 amino acids). Amino acid sequences of both enzymes are 99 % identical; there is a difference of one amino acid in a consensus sequence. PeHNL-Np has an Ala residue at position 107 and is nonglycosylated at Asn105. Because it was confirmed that natural and glycosylated PeHNL-Ny showed superior thermostability, pH stability, and organic tolerance to that of PeHNL-Np, it has been speculated that protein engineering around the only glycosylation site, Asn105, located at the C-terminal region of PeHNL-Ny, might contribute to the stabilization of PeHNL. Therefore, the focus is on improved stability of the nonglycosylated PeHNL by truncating its C-terminal region. The C-terminal-truncated PeHNLΔ₁₀₇ was obtained by truncating 15 amino acids from the C terminus followed by expression in Escherichia coli. PeHNLΔ₁₀₇ expressed in E. coli was not glycosylated, and showed improved thermostability, solvent stability, and reusability similar to that of the wild-type glycosylated form of PeHNL expressed in Pichia pastoris. These data reveal that the lack of the high-flexibility region at the C terminus of PeHNL might be a possible reason for improving the stability of PeHNL.     

Segregation and Local Structure at Grain Boundaries in SiO2-Doped Tetragonal ZrO2 Polycrystalline Materials

SiO₂ doping in Y₂O₃ stabilized tetragonal ZrO₂ (TZP) materials introduced significant change in mechanical properties around 0.3 wt.% doping level [1]. In order to understand the influence of grain boundary structure and chemistry by doping, high purity undoped and SiO₂-doped 3Y-TZP samples were studied using high-resolution and analytical TEM. Typical grain boundary structures are different for the two types of samples, while amorphous film was not observed at most grain boundaries. A new EDS analysis method was introduced to detect the weak Si and Y signals which overlap with the predominent Zr peaks. It revealed that Si segregation to the grain boundary saturates at 12 at./nm² (or 1.5 monolayer of SiO₂) when the SiO₂ doping level reached and surpassed 0.3 wt.%. It is the segregated atoms which enhanced the grain boundary diffusivity and therefore altered the deformation mechanism.     

Compression Deformation Mechanism of Silicon Carbide: I, Fine-Grained Boron- and Carbon-Doped β-Silicon Carbide Fabricated by Hot Isostatic Pressing

The deformation behavior of boron- and carbon-doped β-silicon carbide (B,C-SiC) with an average grain size of 260 ± 18 nm containing 1 wt% boron was investigated by compression testing at elevated temperatures. Extensive grain growth during deformation was observed. The stress–strain curves were compensated for grain growth by assuming power-law type of dependence on grain size and strain rate. The stress exponent n was ∼1.3 and the grain size exponent p was ∼2.7 at temperatures ranging from 1593° to 1758°C. The apparent activation energy of deformation Q _d was ∼760 kJ/mol, which was lower than the activation energy for lattice diffusion of silicon and carbon in SiC and higher than that for grain-boundary diffusion of carbon in SiC. These results suggest that the deformation mechanism of the fine-grained B,C-SiC is grain-boundary sliding accommodated by the grain-boundary diffusion.     

Difference in environmental degradability between poly(ethylene succinate) and poly(3-hydroxybutyrate)

A chemosynthetic aliphatic polyester, poly(ethylene succinate) (PESu), was degraded by a poly(3-hydroxybutyrate) (P(3HB)) depolymerase in vitro. While P(3HB) exhibited good biodegradability in all environments, PESu hardly underwent biodegradation in a marine environment. To understand the difference in environmental degradability between PESu and P(3HB), we investigated the distribution of P(3HB)- and PESu-degrading microbes in various environments. PESu-degrading microbes were never detected in marine environments. PESu-degrading bacteria isolated from various environments in this study belonged to the phyla Firmicutes and Proteobacteria. Most PESu-degrading bacterial isolates could not degrade P(3HB), suggesting that PESu was not degraded by P(3HB) depolymerase in actual environments. In addition, all bacterial isolates that were screened for P(3HB) degrading activity from various environments in this study did not degrade PESu, suggesting that PESu does not induce P(3HB) depolymerase in their bacteria and P(3HB)-degrading bacteria are not involved in biodegradation of PESu in actual environments. Taken together, these results could be related with the low biodegradability of PESu in marine environments.     

Adaptive control of maximum thermal stress in a smart piezocomposite disk

In this paper, an adaptive control problem of the maximum thermal stress in a smart composite disk is analyzed. The disk consists of a transversely isotropic structural layer onto which piezoelectric sensor and actuator layers are bonded. It is considered that an unknown heating temperature distribution acts on the structural layer and a thermally induced voltage distribution is measured on the sensor layer. The unknown heating temperature distribution is inferred from the knowledge of the measured voltage distribution. Applied voltages to electrodes arranged on every actuator layer are determined by optimization so that the maximum thermal stress in the structural layer is minimized and stress constraints imposed on the piezoelectric layers are satisfied. Finally, the suppression ratio of the maximum thermal stress is discussed based on numerical results.     

The study of activity median aerodynamic diameter using imaging plate technique for assessment of effective dose from radon and its decay products

The indoor workplace environment was evaluated for exposure to radon and its decay products at two Universities in two metropolises of Japan. The mean radon concentrations in Nagoya University (NU) and Hokkaido University (HU) were 16.7 Bq m(-3) and 18.0 Bq m(-3), respectively. Activity median aerodynamic diameter (AMAD) of particles at NU ranged from 172 nm approximately 205 nm and at HU from 186 nm approximately 300 nm. Estimated effective doses for five usual sites of NU by ICRP approach was 0.15 mSvy(-1) approximately 0.76 mSvy(-1) and by UNSCEAR approach was 0.05 mSvy(-1) approximately 0.24 mSvy(-1). The effective dose for the same of HU by ICRP 66 approach was 0.16 mSvy(-1) approximately 0.79 mSvy(-1) and by UNSCEAR 2000 approach was 0.05 mSv y(-1) to 0.26 mSv y(-1). The two approaches differs on an average by a factor 2.3- approximately 4.7. The AMAD of obtained particle size distribution at NU has an average total deposition of 23% in human respiratory tract and 20% at HU.     

Kinetic parameters for anodic oxidation of hypochlorite ion on Pt and Pt oxide electrodes in alkaline solution

Kinetic parameters for the anodic oxidation of hypochlorite ion have been determined by means of normal pulse voltammetry by using a platinum disk as the working electrode. By using the working electrode that formed an oxide film by electrochemical pretreatment, the effect of the lattice oxygen of the surface oxide on the reaction was also examined. The measurement results were analyzed by the classical method, and then the analytical results were evaluated by digital simulation. The normal pulse voltammogram of the hypochlorite ion showed quasi-reversible oxidation waves. The apparent rate constant was calculated to be 5.0-8.1 × 10⁻⁴ cm s⁻¹, depending on the electrode surface state. At the low-concentration range of <4.0 mg Cl dm⁻³, the oxidation current was concentration dependent at the cathodically polarized electrode, while it became independent after the anodic polarization.     

Strain selection and scale-up fermentation for FR901379 acylase production by Streptomyces sp. no. 6907

Micafungin (FK463) is a widely used treatment for life-threatening, deep-seated fungal infections. It is an echinocandin-like lipopeptide derived from the chemical modification of deacylated FR901379, a type of lipopeptide antibiotic produced by Coleophoma empetri F-11899. The palmitoyl moiety of FR901379 is deacylated by FR901379 acylase produced by Streptomyces sp. no. 6907. In this study, our goal was to generate an improved strain of Streptomyces sp. no. 6907 capable of hyperproducing the FR901379-acylase enzyme. To accomplish this goal, modified strains of Streptomyces sp. no. 6907 were generated using UV-irradiation mutagenesis, and strain selection was performed using an agar-plate screening method to efficiently select an acylase-hyperproducing strain. Three marker indices were shown to correlate with elevated acylase production: decreased candidacidal activity of FR901379, decreased proteolytic activity on skim milk, and phenotypic characteristics. Cloning and subsequent sequencing of the acylase gene from the hyperproducing mutant revealed no mutations in either the acylase structural gene or the 5'-flanking region required for gene expression. The growth medium was also modified to maximize acylase production. We successfully increased acylase activity approximately 65-fold, compared with the original growth conditions (wild strain cultured in the original unmodified medium). To minimize formation of excess foam during the fermentation process, we optimized the parameters of agitation speed, as calculated from the discharge flow rate. Using our improved strain and the optimized medium and growth conditions, we have developed an improved and highly reproducible method for stable large-scale production of FR901379-acylase.     

Recent plant experience and research into fireside corrosion in Japan

The increasing use of heavy oil as a fuel in power stations has given rise to intensified research in the field of fireside corrosion in Japan. The problems which have to be tackled are described in terms of experiences gained in the operation of oil and coal fired boilers. The main types of damage encountered are nonuniform wastage of tubes in connection with carburization. In this context significant interdependences have been found in connection with coal deposition (especially sodium and sulphur contents). On the basis of this experiences and of the results of corrosion tests in the laboratory and in the field it has been found that the measure offering the best prospect for corrosion control might be the use of coextruded tubing which would allow a combination of high corrosion resistance and high creep strength. In addition to that some modified alloys (e.g. Alloy 800 H, CR 30 A or NF709) offer an interesting potential whereby the high chromium content (more than 20%) is the main criterium.     

Effects of solute ion and grain size on superplasticity of ZrO2 polycrystals

The deformation of ZrO₂ polycrystals containing 2 to 8 mol% Y₂O₃ or 12 mol% CeO₂ were investigated by uniaxial tension and tensile creep tests at elevated temperatures. It was found that there were two deformation mechanisms. The stress exponent was close to 2 for the finegrained materials (less than 1 m), but the exponent decreased with increasing grain size. This behaviour was analysed using a model based on grain-boundary sliding with diffusion accommodation, in which the diffusion creep controlled by interface-reaction and that controlled by diffusion of cations were incorporated. The diffusion coefficient of cations was greatly affected by the concentration of the solute ions. It was observed that there was a negative correlation between interface-reaction rate and Y₂O₃ concentration.