Woo-Suk Jung

A highly efficient sorbitol dehydrogenase from Gluconobacter oxydans G624 and improvement of its stability through immobilization

A sorbitol dehydrogenase (GoSLDH) from Gluconobacter oxydans G624 (G. oxydans G624) was expressed in Escherichia coli BL21(DE3)-CodonPlus RIL. The complete 1455-bp codon-optimized gene was amplified, expressed, and thoroughly characterized for the first time. GoSLDH exhibited Km and kcat values of 38.9 mM and 3820 s−1 toward L-sorbitol, respectively. The enzyme exhibited high preference for NADP+ (vs. only 2.5% relative activity with NAD+). GoSLDH sequencing, structure analyses, and biochemical studies, suggested that it belongs to the NADP+-dependent polyol-specific long-chain sorbitol dehydrogenase family. GoSLDH is the first fully characterized SLDH to date, and it is distinguished from other L-sorbose-producing enzymes by its high activity and substrate specificity. Isothermal titration calorimetry showed that the protein binds more strongly to D-sorbitol than other L-sorbose-producing enzymes, and substrate docking analysis confirmed a higher turnover rate. The high oxidation potential of GoSLDH for D-sorbitol was confirmed by cyclovoltametric analysis. Further, stability of GoSLDH significantly improved (up to 13.6-fold) after cross-linking of immobilized enzyme on silica nanoparticles and retained 62.8% residual activity after 10 cycles of reuse. Therefore, immobilized GoSLDH may be useful for L-sorbose production from D-sorbitol.

Phlorofucofuroeckol-A, a potent inhibitor of aldo-keto reductase family 1 member B10, from the edible brown alga Eisenia bicyclis

Aldo-keto reductase family 1 member B10 (AKR1B10) belongs to a superfamily of NADPH-dependent aldo-keto reductases and is considered a biomarker of several cancers. Inhibition of recombinant human AKR1B10 (rhAKR1B10) was assayed using 31 seaweed extracts, among which, an Eisenia bicyclis extract was selected for further study. To identify the compounds in E. bicyclis responsible for inhibitory effects on rhAKR1B10, five compounds were isolated by bioactivity-guided fractionation and isolation. Among them, phlorofucofuroeckol-A (PFF-A), isolated from an ethyl acetate fraction, exhibited the greatest inhibition of rhAKR1B10. The inhibitory rate of PFF-A against rhAKR1B10 was 61.41% at 10 μM, with an IC50 of 6.22 μM. Enzyme kinetic analyses revealed non-competitive inhibition with a KD of 2.76 μM. These results indicate that PFF-A from E. bicyclis may be a promising anticancer agent.

Characterization of a Mannose-6-Phosphate Isomerase from Bacillus amyloliquefaciens and Its Application in Fructose-6-Phosphate Production

The BaM6PI gene encoding a mannose-6-phosphate isomerase (M6PI, EC 5.3.1.8) was cloned from Bacillus amyloliquefaciens DSM7 and overexpressed in Escherichia coli. The enzyme activity of BaM6PI was optimal at pH and temperature of 7.5 and 70°C, respectively, with a kcat/Km of 13,900 s-1 mM-1 for mannose-6-phosphate (M6P). The purified BaM6PI demonstrated the highest catalytic efficiency of all characterized M6PIs. Although M6PIs have been characterized from several other sources, BaM6PI is distinguished from other M6PIs by its wide pH range and high catalytic efficiency for M6P. The binding orientation of the substrate M6P in the active site of BaM6PI shed light on the molecular basis of its unusually high activity. BaM6PI showed 97% substrate conversion from M6P to fructose-6-phosphate demonstrating the potential for using BaM6PI in industrial applications.

Chemiresistive Sensor Array Based on Semiconducting Metal Oxides for Environmental Monitoring

We present gas sensing performance based on 22 sensor array with four different elements (TiO2, SnO2, WO3 and In2O3 thin films) fabricated by rf sputter. Each thin film was deposited onto the selected SiO2/Si substrate with Pt interdigitated electrodes (IDEs) of 5 m spacing which were fabricated on a SiO2/Si substrate using photolithography and dry etching. For 5 ppm NO2 and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, 22 sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multi- functional smart sensors for environmental monitoring.

Crystal structure and substrate specificity of D-galactose-6-phosphate isomerase complexed with substrates.

D-Galactose-6-phosphate isomerase from Lactobacillus rhamnosus (LacAB; EC 5.3.1.26), which is encoded by the tagatose-6-phosphate pathway gene cluster (lacABCD), catalyzes the isomerization of D-galactose-6-phosphate to D-tagatose-6-phosphate during lactose catabolism and is used to produce rare sugars as low-calorie natural sweeteners. The crystal structures of LacAB and its complex with D-tagatose-6-phosphate revealed that LacAB is a homotetramer of LacA and LacB subunits, with a structure similar to that of ribose-5-phosphate isomerase (Rpi). Structurally, LacAB belongs to the RpiB/LacAB superfamily, having a Rossmann-like αβα sandwich fold as has been identified in pentose phosphate isomerase and hexose phosphate isomerase. In contrast to other family members, the LacB subunit also has a unique α7 helix in its C-terminus. One active site is distinctly located at the interface between LacA and LacB, whereas two active sites are present in RpiB. In the structure of the product complex, the phosphate group of D-tagatose-6-phosphate is bound to three arginine residues, including Arg-39, producing a different substrate orientation than that in RpiB, where the substrate binds at Asp-43. Due to the proximity of the Arg-134 residue and backbone Cα of the α6 helix in LacA to the last Asp-172 residue of LacB with a hydrogen bond, a six-carbon sugar-phosphate can bind in the larger pocket of LacAB, compared with RpiB. His-96 in the active site is important for ring opening and substrate orientation, and Cys-65 is essential for the isomerization activity of the enzyme. Two rare sugar substrates, D-psicose and D-ribulose, show optimal binding in the LacAB-substrate complex. These findings were supported by the results of LacA activity assays.

Oxygen Vacancy Effects of Two-Dimensional Electron Gas in SrTiO 3 /KNbO 3 Hetero Structure

Abstract The discovery of a two-dimensional electron gas (2DEG) in LaAlO 3 (LAO)/SrTiO 3 (STO) heterostructure has stimulated intenseresearch activity. We suggest a new structure model based on KNbO 3 (KNO) material. The KNO thin films were grown on TiO 2 -terminated STO substrates as a p-type structure (NbO 2 /KO/TiO 2 ) to form a two-dimensional hole gas (2DHG). The STO thin films weregrown on KNO/TiO 2 -terminated STO substrates as an n-type structure to form a 2DEG. Oxygen pressure during the deposition of theKNO and STO thin films was changed so as to determine the effect of oxygen vacancies on 2DEGs. Our results showed conductingbehavior in the n-type structure and insulating properties in the p-type structure. When both the KNO and STO thin films were depositedon a TiO 2 -terminated STO substrate at a low oxygen pressure, the conductivity was found to be higher than that at higher oxygenpressures. Furthermore, the heterostructure formed at various oxygen pressures resulted in structures with different current values. AnSTO/KNO heterostructure was also grown on the STO substrate, without using the buffered oxide etchant (BOE) treatment, so as toconfirm the effects of the polar catastrophe mechanism. An STO/KNO heterostructure grown on an STO substrate without BOEtreatment did not exhibit conductivity. Therefore, we expect that the mechanics of 2DEGs in the STO/KNO heterostructures are governedby the oxygen vacancy mechanism and the polar catastrophe mechanism.

Investigation of piezoelectric ceramic size effect for miniaturing the piezoelectric energy harvester

Energy harvesting from the vibration through the piezoelectric effect has been studied for powering the small wireless sensor nodes. As piezoelectric uni-morph cantilever structure can transfer low vibration to large displacement, this structure was commonly deployed to harvest electric energy from vibrations. Through our previous results, when stress was applied on the cantilever, stress was concentrated on the certain point of the ceramic of the cantilever. In this study, for miniaturing the energy harvester, we investigated how the size of ceramics and the stress distribution in ceramic affects energy harvester characteristics. Even though the area of ceramic was 28.6 % decreased from to , both samples showed almost same maximum power of 0.45 mW and the electro-mechanical coupling factor () of 14 % as well. This result indicated that should be preferentially considered to generate high power with small size energy harvester.

Dynamic properties of an omni-directional piezoelectric motor for precision position control

A piezoelectric motor capable of omni-directional movements has been developed to apply for robot joints, eyes, and precision positioning stage. The piezoelectric actuator has a simple structure of a cone type consisting of two piezoelectric ring-typed ceramics with electrodes divided into four segments and stainless steel elastic bodies. Before manufacturing the piezoelectric motor, the admittance characteristics and displacements of the actuator as a function of frequency were simulated. Elliptical motions of the actuator were created at several frequencies between the longitudinal and transverse resonance frequencies. The actual motor with alumina ball exhibited nice performance using a driving circuit with two rotary encoders and a PID controller. The moving element was omni-directionally operated at a driving frequency of 53.8 kHz and an output voltage of 280 V(p-p). The developed motor enables the moving element to move to a desired position with a resolution of 1.2 degrees/pulse, an angular velocity of 4 rad/s, and a thrust force of 200 g.

Design and analysis of omni-directional linear piezoelectric actuator

In this paper, we present design and analysis of the omni-directional linear piezoelectric actuator which was consisted of one actuator using the half-wave vibrator. Through calculating vibration speeds on each sector of the actuator, the displacement of contact point of the actuator is theoretically confirmed to be about 33 nm. To confirm an applicable possibility of omni-directional linear piezoelectric actuator, elliptical motion for linear movement, displacement of the tip, changing directions and admittance characteristics are simulated by ATILA. Compared with theoretical result, we obtained similar data with displacement of 32.5 nm at contact point. And then the actuator is simulated elliptical trajectories for linear motions and changing directions according to combination of input signal.

Design of electronic tongue using IEEE 1451.2

The IEEE 1451 publication are available, this standard defines interface between sensor and processor, and plug and play in processor is possible. Also, Intelligence of sensor was possible because sensor includes transducer electronic data sheet (TEDS). In IEEE 1451 standards, IEEE 1451.4 is suitable standard in single sensor, and IEEE 1451.2 is suitable standard in multi-sensors (array sensor). In this paper, apply IEEE 1451 to electronic tongue system. In the case of electronic tongue system, because array sensor is used, it is that complex and difficult to apply IEEE 1451.4 that is standard for single sensor. In this paper, apply IEEE 1451.2 for array sensor to design of electronic tongue system. Communication interface method of IEEE 1451.2 for electronic tongue system is presented, and implemented TEDS of electronic tongue system.