Arabidopsis β1,2-xylosyltransferase: substrate specificity and participation in the plant-specific N-glycosylation pathway

β1,2-Xylosyltransferase (XYLT) is a plant-specific glycosyltransferase that contributes to the biosynthesis of N-glycoproteins in plants. However, the specificity of XYLT for N-glycans has not yet been completely clarified. To gain insights into the function of XYLT in the plant N-glycosylation pathway, we examined the acceptor substrate specificity of recombinant Arabidopsis XYLT (AtXYLT) using 2-aminopyridine-labeled N-glycans as the substrates and confirmed the N-glycans of Arabidopsis xylt mutant. Recombinant AtXYLT expressed in insect cells required the β1,2-linked N-acetylglucosamine (GlcNAc) residue at the nonreducing terminus of the α1,3-branched mannose (Man) residue (GlcNAcβ1,2-Manα1,3-Man; GNM3B) for activity. However, AtXYLT showed decreased activity with substrates that contained α1,3-fucose at the chitobiose core-GlcNAc or a terminal GlcNAc at the α1,6-branched Man residue of GlcNAcβ1,2-Man (GlcNAcβ1,2-Manα1,6-Man; GNM3A), whose ratios were 10% and 50% of the optimal substrate, GNM3B, respectively. Moreover, AtXYLT did not show any activity in the transfer of the Xyl residue to N-glycans that contained a mammalian-type β1,4-linked galactose (Gal) residue at the nonreducing terminus of GlcNAcβ1,2-Man. These results indicate that a β1,2-linked GlcNAc residue at the nonreducing terminus of an α1,3-branched Man residue is necessary for AtXYLT activity and that mammalian-type β1,4-linked Gal residue(s) on the same branch completely inhibit(s) the activity. Furthermore, N-glycan analysis showed that approximately 30% of the N-glycans carry the Xyl residue in the wild type. These findings suggest that AtXYLT acts on protein-bound N-glycans prior to α1,3-fucosyltransferase and mannosidase II in planta.     

Instrument for Measuring the Body Mass of Astronauts Under Microgravity Conditions

An improved prototype of the space scale, which has been proposed as a practical and lightweight instrument for measuring the body mass of astronauts under microgravity conditions in the International Space Station (ISS), has been developed. A prominent feature of the proposed instrument is the use of a bungee cord as the source of force. This results in a simple, lightweight, and compact structure of the instrument. It also results in a large displacement during the measurement and then the reduction of the effect of change in subject posture. The feasibility of the prototype design has been evaluated by quantifying the body mass of a human subject in a parabolic flight test. The present and future statuses of the space scale are discussed.     

InGaAs quantum dots formed in tetrahedral-shaped recesses on GaAs (111)B grown by metalorganic chemical vapor deposition

Novel semiconductor quantum dots (QDs), grown in tetrahedral-shaped recesses (TSRs) formed on a (111)B GaAs substrate, are described from both material science and device application points of view. After explaining the fabrication procedure for TSRs, growth of InGaAs QDs and their optical properties are explained. It is revealed that an InGaAs QD of indium-rich chemical composition is formed spontaneously at the bottom of each TSR. The mechanism of the QD formation is discussed in detail. It is proved from magneto-photoluminescence that the QDs actually have optical properties peculiar to zero-dimensional confinement. Several experimental results indicating excellent growth controllability of the QDs are presented. Finally, recent challenges to apply the QDs to electronic memory devices are reported. Two kinds of devices, where the position of individual QD is artificially controlled, are proposed for the first time and the preliminary experimental results are explained.     

Optimal Structure for High‐Performance and Low‐Contact‐Resistance Organic Field‐Effect Transistors Using Contact‐Doped Coplanar and Pseudo‐Staggered Device Architectures

A low contact resistance achieved on top‐gated organic field‐effect transistors by using coplanar and pseudo‐staggered device architectures, as well as the introduction of a dopant layer, is reported. The top‐gated structure effectively minimizes the access resistance from the contact to the channel region and the charge‐injection barrier is suppressed by doping of iron(III)trichloride at the metal/organic semiconductor interface. Compared with conventional bottom‐gated staggered devices, a remarkably low contact resistance of 0.1–0.2 kΩ cm is extracted from the top‐gated devices by the modified transfer line method. The top‐gated devices using thienoacene compound as a semiconductor exhibit a high average field‐effect mobility of 5.5–5.7 cm² V^?1 s^?1 and an acceptable subthreshold swing of 0.23–0.24 V dec^?1 without degradation in the on/off ratio of ≈10⁹. Based on these experimental achievements, an optimal device structure for a high‐performance organic transistor is proposed.     

Forming semiconductor/dielectric double layers by one-step spin-coating for enhancing the performance of organic field-effect transistors

We report one-step formation of the gate dielectric and conduction channel for enhancing the performance of organic field effect transistors (OFETs). The resulting OFET with the semiconductor/dielectric bi-layers spun in ambient conditions exhibits μ_FET up to 1.6 cm²/V s and on–off ratio higher than 10⁶, no additional treatment needed. Contact angle measurements and absorption spectra reveals that a well-defined semiconductor-top and dielectric-bottom film form after spin-coating the mixture of the two components, which is due to the surface induced self-organized phase separation. Compared to the single layer semiconductor film, the staggered film exhibits over 5 times higher mobility and nearly 90% reduced hysteresis in OFET. The higher performance is attributed to the simultaneous optimization in the dielectric interface and semiconductor crystallization. The approach is significant for the fabrication of low cost, easy processed and high performance OFETs.     

Equations for spectrophotometric determination of relative concentrations of myoglobin derivatives in aqueous tuna meat extracts

The percentage of metmyoglobin (%metMb) in aqueous meat extracts of bigeye and bluefin tuna and beef samples were estimated using previously reported equations derived from the absorption spectra of horse Mb. The results demonstrate that in an aqueous extract, the difference in %metMb estimated by the different equations was negligible for beef samples. Conversely, in an aqueous tuna extract, different %metMb values were obtained with the different equations. The discrepancy in the tuna sample results might be due to differences in absorption spectra for horse and tuna Mb. Therefore, a new set of equations derived from the absorption spectra of bigeye tuna Mb, reported by Matsuura and Hashimoto (1955), was established. The accuracy of the proposed equations was compared with the cyanmetmyoglobin (cyanmetMb) method. The results show that the total Mb concentrations estimated by our proposed equations were in good agreement with the results obtained by the conventional cyanmetMb method (R² = 0.984). Therefore, the new set of proposed equations is valid for the spectrophotometric determination of the relative proportions of Mb derivatives and total Mb concentration in aqueous tuna meat extracts.     

Characteristics and oil absorption of deep‐fat fried dough prepared from ball‐milled wheat flour

BACKGROUND: High levels of oil in fried products has been recognized as causing health problems. The formation of microstructure during frying is one factor that influences oil absorption. Above the glass transition temperature (T_g), the physical properties of a polymer influences the formation of structure. The ball‐milling process changes the physicochemical properties of wheat flour constituents. The present study investigated the effects of physicochemical changes in wheat flour by the ball‐milling process on structure formation and oil absorption in wheat flour dough model. RESULTS: Dough samples were made from wheat flour that had been ball‐milled for 0 to 10 h and then fried in frying oil at 150 °C for 1–7 min. Thermal properties of wheat flour, structure alteration, and textural properties of fried samples were evaluated. As compared with samples made of non‐milled flour, samples made from milled flour had smaller pores and higher oil absorption. The fracture force of a fried sample prepared from non‐milled flour was lower than that of a sample prepared from milled flour. CONCLUSION: Ball‐milling affected the microstructure formation in fried wheat flour dough, and subsequently oil absorption. The crispness of a sample prepared from non‐milled wheat flour is higher than that of a sample prepared from ball‐milled wheat flour. This may be due not only to a plasticization effect, but may also be dependent on microstructure. Copyright © 2008 Society of Chemical Industry