Comparative Modeling and Analysis of Extremophilic D-Ala-D-Ala Carboxypeptidases
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Elizabeth M. Diessner↗
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Results for “AlAs”
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The yeast ALA synthase C‐terminus positively controls enzyme structure and function
Abstract 5‐Aminolevulinic acid synthase (ALAS) is a pyridoxal 5′‐phosphate (PLP)‐dependent enzyme that catalyzes the first and rate‐limiting step of heme biosynthesis in α‐proteobacteria and several non‐plant eukaryotes. All ALAS homologs contain a highly conserved catalytic core, but eukaryotes also have a unique C‐terminal extension that plays a role in enzyme regulation. Several mutations in this region are implicated in multiple blood disorders in humans. In Saccharomyces cerevisiae ALAS (Hem1), the C‐terminal extension wraps around the homodimer core to contact conserved ALAS motifs proximal to the opposite active site. To determine the importance of these Hem1 C‐terminal interactions, we determined the crystal structure of S. cerevisiae Hem1 lacking the terminal 14 amino acids (Hem1 ΔCT). With truncation of the C‐terminal extension, we show structurally and biochemically that multiple catalytic motifs become flexible, including an antiparallel β‐sheet important to Fold‐Type I PLP‐dependent enzymes. The changes in protein conformation result in an altered cofactor microenvironment, decreased enzyme activity and catalytic efficiency, and ablation of subunit cooperativity. These findings suggest that the eukaryotic ALAS C‐terminus has a homolog‐specific role in mediating heme biosynthesis, indicating a mechanism for autoregulation that can be exploited to allosterically modulate heme biosynthesis in different organisms.
59 BASIC BIOLOGICAL SCIENCES↗
AmeriFlux FLUXNET-1F US-xPU NEON Pu'u Maka'ala Natural Area Reserve (PUUM)
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-xPU NEON Pu'u Maka'ala Natural Area Reserve (PUUM). This is the FLUXNET version of the carbon flux data for the site US-xPU NEON Pu'u Maka'ala Natural Area Reserve (PUUM) produced by applying the standard ONEFlux (1F) software. Site Description - NEON's PUUM field site is located in the Pu'u Maka'ala Natural Area Reserve (NAR) on the eastern side of Hawaii’s “Big Island,” managed by the Hawaii Division of Forestry and Wildlife (DOFAW). More than 18,000 acres in size, the NAR is home to a rainforest with many native species, some of them endangered. It was established to protect some of the Big Island’s best wet native forest and unique geologic features.
Network), NEON (National Ecological Observatory [N↗
AmeriFlux US-xPU NEON Pu'u Maka'ala Natural Area Reserve (PUUM)
This is the AmeriFlux version of the carbon flux data for the site US-xPU NEON Pu'u Maka'ala Natural Area Reserve (PUUM). Site Description - NEON's PUUM field site is located in the Pu'u Maka'ala Natural Area Reserve (NAR) on the eastern side of Hawaii’s “Big Island,” managed by the Hawaii Division of Forestry and Wildlife (DOFAW). More than 18,000 acres in size, the NAR is home to a rainforest with many native species, some of them endangered. It was established to protect some of the Big Island’s best wet native forest and unique geologic features.
Network), NEON (National Ecological Observatory↗
Preparation of visible-light-emitting p-n junctions in AlAs
Visible light-emitting p-n junctions formed in AlAs via Zn diffusion into single crystal n- type vapor grown AlAs layers
Ettenberg, M.↗
Enhanced indirect optical absorption in AlAs and GaP.
Measurement and analysis of indirect interband optical absorption in GaP. Deviations from a simple indirect absorption law are shown to be consistent with those given by a model which takes into account both the variation of the energy denominators with photon energy and indirect absorption to higher-energy conduction-band valleys. The analysis of the GaP data indicates that such an analysis on data of limited absorption-constant range can provide reasonably accurate values of the direct band gap. The value of the direct band gap best fitting this model for AlAs at 6 K is 3.13 eV. In GaP and AlAs there is evidence of a higher set of extrema giving rise to an additional indirect absorption component 0.34 and 0.20 eV, respectively, above that due to the lowest-energy conduction-band minima. The strength of the absorption due to these higher-energy valleys indicates that they contain states of X sub 3 symmetry.
Dumke, W. P.↗
The Simplified Aircraft-Based Paired Approach With the ALAS Alerting Algorithm
This paper presents the results of an investigation of a proposed concept for closely spaced parallel runways called the Simplified Aircraft-based Paired Approach (SAPA). This procedure depends upon a new alerting algorithm called the Adjacent Landing Alerting System (ALAS). This study used both low fidelity and high fidelity simulations to validate the SAPA procedure and test the performance of the new alerting algorithm. The low fidelity simulation enabled a determination of minimum approach distance for the worst case over millions of scenarios. The high fidelity simulation enabled an accurate determination of timings and minimum approach distance in the presence of realistic trajectories, communication latencies, and total system error for 108 test cases. The SAPA procedure and the ALAS alerting algorithm were applied to the 750-ft parallel spacing (e.g., SFO 28L/28R) approach problem. With the SAPA procedure as defined in this paper, this study concludes that a 750-ft application does not appear to be feasible, but preliminary results for 1000-ft parallel runways look promising.
Perry, Raleigh B.↗
Materials Data on AlAs by Materials Project
AlAs is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Al3+ is bonded to six equivalent As3- atoms to form a mixture of edge, corner, and face-sharing AlAs6 octahedra. The corner-sharing octahedral tilt angles are 49°. All Al–As bond lengths are 2.65 Å. As3- is bonded in a 6-coordinate geometry to six equivalent Al3+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on AlAs by Materials Project
AlAs is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Al3+ is bonded to four equivalent As3- atoms to form corner-sharing AlAs4 tetrahedra. All Al–As bond lengths are 2.48 Å. As3- is bonded to four equivalent Al3+ atoms to form corner-sharing AsAl4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on AlAs by Materials Project
AlAs is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Al3+ is bonded to four equivalent As3- atoms to form corner-sharing AlAs4 tetrahedra. There are three shorter (2.48 Å) and one longer (2.49 Å) Al–As bond lengths. As3- is bonded to four equivalent Al3+ atoms to form corner-sharing AsAl4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on AlAs by Materials Project
AlAs is High Pressure Cadmuum Telluride structured and crystallizes in the orthorhombic Pmm2 space group. The structure is three-dimensional. Al3+ is bonded in a linear geometry to two equivalent As3- atoms. Both Al–As bond lengths are 2.67 Å. As3- is bonded to two equivalent Al3+ and four equivalent As3- atoms to form a mixture of distorted corner and edge-sharing AsAl2As4 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. All As–As bond lengths are 2.72 Å.
36 MATERIALS SCIENCE↗
Materials Data on AlAs by Materials Project
AlAs is Halite, Rock Salt structured and crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Al3+ is bonded to six equivalent As3- atoms to form a mixture of corner and edge-sharing AlAs6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Al–As bond lengths are 2.65 Å. As3- is bonded to six equivalent Al3+ atoms to form a mixture of corner and edge-sharing AsAl6 octahedra. The corner-sharing octahedral tilt angles are 0°.
36 MATERIALS SCIENCE↗
Correlated States of Two-dimensional Electron Systems in AlAs Quantum Wells
Two-dimensional (2D) carrier systems confined to modulation-doped semiconductor hetero-structures provide a nearly ideal testing ground for exploring new physical phenomena. At low temperatures and in the presence of a strong magnetic field, these systems exhibit fascinating, often unexpected, many-body states, arising from the strong electron-electron interaction. In our work, we studied various many-body states of different 2D systems. These included 2D electron and hole systems confined to GaAs and also to AlAs quantum wells, including wide quantum wells where the charge distribution is bilayer like. We observed and reported new phenomena in these systems, including new (even-denominator) fractional quantum Hall states, Wigner crystal solid phases, and composite fermion compressible states.
36 MATERIALS SCIENCE↗
Thermal expansion of AlAs
Lattice parameter and thermal expansion of AlAs as function of temperature, indicating lattice match at 900 C with GaAs
Ettenberg, M.↗
Solidus boundary in the InAs-AlAs pseudobinary system
InAs-AlAs pseudobinary system solidus boundary determination from pellet phase diagram
Foster, L. M.↗
Structure variation of the index of refraction of GaAs-AlAs superlattices and multiple quantum wells
A detailed calculation of the index refraction of various GaAs-AlAs superlattices is presented for the first time. The calculation is performed by using a hybrid approach which combines the k-p method with the pseudopotential technique. Appropriate quantization conditions account for the influence of the superstructures on the electronic properties of the systems. The results of the model are in very good agreement with the experimental data. In comparison with the index of refraction of the corresponding AlGaAs alloy, characterized by the same average mole fraction of Al, the results indicate that the superlattice index of refraction values attain maxima at the various quantized transition energies. For certain structures the difference can be as large as 2 percent. These results suggest that the waveguiding and dispersion relation properties of optoelectronic devices can be tailored to design for specific optical application by an appropriate choice of the superlattice structure parameters.
Kahen, K. B.↗
Atmospheric Lyman-Alpha Emissions (ALAE)
The Atmospheric Lyman-Alpha Emissions (ALAE) experiment which is designed to measure atomic hydrogen and deuterium in the terrestrial atmosphere is described. The development of the instrument is a joint effort of the Service d'Aeronomie du CNRS in France and the Institut d'Aeronomie Spatiale in Belgium. This experiment will be part of the atmospheric science research payload flown on the Atmospheric Laboratory for Applications and Science (ATLAS 1) NASA mission planned for late 1990.
Bertaux, J. L.↗
Simulation of GaAs cluster formation on GaAs(00-1), AlAs(00-1), Si(001), and As1/Si(001) surfaces
Recently developed semiempirical potential energy functions for the Ga-As-Si and Ga-As-Al systems have been applied here to determine the excess formation energy for GaAs clusters on GaAs(00-1), AlAs(00-1), Si(001), and one atomic layer As-covered Si(001) substrates as a function of cluster size and cluster shape by the Monte Carlo technique. Pyramidal type ledges on the GaAs clusters are found to be the favored ledge for the first three layers while an inverted-pyramidal type ledge is also favored in certain cases for the As1/Si(001) substrate. Cluster formation at ledges is compared with cluster formation on a flat terrace for the Si(001) and the As1/Si(001) substrates.
Choi, D. K.↗