Expression, purification and initial characterization of Halobacterium proline dehydrogenase

Abstract only availableNature recycles proline by converting it to glutamate. This 4-electron oxidation process is catalyzed by two catabolic enzymes, proline dehydrogenase (PRODH) and Δ1-pyrroline-5-carboxylate dehydrogenase (P5CDH). Inborn defects in PRODH and P5CDH result in the disorders hyperprolinemia I & II, respectively. These conditions are often associated with mental retardation, convulsions, and brain disorders. PRODH has also been implicated in schizophrenia susceptibility, cancer and P53-mediated apoptosis. Despite their importance in human health and disease, these enzymes have not been extensively studied. Thus, the goal of this research is to characterize the structure and function of PRODH. The work presented here focuses on a newly discovered homologue of PRODH found in archaea, which we identified by bioinformatics analysis of genome sequence data. Archaea are also genetically more closely related to eukaryotes than bacteria, so study of their proteins may provide insights into homologous eukaryotic enzymes. Archaea are some of the Earth's oldest life forms and are known for living in extreme environments. The PRODH researched here is from the Halobacterium (salt-loving), which can be found in places such as the Dead Sea and the Great Salt Lake. Preliminary results so far include testing the expression of Halobacterium PRODH, known as YusM, in two different E. coli expression systems, BL21(DE3)pLysS and Rosetta2. The latter strain was used to account for rare codon usage by Halobacterium. Parameters varied in these expression tests included time and temperature of induction as well as IPTG concentration. After expression, the cells were broken in a French pressure cell and the cell debris was pelleted with centrifugation. YusM was found to be largely associated with the cell pellet; therefore protein purification under denaturing conditions was investigated. The use of urea as a denaturing reagent has been successful for purifying YusM. Once the protein was renatured it showed improved kinetic activity. We believe the improved activity is due to disruption of improperly folded protein by the denaturant, followed by re-folding into the native, or near-native, state. Further studies will need to be done to determine the cause of misfolding in the E. coli cell.Stevens' Chemistry Progra

Optimal Routes to Ultrafast Polarization Reversal in Ferroelectric LiNbO3

We use the frozen phonon method to calculate the anharmonic potential energy surface and to model the ultrafast ferroelectric polarization reversal in LiNbO3 driven by intense pulses of THz light. Before stable switching of the polarization occurs, there exists a region of excitation field-strengths where transient switching can occur, as observed experimentally [Physical Review Letters 118, 197601 (2017)]. By varying the excitation frequency from 4 to 20 THz, our modeling suggests that more efficient, permanent polarization switching can occur by directly exciting the soft mode at 7 THz, compared to nonlinear phononic-induced switching driven by exciting a high frequency mode at 18 THz. We also show that neglecting anharmonic coupling pathways in the modeled experiment can lead to significant differences in the modeled switching field strengths.Comment: 8 pages, 3 figure

Fast path and polarisation manipulation of telecom wavelength single photons in lithium niobate waveguide devices

We demonstrate fast polarisation and path control of photons at 1550 nm in lithium niobate waveguide devices using the electro-optic effect. We show heralded single photon state engineering, quantum interference, fast state preparation of two entangled photons and feedback control of quantum interference. These results point the way to a single platform that will enable the integration of nonlinear single photon sources and fast reconfigurable circuits for future photonic quantum information science and technology.Comment: 6 page

Engineering xylose metabolism in Thraustochytrid T18

Thraustochytrids spp are oleaginous marine protists with significant potential for biofuel production at industrial levels; however, the cost of feedstocks has been a major challenge in making this process economical. On a quest for cheaper and renewable feedstocks, we investigated the ability of Thraustochytrid strain T18 to grow in the presence of xylose and demonstrated its ability to produce xylitol. However, genome sequencing and in vivo enzymatic assays revealed the presence of a xylose isomerase which indicates there are two xylose metabolism pathways in Thraustochytrid T18: a xylose reductase/xylitol dehydrogenase pathway as well as an isomerase pathway. Characterization of the two native pathways suggested that xylitol production is a bottleneck to T18 xylose metabolism. Through various strain improvement strategies, including over-expression of the endogenous xylose isomerase and heterologous xylulose kinases, we enhanced xylose usage while reducing xylitol production by \u3e50% and 80%, respectively, compared to wild-type. Highest levels of xylose metabolism were obtained through selection of strains possessing multiple copies of the transgenes. The xylose usage of the best xylose metabolizing isolate was further validated through fermentation. These newly engineered strains pave the way to using T18 for biofuel production using hemicellulosic feedstock

Photon Pair Generation in Silicon Micro-Ring Resonator with Reverse Bias Enhancement

Photon sources are fundamental components for any quantum photonic technology. The ability to generate high count-rate and low-noise correlated photon pairs via spontaneous parametric down-conversion using bulk crystals has been the cornerstone of modern quantum optics. However, future practical quantum technologies will require a scalable integration approach, and waveguide-based photon sources with high-count rate and low-noise characteristics will be an essential part of chip-based quantum technologies. Here, we demonstrate photon pair generation through spontaneous four-wave mixing in a silicon micro-ring resonator, reporting a maximum coincidence-to-accidental (CAR) ratio of 602 (+-) 37, and a maximum photon pair generation rate of 123 MHz (+-) 11 KHz. To overcome free-carrier related performance degradations we have investigated reverse biased p-i-n structures, demonstrating an improvement in the pair generation rate by a factor of up to 2, with negligible impact on CAR.Comment: 5 pages, 3 figure

Gallium Arsenide (GaAs) Quantum Photonic Waveguide Circuits

Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9 +/- 1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6 +/- 1.3% and 84.4 +/- 1.5% respectively were demonstrated in Mach-Zehnder interferometers exploiting the electro-optic Pockels effect. This work paves the way for a fully integrated quantum technology platform based on the GaAs material system.Comment: 10 pages, 4 figure

Questions on “world art history”

The choice of this theme for debate has been stimulated by recent discussions of the globalization of art history, and the increasing emphasis placed in the discipline on the notion of “world art history,” perhaps best exemplified by the books of James Elkins and David Summers: James Elkins, Is Art History Global? and David Summers, Real Spaces: World Art History and the Rise of Western Modernism.  Most of the discussion has focused on Renaissance and later art, but the purpose of this debate..