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Search Results: 1 - 10 of 3102 matches for " Kwan-Kit Woo "
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Production of Cyclodextrin Glycosyltransferase (CGTase) by Bacillus lehensis S8 using Sago Starch as Carbon Source
Pui-Woon Yap,Arbakariya B. Ariff,Kwan-Kit Woo,Siew-Ling Hii
Journal of Biological Sciences , 2010,
Abstract: Production of cyclodextrin glycosyltransferase (CGTase) is influenced by the reaction of the CGTase-producing strain towards various types of substrates. Variations in environmental factors such as concentrations of carbon and nitrogen sources possess significant effects on CGTase production. The present study was conducted with the prime purpose to optimise the cultivation medium in enhancing the CGTase production by a locally isolated alkalophilic Bacillus sp. The CGTase fermentation processes were performed in 250 mL Erlenmeyer flasks containing 200 mL of production medium with continuous shaking at 200 rpm and 37°C. Optimisation process was conducted by using change-a-factor-at-a-time method. From the study, an indigenous Malaysian carbon source, i.e., sago starch was found capable in improving the CGTase production with the CGTase yield of 18452 U g-1 at 0.1% w/v of starch. In addition to that, by using yeast extract as the sole nitrogen source in the medium, the CGTase excretion by the isolate is greatly enhanced as compared to the basal medium which employed two types of nitrogenous compounds. The optimised growth medium that has been successfully developed for high level of CGTase production by using the locally isolated Bacillus lehensis in 250 mL Erlenmeyer flask is comprised of (% w/v): 0.1% sago starch, 1% yeast extract, 1% sodium carbonate, 0.009% magnesium sulphate and 0.1% di-potassium hydrogen phosphate.
Born Effective Charges and Infrared Response of LiBC
Kwan-Woo Lee,W. E. Pickett
Physics , 2003, DOI: 10.1103/PhysRevB.68.085308
Abstract: Calculations of the zone center optical mode frequencies (including LO-TO splitting), Born effective charges Z$^*_{\alpha\alpha}$ for each atom, dielectric constants $\epsilon_{0}$ and $\epsilon_{\infty}$, and the dielectric response in the infrared, using density functional linear response theory, are reported. Calculated Raman modes are in excellent agreement with experimental values (170 cm$^{-1}$ and 1170 cm$^{-1}$), while it will require better experimental data to clarify the infrared active mode frequencies. The Born effective charges Z$^*_{\alpha \alpha}$ (i) have surprisingly different values for B and C, and (ii) show considerable anisotropy. Relationships between the effective charges and LO-TO splitting are discussed, and the predicted reflectivity in the range 0 -- 1400 cm$^{-1}$ is presented. These results hold possible implications for Li removal in LiBC, and C substition for B in MgB$_2$.
Organometallic-like localization of 4d-derived spins in an inorganic conducting niobium suboxide
Kwan-Woo Lee,Warren E. Pickett
Physics , 2015, DOI: 10.1103/PhysRevB.91.195152
Abstract: Based on the refined crystal structure comprised of columns of 3*4 planar blocks of NbO6 octahedra and first principles electronic structure methods, we find that orthorhombic (o)-Nb$_{12}$O$_{29}$ introduces a new class of transition metal oxide. The electronic system consists of a large Nb dimer-based localized orbital comparable in size to those in organometallic compounds, yet is tightly bound and weakly interacting with itinerant electronic bands. These local moments, a rare occurrence for Nb, form one-dimensional spin chains that criss-cross perpendicularly oriented conducting nanowires. The local moment bandwidth is comparable to what is seen in rare earth compounds with extremely localized orbitals. The microscopic origin is traced to the local structure of the NbO6 octahedra and associated orbital+spin ordering. The resulting 1D$_s$*1D$_c$ anisotropic two dimensional Heisenberg-Kondo lattice model (s=spin, c=charge) provides a strongly anisotropic spin-fermion lattice system for further study.
Hypertensive-Nimodipine Therapy for Middle Cerebral Artery Vasospasm after Resection of Glioblastoma Multiforme: A Case Report and Literature Review  [PDF]
Peter Yat Ming Woo, Ka Wing Michael See, Jason Kwan Ho Chow, Yung Chan, Hoi Tung Wong, Kwong Yau Chan
Open Journal of Modern Neurosurgery (OJMN) , 2015, DOI: 10.4236/ojmn.2015.53013
Abstract: Delayed cerebral ischemia (DCI) due to post-brain tumor resection vasospasm is an often unrecognized yet debilitating complication. We present a patient with DCI after the resection of glioblastoma multiforme (GBM). To our knowledge, this is the first report on DCI after GBM resection. A 52-year-old female patient with headache for one month underwent subtotal resection of a left temporal GBM encasing the proximal middle cerebral artery (MCA). She was well during the immediate postoperative period but developed right upper limb dense monoparesis on postoperative day four with computed tomographic angiography confirming left MCA vasospasm. Symptoms were significantly alleviated with weeklong hypertensive therapy and nimodipine administration; however they recurred soon after cessation of treatment. A high index of clinical suspicion is needed for the diagnosis of post-tumor resection DCI. Any new postoperative neurological deficit that cannot be explained by hemorrhage, seizures or infection should be expeditiously investigated by angiography or transcranial Doppler sonography. Prompt initiation of hypertensive and nimodipine therapy can possibly reverse neurological deficit. Treatment should be guided by Doppler, angiographic or perfusion imaging studies and not by clinical improvement alone.
Doping-dependent bandwidth renormalization and spin-orbit coupling in (Sr$_{1-x}$La$_x$)$_2$RhO$_4$
Kyo-Hoon Ahn,Kwan-Woo Lee,Jan Kunes
Physics , 2014, DOI: 10.1088/0953-8984/27/8/085602
Abstract: We investigate the electronic structure of (Sr$_{1-x}$La$_x$)$_2$RhO$_4$ using a combination of the density functional and dynamical mean-field theories. Unlike the earlier local density approximation plus Hubbard $U$ (LDA+U) studies, we find no sizable enhancement of the spin-orbit splitting due to electronic correlations and show that such an enhancement is a spurious effect of the static mean-field approximation of the LDA+U method. The electron doping suppresses the importance of electronic correlations, which is reflected in quasi-particle bandwidth increasing with $x$. (Sr$_{1-x}$La$_x$)$_2$RhO$_4$ can be classified as weakly correlated metal, which becomes an itinerant in-plane ferromagnet (but possibly A-type antiferromagnet) due to Stoner instability around $x=0.2$.
High-Density Transcriptional Initiation Signals Underline Genomic Islands in Bacteria
Qianli Huang, Xuanjin Cheng, Man Kit Cheung, Sergey S. Kiselev, Olga N. Ozoline, Hoi Shan Kwan
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033759
Abstract: Genomic islands (GIs), frequently associated with the pathogenicity of bacteria and having a substantial influence on bacterial evolution, are groups of “alien” elements which probably undergo special temporal–spatial regulation in the host genome. Are there particular hallmark transcriptional signals for these “exotic” regions? We here explore the potential transcriptional signals that underline the GIs beyond the conventional views on basic sequence composition, such as codon usage and GC property bias. It showed that there is a significant enrichment of the transcription start positions (TSPs) in the GI regions compared to the whole genome of Salmonella enterica and Escherichia coli. There was up to a four-fold increase for the 70% GIs, implying high-density TSPs profile can potentially differentiate the GI regions. Based on this feature, we developed a new sliding window method GIST, Genomic-island Identification by Signals of Transcription, to identify these regions. Subsequently, we compared the known GI-associated features of the GIs detected by GIST and by the existing method Islandviewer to those of the whole genome. Our method demonstrates high sensitivity in detecting GIs harboring genes with biased GI-like function, preferred subcellular localization, skewed GC property, shorter gene length and biased “non-optimal” codon usage. The special transcriptional signals discovered here may contribute to the coordinate expression regulation of foreign genes. Finally, by using GIST, we detected many interesting GIs in the 2011 German E. coli O104:H4 outbreak strain TY-2482, including the microcin H47 system and gene cluster ycgXEFZ-ymgABC that activates the production of biofilm matrix. The aforesaid findings highlight the power of GIST to predict GIs with distinct intrinsic features to the genome. The heterogeneity of cumulative TSPs profiles may not only be a better identity for “alien” regions, but also provide hints to the special evolutionary course and transcriptional regulation of GI regions.
2011 German Escherichia coli O104:H4 outbreak: whole-genome phylogeny without alignment
Man-Kit Cheung, Lei Li, Wenyan Nong, Hoi-Shan Kwan
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-533
Abstract: We reconstructed the phylogeny of E. coli using the genome-wide and alignment-free feature frequency profile method and revealed the 2001 strain to be the closest relative to the 2011 outbreak strain among all available E. coli strains at present and confirmed findings from previous alignment-based phylogenetic studies that the HUS-causing O104:H4 strains are more closely related to typical enteroaggregative E. coli (EAEC) than to enterohemorrhagic E. coli. Detailed re-examination of pathogenicity-related virulence factors and secreted proteins showed that the 2001 strain possesses virulence factors shared between typical EAEC and the 2011 outbreak strain.Our study represents the first attempt to elucidate the whole-genome phylogeny of the 2011 German outbreak using an alignment-free method, and suggested a direct line of ancestry leading from a putative EAEC-like ancestor through the 2001 strain to the 2011 outbreak strain.In early May 2011, a large outbreak of diarrhea with associated hemolytic-uremic syndrome (HUS) began in Germany. Until its official end in late July, 782 cases of HUS (29 deaths) and 3128 non-HUS cases (17 deaths) were reported, making it the largest outbreak of HUS worldwide [1]. Diarrhea associated with HUS is usually caused by enterohemorrhagic E. coli (EHEC) [2]. However, the outbreak strain was serotyped to be O104:H4, which historically caused very few HUS cases [3]. Early PCR assay and cell-adherence assay revealed genotypic and phenotypic characteristics of enteroaggregative E. coli (EAEC) [4]. In order to characterize the unusual strain, genomes of ten outbreak isolates were sequenced using next-generation and third-generation sequencing technologies [5-8]. The genome sequence of a historical O104:H4 strain, 01-09591, isolated in 2001 [9] was also obtained [8].Phylogenetic analyses were performed to understand the evolution of the outbreak strain using various approaches [5,6,8,10]. However, the multilocus sequence analysis (MLSA)-based
Efficient Complex Continuous-Time IIR Filter Design via Generalized Vector Fitting
Chi-Un Lei,Chung-Man Cheung,Hing-Kit Kwan,Ngai Wong
Lecture Notes in Engineering and Computer Science , 2008,
A Novel Lentinula edodes Laccase and Its Comparative Enzymology Suggest Guaiacol-Based Laccase Engineering for Bioremediation
Kin-Sing Wong, Man-Kit Cheung, Chun-Hang Au, Hoi-Shan Kwan
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0066426
Abstract: Laccases are versatile biocatalysts for the bioremediation of various xenobiotics, including dyes and polyaromatic hydrocarbons. However, current sources of new enzymes, simple heterologous expression hosts and enzymatic information (such as the appropriateness of common screening substrates on laccase engineering) remain scarce to support efficient engineering of laccase for better “green” applications. To address the issue, this study began with cloning the laccase family of Lentinula edodes. Three laccases perfectio sensu stricto (Lcc4A, Lcc5, and Lcc7) were then expressed from Pichia pastoris, characterized and compared with the previously reported Lcc1A and Lcc1B in terms of kinetics, stability, and degradation of dyes and polyaromatic hydrocarbons. Lcc7 represented a novel laccase, and it exhibited both the highest catalytic efficiency (assayed with 2,2′-azino-bis(3-ethylbenzothiazoline-6-?sulfonicacid) [ABTS]) and thermostability. However, its performance on “green” applications surprisingly did not match the activity on the common screening substrates, namely, ABTS and 2,6-dimethoxyphenol. On the other hand, correlation analyses revealed that guaiacol is much better associated with the decolorization of multiple structurally different dyes than are the two common screening substrates. Comparison of the oxidation chemistry of guaiacol and phenolic dyes, such as azo dyes, further showed that they both involve generation of phenoxyl radicals in laccase-catalyzed oxidation. In summary, this study concluded a robust expression platform of L. edodes laccases, novel laccases, and an indicative screening substrate, guaiacol, which are all essential fundamentals for appropriately driving the engineering of laccases towards more efficient “green” applications.
Methylation of miR-34a, miR-34b/c, miR-124-1 and miR-203 in Ph-negative myeloproliferative neoplasms
Chor Sang Chim, Thomas S Wan, Kwan Yeung Wong, Tsz Kin Fung, Hans G Drexler, Kit Fai Wong
Journal of Translational Medicine , 2011, DOI: 10.1186/1479-5876-9-197
Abstract: We studied DNA methylation of these miRs in Philadelphia-negative (Ph-ve) myeloproliferative neoplasms (MPNs). Methylation-specific PCR (MSP), verified by direct sequencing of the methylated MSP products, was performed in cell lines, normal controls and diagnostic marrow samples of patients with MPNs.Methylation of these miRs was absent in the normal controls. miR-34b/c were homozygously methylated in HEL cells but heterozygously in MEG-01. In HEL cells, homozygous miR-34b/c methylation was associated with miR silencing, and 5-aza-2'-deoxycytidine treatment led to re-expression of both miR-34b and miR-34c, consistent with that both miRs are under the regulation of the same promoter CpG island. miR-34a was heterozygously methylated in MEG-01 and K-562. miR-203 was completely unmethylated in K-562 and SET-2 but no MSP amplification was found in both HEL and MEG-01, suggestive of miR deletion. In primary samples, four each had miR-34b/c and -203 methylation, in which two had concomitant methylation of miR-34b/c and -203. miR-34a was methylated in one patient and none had methylation of miR-124-1. Seven patients (15.6%) had methylation of at least one of the four miRs. miR methylation did not correlate with clinical parameters, disease complications or JAK2 V617F mutation.This is the first report of miR hypermethylation in MPNs. miR-203 hypermethylation is not specific to Ph+ve leukemias but also present in Ph-ve MPNs. miR-34b/c methylation was associated with reversible miR silencing. There was no correlation of miR methylation with clinical demographic data or outcome.Philadelphia-negative (Ph-ve) myeloproliferative neoplasm (MPN) is a stem cell disease with proliferation of myeloid lineage, leading to the development of distinct clinical entities including polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) [1-3]. JAK2 V617F mutation, resulting in constitutive activation of JAK-STAT signaling, occurs in about half of the patients wi
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