Single-crystalline nanowires of Ag(2)Se can be synthesized by templating against nanowires of trigonal Se.
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Journal Article↗
Biomedical subjects
Y Yin
Publications and source records attributed to Y Yin.
The presence of a hydrogen bond between asparagine 485 and the pi system of FAD modulates the redox potential in the reaction catalyzed by cholesterol oxidase.
Cholesterol oxidase catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. An asparagine residue (Asn485) at the active site is believed to play an important role in catalysis. To test the precise role of Asn485, we mutated it to a leucine and carried out kinetic and crystallographic studies. Steady-state kinetic analysis revealed a 1300-fold decrease in the oxidation k(cat)/K(m) for the mutant enzyme whereas the k(cat)/K(m) for isomerization is only 60-fold slower. The primary kinetic isotope effect in the mutant-catalyzed reaction indicates that 3alpha-H transfer remains the rate-determining step. Measurement of the reduction potentials for the wild-type and N485L enzymes reveals a 76 mV decrease in the reduction potential of the FAD for the mutant enzyme relative to wild type. The crystal structure of the mutant, determined to 1.5 A resolution, reveals a repositioning of the side chain of Met122 near Leu485 to form a hydrophobic pocket. Furthermore, the movement of Met122 facilitates the binding of an additional water molecule, possibly mimicking the position of the equatorial hydroxyl group of the steroid substrate. The wild-type enzyme shows a novel N-H...pi interaction between the side chain of Asn485 and the pyrimidine ring of the cofactor. The loss of this interaction in the N485L mutant destabilizes the reduced flavin and accounts for the decreased reduction potential and rate of oxidation. Thus, the observed structural rearrangement of residues at the active site, as well as the kinetic data and thermodynamic data for the mutant, suggests that Asn485 is important for creating an electrostatic potential around the FAD cofactor enhancing the oxidation reaction.
Asparagine↗
High-resolution experimental phases for tryptophanyl-tRNA synthetase (TrpRS) complexed with tryptophanyl-5'AMP.
Native data, anomalous data at three wavelengths and an independent peak-wavelength data set for SeMet-substituted protein have been collected from cryoprotected crystals of the TrpRS-adenylate product (TAM) complex to a resolution limit of 1.7 A. Independent phase sets were developed using SHARP and improved by solvent flipping with SOLOMON using molecular envelopes derived from experimental densities for, respectively, peak-wavelength SAD data from four different crystals, MAD data and their M(S)IRAS combinations with native data. Hendrickson-Lattman phase-probability coefficients from each phase set were used in BUSTER to drive maximum-likelihood refinements of well defined parts of the previously refined room-temperature 2.9 A structure. Maximum-entropy completion followed by manual rebuilding was then used to generate a model for the missing segments, bound ligand and solvent molecules. Surprisingly, peak-wavelength SAD experiments produced the smallest phase errors relative to the refined structures. Selenomethionylated models deviate from one another by 0.25 A and from the native model by 0.38 A, but all have r.m.s. deviations of approximately 1.0 A from the 2.9 A model. Difference Fourier calculations between amplitudes from the 300 K experiment and the new amplitudes at 100 K using 1.7 A model phases show no significant structural changes arising from temperature variation or addition of cryoprotectant. The main differences between low- and high-resolution structures arise from correcting side-chain rotamers in the core of the protein as well as on the surface. These changes improve various structure-validation criteria.
Crystallization↗
Template-assisted self-assembly: a practical route to complex aggregates of monodispersed colloids with well-defined sizes, shapes, and structures.
This paper describes a strategy that combines physical templating and capillary forces to assemble monodispersed spherical colloids into uniform aggregates with well-controlled sizes, shapes, and structures. When an aqueous dispersion of colloidal particles was allowed to dewet from a solid surface that had been patterned with appropriate relief structures, the particles were trapped by the recessed regions and assembled into aggregates whose structures were determined by the geometric confinement provided by the templates. We have demonstrated the capability and feasibility of this approach by assembling polystyrene beads and silica colloids (> or =150 nm in diameter) into complex aggregates that include polygonal or polyhedral clusters, linear or zigzag chains, and circular rings. We have also been able to generate hybrid aggregates in the shape of HF or H2O molecules that are composed of polymer beads having different diameters, polymer beads labeled with different organic dyes, and a combination of polymeric and inorganic beads. These colloidal aggregates can serve as a useful model system to investigate the hydrodynamic and optical scattering properties of colloidal particles having nonspherical morphologies. They should also find use as the building blocks to generate hierarchically self-assembled systems that may exhibit interesting properties highly valuable to areas ranging from photonics to condensed matter physics.
Journal Article↗
Erythromycin biosynthesis. The 4-pro-S hydride of NADPH is utilized for ketoreduction by both module 5 and module 6 of the 6-deoxyerythronolide B synthase.
Incubation of chirally deuterated NADPH with 6-deoxyerythronolide B synthase (DEBS) modules 5 and module 6 and analysis of the derived triketide lactones established that the two ketoreductase domains, KR5 and KR6, are both specific for the 4-pro-S hydride of the nicotinamide cofactor.
Bacteria↗
Transcription factor RF2a alters expression of the rice tungro bacilliform virus promoter in transgenic tobacco plants.
The promoter from rice tungro bacilliform badnavirus (RTBV) is expressed only in phloem tissues in transgenic rice plants. RF2a, a b-Zip protein from rice, is known to bind to the Box II cis element near the TATA box of the promoter. Here, we report that the full-length RTBV promoter and a truncated fragment E of the promoter, comprising nucleotides -164 to +45, result in phloem-specific expression of beta-glucuronidase (GUS) reporter genes in transgenic tobacco plants. When a fusion gene comprising the cauliflower mosaic virus 35S promoter and RF2a cDNA was coexpressed with the GUS reporter genes, GUS activity was increased by 2-20-fold. The increase in GUS activity was positively correlated with the amount of RF2a, and the expression pattern of the RTBV promoter was altered from phloem-specific to constitutive. Constitutive expression of RF2a did not induce morphological changes in the transgenic plants. In contrast, constitutive overexpression of the b-ZIP domain of RF2a had a strong effect on the development of transgenic plants. These studies suggest that expression of the b-Zip domain can interfere with the function of homologues of RF2a that regulate development of tobacco plants.
Agrobacterium tumefaciens↗
A self-assembly approach to the formation of asymmetric dimers from monodispersed spherical colloids.
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Journal Article↗
Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent.
Dissolved organic matter (DOM) was concentrated from natural waters and the effluent of a wastewater treatment plant using a portable reverse osmosis (RO) system. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fractions were isolated and purified by the XAD-8 resin combined with the cation exchange resin method. The FA fractions predominated in natural waters and accounted for 54-68% of the total amount of dissolved organic carbon (DOC), whereas the HA and HyI fractions constituted, respectively, 13-29 and 9-30% of the total DOC. The effluent of wastewater was almost devoid of HA and the HyI fraction exceeded FA. The elemental compositions of HA and FA were in the ranges typical for natural humic materials, but the HyI fractions did not exhibit humic character. 1H NMR spectra revealed that the HyI fractions were almost devoid of aromatic protons and the aliphatic region featured more sharp signals than HA and FA fractions, indicating that HyI fractions were consisted of more simple compounds and less complex mixtures. The aliphatic functional groups in these fractions of DOM samples followed the order HA < FA HyI. The rate of Cu complexation with the HyI fraction was faster than the rate with the HA or FA fraction of the Suwannee River DOM, implying that copper reacted with relatively weak ligands faster than with strong ligands.
Benzopyrans↗
8-Cl-adenosine mediated cytotoxicity and sensitization of T-lymphoblastic leukemia cells to TNFalpha-induced apoptosis is via inactivation of NF-kappaB.
These data show that 8-Cl-cAMP is cytotoxic to the lymphoblastic leukemia cell line CEM and its vinblastine selected multidrug resistant derivative, CEM/VLB100 although PKA was not involved in these effects. The cytotoxic effects of 8-Cl-cAMP was abrogated by cotreatment with either ADA or IBMX which indicated a degradation form of 8-Cl-cAMP was needed for this cytotoxicity. CEM and CEM/VLB100 cells displayed a notable sensitivity to 8-Cl-adenosine-induced growth inhibition and apoptosis. 8-Cl-adenosine increased the cytosolic levels of IkappaBalpha which prevented NF-kappaB nuclear translocation. 8-Cl-adenosine also prevented TNFalpha-induced IkB decay and NF-kappaB activation in CEM and CEM/VLB100 cells.
2-Chloroadenosine↗
Distribution of distinct vacA, cagA and iceA alleles in Helicobacter pylori in Hong Kong.
BACKGROUND: There is a substantial genetic heterogeneity among Helicobacter pylori strains, and certain genotypes have been suggested to be associated with the virulence of this pathogen. The aim of this study was to investigate the distribution of H. pylori vacA, cagA and iceA genotypes and their association with duodenal ulcer disease in Hong Kong. MATERIALS AND METHODS: Gastric biopsies of 72 H. pylori infected patients were analyzed by specific polymerase chain reactions. RESULTS: Of the 72 cases, 69 (95.8%) had vacA signal sequence s1c strains, and three (4.2%) had s1a strains. vacA middle region sequences, m1b and m2, were detected in 23 (31.9%) and 46 (63.9%), respectively. Six (8.3%) cases contained multiple vacA subtypes. vacA s2 allele was only observed in three (4.3%) cases, which were also infected with s1c subtype. cagA was present in 64 (88.9%) of 72 patients, and iceA1 subtype was detected in 46 (63.9%) cases. Neither cagA nor vacA and iceA were associated with duodenal ulcer disease. CONCLUSION: The distribution of vacA, cagA and iceA alleles in H. pylori strains in Hong Kong is similar to that in east Asia. There is a difference in the distribution of genotypes between strains in Hong Kong and those in mainland China, although strains in the two regions exhibit a very close relation. The association of these virulence genes and duodenal ulcer disease needs reappraisal, particularly under geographic considerations.
Adolescent↗
Wrist fractures: what the clinician wants to know.
With the recent improvements in diagnosis and treatment of distal radius and carpal injuries, the hand surgeons' expectations of relevant radiologic interpretation of imaging studies are heightened. Conventional radiographic examinations, as well as more sophisticated and invasive studies, have important roles in the evaluation of wrist fractures and dislocations. On the basis of physical examination results and the mechanism of injury, the onus is on the examining surgeon to pinpoint potential sites of bone or ligament disruption. After this evaluation, appropriate imaging studies appropriately performed and interpreted will help direct treatment and improve outcome with greater clarity and certainty.
Carpal Bones↗
Glomerular laminin isoform transitions: errors in metanephric culture are corrected by grafting.
Glomerular basement membrane (GBM) assembly and maturation are marked by the replacement of laminin-1 (containing alpha 1-, beta 1-, and gamma 1-chains) with laminin-11 (consisting of alpha 5-, beta 2-, and gamma 1-chains). Similarly, the alpha 1- and alpha 2-chains of type IV collagen are replaced by collagen alpha 3-, alpha 4-, and alpha 5(IV)-chains. The cellular origins of these molecules and mechanisms for isoform removal and substitution are unknown. To explore glomerular laminin isoform transitions in vitro, we assessed metanephric organ cultures. Standard culture conditions do not support endothelial cell differentiation, and glomerular structures that form in vitro are avascular. Nevertheless, extensive podocyte development occurs in these cultures, including the formation of foot processes and assembly of a GBM-like matrix. Here, we show that the podocyte-specific markers, glomerular epithelial protein 1 and nephrin, which are normally expressed in capillary loop stage glomeruli in vivo, are also expressed by glomerular figures that form in organ culture. However, the GBM-like segments that form in vitro do not undergo normal laminin isoform switching. Instead, both laminin alpha 1- and alpha 5-chains are present, as is the beta 1-chain, but not beta 2. When avascular organ-cultured kidneys are grafted into anterior eye chambers, however, kidney-derived angioblasts establish extensive vasculature by 6 days, and glomeruli are lined by endothelial cells. We evaluated embryonic day 12 (E12) vascular endothelial growth factor receptor (Flk1)-lacZ kidneys that had first been grown in organ culture for 6--7 days and then grafted into wild-type mice. Correct laminin isoform substitution occurred and correlated with the appearance of endothelial cells expressing Flk1. Our findings indicate that endothelial cells, and/or factors present in the circulation, mediate normal GBM laminin isoform transitions in vivo.
Amino Acid Sequence↗
[Overexpression of heat shock protein 70 and spontaneous cancer cell apoptosis in hepatocellular carcinoma].
OBJECTIVE: To evaluate the expression of heat shock protein 70 (HSP70) and its relation to spontaneous cancer cell apoptosis in hepatocellular carcinoma (HCC). METHODS: A series of 68 resected HCC tissues from untreated patients and 68 adjacent normal liver tissues were analyzed for HSP70 expression and apoptosis by immunohistochemical SP and TUNEL methods. RESULTS: HSP70 was detected positive in 48/68(71%) cases of HCC and 19/68(28%) cases of the adjacent liver tissues. Overexpression of HSP70 was found in 36/68(53%) cases of HCC and 14/68(21%) cases of the liver tissues. The positive rate and overexpression of HSP70 were significantly higher in HCC than in the liver tissues (P<0.01). Apoptosis index was 8.9 in HCC and 1.9 in the liver tissues, showing significant different between the two groups (P<0.01). The positive rate of HSP70 was correlated with apoptosis index (r=0.8765, P<0.05) and both of them correlated with HCC histological grades. CONCLUSIONS: These results suggest that there is an overexpression of HSP70 and spontaneous cancer cell apoptosis in HCC. They seem to be markers of poor proliferation.
Apoptosis↗
[A study on the pathogenesis of Streptococcus mitis exotoxin].
OBJECTIVE: To study the isolation, purification and pathogenesis of Streptococcus mitis pyrogenic exotoxin causing toxic shock syndrome. METHODS: Streptococcus mitis isolated from patients' throat were shaking cultivated. After being centrifuged, the supernatant fluid of the culture was precipitated with 20%, 40%, 60%, 80% (NH(4))(2)SO(4) respectively and the fast protein liquid chromatography(FPLC) was used for the final step of purification. Rabbits receiving subcutaneous injection with respective purified proteins were monitored daily for fever. The ability of the purified proteins to enhance the susceptibility of the rabbits to lethal Escherichia coli endotoxin shock is recorded, when the endotoxin was injected intravenously 4 hours after administration of 10 microg Streptococcus mitis exotoxin. RESULTS: Only the protein precipitated by 20% (NH(4))(2)SO(4) (molecular weight is 34,000) from culture supernatant fluid was pyrogenic for rabbits (average temperature increase near 1 degrees C), and it can also cause the proliferation of rabbit splenocytes (mitogenicity). All the animals receiving subcutaneous injection of exotoxin containing purified proteins precipitated with higher concentrations of (NH(4))(2)SO(4) died within 16 approximately 29 hours after intravenous injection of the Escherichia coli endotoxin, demonstrating the enhanced susceptibility of the animals to lethal endotoxin shock. The control rabbits displayed none of these effects. CONCLUSION: Streptococcus mitis exotoxin is a novel streptococcal pyrogenic exotoxin.
Animals↗
[Analysis of the changes of temporomandibular joint under repeated +Gz stress].
Changes of temporomandibular joint (TMJ) under repeated +Gz stress were discussed. From the etiological point of view in TMJ, many papers in the fields of aviation medicine, microcirculation, maxillofacial surgery and bone surgery were reviewed. +Gz forces can cause inadequacy of blood of oxygen supply to TMJ area. This situation can be worsened by release of free radical agent and cellular factors, ischemia/reperfusion injury, and/or hemorrheologic changes. Furthermore, G-induced injury of cervical muscles and spine may break the maxillofacial muscle chain balance. In addition to the above factors, mental stress may do harm to TMJ. This paper introduced the researches on this area in an attempt to enlighten the concern about TMJ responses to increased +Gz acceleration forces.
Aerospace Medicine↗
[Study on the Apriona germari(Hope) larvae's intestinal bacterial flora].
Intestinal flora of 47 Apriona germari(Hope) larvae, collected from fields, had been isolated and identified. The results showed that the predominant bacteria were Staphylococcus. Its viable count was 7.63 +/- 0.21, and the detection rate was 100%. Meanwhile, a strain of cellulose-utilizing bacterium was isolated from the fore-midgut fluid of A. germari larvae with the cellulose-congo red agar medium. The bacterium was tentatively identified as Cellulomonas. The detection rate of the cellulolytic bacterium was 23.40%, and the count was 3.84 +/- 0.54 approximately. Its contribution to the borer's cellulose digestion needs further investigations.
Animals↗
[The design of ECG sample device based on Windows 98/95].
The ECG sample system which is based on Microsoft Windows98/95 and IBM-compatible PCs ISA bus, is introduced here. It includes ECG sample device, virtual device driver(VxD) and application program, By the method, we can design the device simply and make good use of the computer to programming powerful auto recognition software and telediagnosis software. The system is a cheap and mini medical apparatus. Applications in family care and community medical treatment are encouraging.
Electrocardiography↗
Amiodarone has exclusively non-genomic action on cardiac beta-adrenoceptor regulation.
The antiarrhythmic drug amiodarone down-regulates the density of cardiac beta-adrenoceptors behaving as a triiodothyronine (T(3)) antagonist. It is still unclear if amiodarone acts at the nuclear (genomic) and/or the non-genomic levels. Using Northern blot analysis, we showed that the amiodarone had no effect on the increase of beta(1)-adrenoceptor mRNA level induced by the T(3)-administration in the heart of thyroidectomised rats. Thus, our results suggest that amiodarone has no genomic effect. Consequently, we investigated whether amiodarone down-regulation of beta-adrenoceptor number in T(3)-stimulated cardiomyocytes could be explained by changes in the rate of cell surface receptor protein turnover. Indeed, the binding studies of cyclohexidemide-treated cells showed that amiodarone suppressed the T(3)-induced decrease in the rate of the cell surface receptor disappearance. In conclusion, our findings indicate that the modulation of cardiac beta-adrenoceptor density by amiodarone involves only non-genomic targets required in T(3)-dependent regulation of the cell surface beta-adrenoceptor turnover.
Amiodarone↗