Biomedical subjects

Gang Yu

Publications and source records attributed to Gang Yu.

At least 55 records · Page 3Linked to original sources

PubMed2004

[Study on the degradation of polymer light-emitting diodes by in-situ micro-Raman spectroscopy].

The authors report Raman degradation study of polymer light-emitting devices under ambient conditions. In order to investigate the chemical degradation reaction in polymer light-emitting diode (PLEDs) devices, the chemical structure of the poly (2-(4-Ethylhexyl) phenyl-1, 4-phenylene vinylene) (P-PPV) polymer was analyzed by micro-Raman spectroscopy during the lifetime of the devices. The evidence for the reduction of conjugation length is provided by Raman spectroscopy. This reduction of theconjugation length, which dramatically increases the resistance and cuts off the current density, was the main reason for the failure of lighting. These findings provide an important insight into the intrinsic degradation mechanisms of the polymer LEDs and help in the development of even more stable devices.

Electrochemistry↗

PubMed2004

[Adopting the method of principal components analysis combined with correlation coefficient to increase the predicted concentration's accuracy of benzene and its homology mixture].

The concentrations of benzene and its homology mixture were measured by near infrared spectra, and the emphasis was put on the character of the principal component and its physical significance. It is pointed out that the anterior principal components are very similar to the correlation coefficient of the multi-component solution and the theoretical proof for the right condition is given. The high frequency noise of the system can be checked out by principal component combined with the correlation coefficient. Removing the noise can greatly increase the accuracy of the prediction model.

Benzene↗

PubMed2003

A conserved GXXXG motif in APH-1 is critical for assembly and activity of the gamma-secretase complex.

The multipass membrane protein APH-1, found in the gamma-secretase complex together with presenilin, nicastrin, and PEN-2, is essential for Notch signaling in Caenorhabditis elegans embryos and is required for intramembrane proteolysis of Notch and beta-amyloid precursor protein in mammalian and Drosophila cells. In C. elegans, a mutation of the conserved transmembrane Gly123 in APH-1 (mutant or28) leads to a notch/glp-1 loss-of-function phenotype. In this study, we show that the corresponding mutation in mammalian APH-1aL (G122D) disrupts the physical interaction of APH-1aL with hypoglycosylated immature nicastrin and the presenilin holoprotein as well as with mature nicastrin, presenilin, and PEN-2. The G122D mutation also reduced gamma-secretase activity in intramembrane proteolysis of membrane-tethered Notch. Moreover, we found that the conserved transmembrane Gly122, Gly126, and Gly130 in the fourth transmembrane region of mammalian APH-1aL are part of the membrane helix-helix interaction GXXXG motif and are essential for the stable association of APH-1aL with presenilin, nicastrin, and PEN-2. These findings suggest that APH-1 plays a GXXXG-dependent scaffolding role in both the initial assembly and subsequent maturation and maintenance of the active gamma-secretase complex.

Amino Acid Motifs↗

PubMed2003

PEN-2 and APH-1 coordinately regulate proteolytic processing of presenilin 1.

Presenilin (PS, PS1/PS2) complexes are known to be responsible for the intramembranous gamma-secretase cleavage of the beta-amyloid precursor protein and signaling receptor Notch. PS holoprotein undergoes endoproteolysis by an unknown enzymatic activity to generate NH(2)- and COOH-terminal fragments, a process that is required for the formation of the active and stable PS/-gamma-secretase complex. Biochemical and genetic studies have recently identified nicastrin, APH-1, and PEN-2 as essential cofactors that physically interact with PS1 and are necessary for the gamma-secretase activity. However, their precise function in regulating the PS complex and gamma-secretase activity remains unknown. Here, we demonstrate that endogenous PEN-2 preferentially interacts with PS1 holoprotein. Down-regulation of PEN-2 expression by small interfering RNA (siRNA) abolishes the endoproteolysis of PS1, whereas overexpression of PEN-2 promotes the production of PS1 fragments, indicating a critical role for PEN-2 in PS1 endoproteolysis. Interestingly, accumulation of full-length PS1 resulting from down-regulation of PEN-2 is alleviated by additional siRNA down-regulation of APH-1. Furthermore, overexpression of APH-1 facilitates PEN-2-mediated PS1 proteolysis, resulting in a significant increase in PS1 fragments. Our data reveal a direct role of PEN-2 in proteolytic cleavage of PS1 and a regulatory function of APH-1, in coordination with PEN-2, in the biogenesis of the PS1 complex.

Amyloid Precursor Protein Secretases↗

PubMed2003

Occurrence of dissolved PAHs in the Jinsha River (Panzhihua)--upper reaches of the Yangtze River, Southwest China.

16 priority polycyclic aromatic hydrocarbons (PAHs) were determined in water samples from the Jinsha River (Panzhihua part), Southwest China. Total dissolved PAH concentrations varied from 21.89 microg l(-1) to 382.8 microg l(-1). It was found that the concentration of PAHs decreased along the flow direction due to the higher density distribution of coal chemical industry in the upstream of our study rivers. The pollution levels in our study area are significantly higher than previously reported values in other waters both in China and other countries. The predominance of benzo[k]fluoranthene and indeno[1,2,3-cd]pyrene was clearly observed in all water samples. On average these two compounds accounted for 98.3% of the total dissolved PAH concentration in water. The results showed the positive correlations among total dissolved PAHs, benzo[k]fluoranthene and indeno[1,2,3-cd]pyrene, which suggested that these two predominant PAHs have similar source and environmental behaviors in our study area. When compared with the survey results of organic micropollutants two decades ago, it was found that hydrocarbon pollution both predominated and even increased with the development of coal chemical industry in this area during the past 20 years. The results therefore provide important information on the current contamination status of a key industrial city in China, and points to the need for urgent action to investigate the relationship between the PAH composition and concentration in water from the Jinsha River and the wastewater discharge from coal chemical industry, and to identify the source, transport pathway and fate of PAHs in the area. It should then be necessary to adopt appropriate and instant measures to control the pollution around this area.

Chemical Industry↗

PubMed2003

[Contents of organochlorine pesticides in water, pore water and sediment in Minjiang River Estuary of China].

The concentrations of 18 organochlorine pesticides in water, pore water and surface sediment from Minjiang River Estuary were analyzed by GC-ECD, and confirmed by GC-MSD. The range of organochlorine pesticides was 0.532-1.82 micrograms/L at water, 4.54-13.7 micrograms/L at pore water, and 28.79-52.07 micrograms/kg at sediment. Compared with the results of other estuaries and gulfs (Pearl River Estuary, Jiulong River Estuary and so on), it showed that the pollution of organochlorines in Minjiang was some moderate. The concentration difference in surface water, middle water, bottom water, pore water and sediment, due to the higher affinity of these hydrophobic compound for sedimentary phase than to water and a potential flux of pollutants from sediment to overlying water. The predominance of beta-HCH, DDE, Heptachlor, Endosulfan II and Methoxychlor in all water, pore water and sediment were clearly observed. On average, DDE, beta-HCH, Endosulfan II occupied the most part of total DDTs, HCHs and Endosulfans respectively, indicated the fate of these parent compounds or congeners. At the same time, it was found that the positive relationship among the individual organochlorine components (HCHs, DDTs and Endosulfans), which indicated that the similar of the source and behavior for organochlorine pesticides.

China↗

PubMed2003

[Susac syndrome: a report of two cases].

OBJECTIVE: To investigate the clinic characters and diagnosis of Susac syndrome. METHODS: Two cases were systematically studied by the authors. RESULTS: All the two cases were young women. The clinical manifestations include acute and subacute multifocal and diffuse encephalopathic symptoms, hearing loss, and visual loss. Diagnosis is facilitated by demonstration of retinal arteriolar occlusions without uveitis or keratoconjunctivitis, mid-to-low frequency unilateral or bilateral sensorineural hearing loss, and numerous small foci of increased signal in the white and gray matter on T2-weighted brain magnetic resonance imaging. CONCLUSIONS: This rare syndrome often can be identified at an early stage with a careful history and physical examination. MRI, SPECT, retinal fluorescein angiography and audiometry will contribute to diagnosis.

Adult↗

PubMed2003

Influence of nonionic surfactant on the solubilization and biodegradation of phenanthrene.

Phenanthrene was solubilized in two different nonionic surfactants, Tween80 and Triton X-100. The bioavailability of phenanthrene to the bacteria isolated from the petroleum contaminated soils was studied based on the rotary flasks experiments. The results showed that the concentration of nonionic surfactants above the critical micelle concentration (CMC) can increase the solubility of phenanthrene in water and were innoxious to the phenanthrene-degrading bacteria; phenanthrene solubilized in the micelles of Tween80 was bioavailable and biodegradable. The research demonstrated the potential of surfactant-enhanced bioremediation of soils contaminated by hydrophobic organic compounds (HOCs).

Bacteria↗

PubMed2003

[Photocatalytic degradation of low level toluene in the gas phase].

Photocatalytic degradation of low level toluene in the gas phase at low retention time (17s-83s) was studied. The effects of the inlet concentration, retention time, relative humidity, ultraviolet wavelength and carrier of the catalyst were investigated, as well as the change of the photocatalytic degradation capability with the load. It was showed that the degradation rate of toluene at low retention time decreased with increase of inlet concentration, and it decreased more significantly at shorter retention time. Within a range of retention time, the degradation of toluene followed with first order kinetics approximately, and the reaction rate constant increased with inlet concentration. The relative humidity affected the degradation rate a little when the inlet concentration was low. The photocatalytic degradation rate when irradiated with low-pressure mercury lamp (254 nm) was significantly higher than that irradiated with black light lamp having same power. The photocatalyst coated on the stainless steel mesh showed higher activity while it was on the mesh with higher number, however it was not as good as the photocatalyst coated on the aluminum plate.

Air Pollutants↗

PubMed2003

[Characterization of polycyclic aromatic hydrocarbons dissolved in nonionic surfactants].

Using three typical nonionic surfactants (Tween80, Tween20 and Triton X-100), the solubilization of four kinds of polycyclic aromatic hydrocarbons (PAHs) e.g. naphthalene, phenanthrene, fluorene and pyrene, were characterized. It was found that not only nonionic surfactants could enhance the solubilization of PAHs greatly in the range of concentration above critical micellar concentration (CMC), but also the solubility had the linear relationship with the concentration of nonionic surfactants. The effect of solubilization enhancement at three surfactants was Triton X-100 > Tween80 > Tween20. In the three nonionic surfactants solution the micelle-aqueous phase partitioning coefficient (K(m)) had very good linear proportional to the octanol-water partitioning coefficient (Kow) for the four tested PAHs.

Octoxynol↗

PubMed2002

Photon absorption in resonant-cavity-enhanced gaas far-infrared detectors.

Interface reflection has been demonstrated to play an important role in GaAs multilayer homojunction far-infrared (FIR) detectors. A transfer matrix method that is able to provide a true optical field distribution within an FIR detector has been employed to optimize photon absorption and structure. The dependence of photon absorption on the reflectivity and the phase shift of the bottom mirror in a resonant-cavity-enhanced GaAs FIR detector has been investigated. Weak wavelength selectivity has been observed for both resonant and off-resonant FIR, which is a unique advantage for detector application. In comparison with the experimental result, a 20.8% increase in quantum efficiency was found in an optimized FIR detector.

Journal Article↗

PubMed2002

Alleles at the Nicastrin locus modify presenilin 1- deficiency phenotype.

Presenilin 1 (PS1), presenilin 2, and nicastrin form high molecular weight complexes that are necessary for the endoproteolysis of several type 1 transmembrane proteins, including amyloid precursor protein (APP) and the Notch receptor, by apparently similar mechanisms. The cleavage of the Notch receptor at the "S3-site" releases a C-terminal cytoplasmic fragment (Notch intracellular domain) that acts as the intracellular transduction molecule for Notch activation. Missense mutations in the presenilins cause familial Alzheimer's disease by augmenting the "gamma-secretase" cleavage of APP and overproducing one of the proteolytic derivatives, the Abeta peptide. Null mutations in PS1 inhibit both gamma-secretase cleavage of APP and S3-site cleavage of the Notch receptor. Mice lacking PS1 function have defective Notch signaling and die perinatally with severe skeletal and brain deformities. We report here that a genetic modifier on mouse distal chromosome 1, coinciding with the locus containing Nicastrin, influences presenilin-mediated Notch S3-site cleavage and the resultant Notch phenotype without affecting presenilin-mediated APP gamma-site cleavage. Two missense substitutions of residues conserved among vertebrates have been identified in nicastrin. These results indicate that Notch S3-site cleavage and APP gamma-site cleavage are distinct presenilin-dependent processes and support a functional interaction between nicastrin and presenilins in vertebrates. The dissociation of Notch S3-site and APP gamma-site cleavage activities will facilitate development of gamma-secretase inhibitors for treatment of Alzheimer's disease.

Alleles↗

PubMed2002

Mammalian APH-1 interacts with presenilin and nicastrin and is required for intramembrane proteolysis of amyloid-beta precursor protein and Notch.

Presenilin and nicastrin are essential components of the gamma-secretase complex that is required for the intramembrane proteolysis of an increasing number of membrane proteins including the amyloid-beta precursor protein (APP) and Notch. By using co-immunoprecipitation and nickel affinity pull-down approaches, we now show that mammalian APH-1 (mAPH-1), a conserved multipass membrane protein, physically associates with nicastrin and the heterodimers of the presenilin amino- and carboxyl-terminal fragments in human cell lines and in rat brain. Similar to the loss of presenilin or nicastrin, the inactivation of endogenous mAPH-1 using small interfering RNAs results in the decrease of presenilin levels, accumulation of gamma-secretase substrates (APP carboxyl-terminal fragments), and reduction of gamma-secretase products (amyloid-beta peptides and the intracellular domains of APP and Notch). These data indicate that mAPH-1 is probably a functional component of the gamma-secretase complex required for the intramembrane proteolysis of APP and Notch.

Amino Acid Sequence↗

PubMed2002

Mature glycosylation and trafficking of nicastrin modulate its binding to presenilins.

Nicastrin is an integral component of the high molecular weight presenilin complexes that control proteolytic processing of the amyloid precursor protein and Notch. We report here that nicastrin is most probably a type 1 transmembrane glycoprotein that is expressed at moderate levels in the brain and in cultured neurons. Immunofluorescence studies demonstrate that nicastrin is localized in the endoplasmic reticulum, Golgi, and a discrete population of vesicles. Glycosidase analyses reveal that endogenous nicastrin undergoes a conventional, trafficking-dependent maturation process. However, when highly expressed in transfected cells, there is a disproportionate accumulation of the endo-beta-N-acetylglucosaminidase H-sensitive, immature form, with no significant increase in the levels of the fully mature species. Immunoprecipitation revealed that presenilin-1 interacts preferentially with mature nicastrin, suggesting that correct trafficking and co-localization of the presenilin complex components are essential for activity. These findings demonstrate that trafficking and post-translational modifications of nicastrin are tightly regulated processes that accompany the assembly of the active presenilin complexes that execute gamma-secretase cleavage. These results also underscore the caveat that simple overexpression of nicastrin in transfected cells may result in the accumulation of large amounts of the immature protein, which is apparently unable to assemble into the active complexes capable of processing amyloid precursor protein and Notch.

Alzheimer Disease↗

PubMed2002

Did the CP audits promote the enterprises' CP? A case study in Beijing.

Seven enterprises that have had recent Cleaner Production (CP) audits in Beijing were interviewed to identify whether these enterprises implemented the audit recommendations. If enterprises did implement the recommendations, their reasons and the results were analyzed. Finally, some suggestions on how to promote enterprise-wide CP were given.

China↗

PubMed2002

[Production of chitosan used for flocculant in medium scale].

After the preparing chitosan in laboratory scale, the production of chitosan used for flocculant in medium scale was carried out. The optimum processes for producing chitosan in the three steps of reaction including removal calcium, removal protein and deacetylation were obtained. Comparing with the other methods for producing chitosan, the cost of this method cut down 22%, the production period shortened 66%, and the main properties were closed to or exceeded the commercial chitosan products.

Acetylation↗

PubMed2002

Transport and fate of organochlorine pesticides in the River Wuchuan, southeast China.

Persistent organic pollutants (POPs) such as chlorinated pesticides are of global concern due to their widespread occurrence, persistence, bioaccumulation and toxicity to animals and human. This paper summarises recent research on 18 chlorinated pesticides in an important catchment in China, by determining their concentrations and behaviour in water, sediment, soil and plants. The concentrations of the total pesticides were in the ranges 187-893 ng l(-1) in river water, 8.53-210 ng g(-1) dry weight in soil, 2.66-13.45 ng g(-1) dry weight in river sediment, and 651-2823 ng g(-1) dry weight in plants. The predominance of beta-HCH as the major isomer of HCHs in all water, soil, sediment and plant samples was clearly observed, due to beta-HCH's resistance to biodegradation. On average beta-HCH accounted for 44%, 53%, 50%, and 46% of the total HCH concentration in water, soil, sediment and plant, respectively. Of the DDTs, DDE accounted for 48%, 43%, 53%, 55% of the total DDT, which suggested that DDT had been transformed to its metabolites, DDE and DDD, of which DDE was the more stable. The chlorinated pesticide levels in the River Wuchuan were generally below the guideline values in China, but some sites displayed levels in excess of EC Environmental Quality Standards for HCHs and DDTs. The results therefore provide important information on the current contamination status of a key agricultural watershed in China, and point to the need for urgent actions to evaluate the long-term fate and toxicity of such persistent compounds and an appropriate remediation strategy.

Biodegradation, Environmental↗

PubMed2002

The levels of mature glycosylated nicastrin are regulated and correlate with gamma-secretase processing of amyloid beta-precursor protein.

Nicastrin, a type-I transmembrane glycoprotein, is a necessary component of the high molecular weight presenilin (PS) complexes that mediate intramembranous cleavage of beta-amyloid precursor protein (betaAPP) and Notch. Nicastrin undergoes trafficking-dependent glycosylation maturation, and PS1 interacts preferentially with these maturely glycosylated forms of nicastrin. We investigated the effects of differing levels of the immature and mature endoglycosidase-H-resistant forms of nicastrin on Abeta40- and Abeta42-peptide secretion in several cell lines stably expressing a mutant nicastrin (D336A/Y337A) that increases Abeta secretion. There was no correlation between Abeta secretion and the level of over-expression of the immature forms of nicastrin. The total level of mature nicastrin remained constant, but mutant nicastrin replaced endogenous mature nicastrin in varying degrees. Differences in the levels of mature mutant nicastrin positively correlated with Abeta secretion, but did not influence either betaAPP trafficking or processing by alpha- and beta-secretases. Proper trafficking and terminal maturation of nicastrin is therefore a necessary event for the regulated intramembranous proteolysis of betaAPP.

Amino Acid Substitution↗