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Biomedical subjects

K Zeng

Publications and source records attributed to K Zeng.

17 recordsLinked to original sources
PubMed2001

Effect of photosensitizer riboflavin on the fate of 2,4,6-trinitrotoluene in a freshwater environment.

The effect of riboflavin (1 microM) on the fate of TNT (20 mg/l) in a natural water environment was studied. The relative contribution of photolysis, microbial assemblages and freshwater matrix to TNT degradation was examined. The rates, extent and products of TNT and riboflavin transformation were compared under different experimental conditions. It was found that riboflavin significantly enhanced the degradation of TNT in natural water environment. Thus it is a potentially useful photosensitizing agent for the treatment of TNT-contaminated surface water. Furthermore, in the presence of riboflavin, two new intermediates with max. absorption wavelength of 230 nm were found, demonstrating that transformation of TNT in the presence of riboflavin undergoes different pathways.

Biodegradation, Environmental↗
PubMed2000

Amperometric detection of histamine with a methylamine dehydrogenase polypyrrole-based sensor.

Methylamine dehydrogenase (MADH) has been immobilized in a polpyrrole (PPy) film on an electrode surface and used as an amine sensor for the determination of primary amines. Its response to histamine has been characterized in detail. The PPy film containing MADH was formed electrochemically on a gold minielectrode (1-mm diameter) in the presence of ferricyanide. The film was then coated with Nafion. This enzyme electrode did not require any additional cofactors and was not sensitive to oxygen. It exhibited a maximum response current to histamine at applied potentials of 0.24-0.33 V and at pH 7.5-8.5. This MADH-PPy sensor exhibited a response time of less than 3 s. The immobilized MADH on the electrode exhibited Michaelis-Menten behavior similar to that of the free enzyme in solution with a Km value of 1.3 mM. This sensor could be used to reliably detect histamine over a concentration range from approximately 25 microM to 4 mM. This is the first example of a biosensor that uses an immobilized enzyme that possesses the tryptophan tryptophylquinone prosthetic group.

Biosensing Techniques↗
PubMed2000

A new functional domain of guanine nucleotide dissociation inhibitor (alpha-GDI) involved in Rab recycling.

Guanine nucleotide dissociation inhibitor (GDI) is a 55-kDa protein that functions in vesicular membrane transport to recycle Rab GTPases. We have now determined the crystal structure of bovine alpha-GDI at ultra-high resolution (1.04 A). Refinement at this resolution highlighted a region with high mobility of its main-chain residues. This corresponded to a surface loop in the primarily alpha-helical domain II at the base of alpha-GDI containing the previously uncharacterized sequence-conserved region (SCR) 3A. Site-directed mutagenesis showed that this mobile loop plays a crucial role in binding of GDI to membranes and extraction of membrane-bound Rab. This domain, referred to as the mobile effector loop, in combination with Rab-binding residues found in the multi-sheet domain I at the apex of alpha-GDI may provide flexibility for recycling of diverse Rab GTPases. We propose that conserved residues in domains I and II synergize to form the functional face of GDI, and that domain II mediates a critical step in Rab recycling during vesicle fusion.

Amino Acid Motifs↗
PubMed2000

Hepatocyte encapsulation for enhanced cellular functions.

An efficient bioartificial liver-assisted device can sustain the lives of patients with acute liver failure. Among different configurations of the bioreactor design, hepatocyte encapsulation has important features that satisfy most requirements of the device. We have encapsulated rat hepatocytes in a two-layer polymeric membrane by complex coacervation using a simple setup and demonstrated enhanced cellular functions up to three times higher than those of the monolayer control. These microcapsules of the functioning hepatocytes have a 2- to 3-microm outer layer of synthetic polymer with 25% 2-hydroxyethyl methacrylate, 25% methacrylic acid, and 50% methyl methacrylate and an inner layer of positively charged modified collagen as a suitable substrate for the enhanced cellular functions. Permeable only to small molecules up to albumin, the microcapsules should allow unimpeded exchange of nutrients, oxygen, growth factors, and metabolites but prevent attack by immunoglobulins of the immune system, and no "skin effect" of the collagen has been observed. Mechanical properties of the microcapsules measured with a nano-indentation method suggest that the microcapsules should be suitable for use in a bioartificial liver-assisted device.

Animals↗
PubMed2000

[The relationship of polymorphism of angiotensinogen and angiotensin converting enzyme with essential hypertension].

OBJECTIVE: In order to investigate the candidate genes for essential hypertension(EH), the authors determined the frequencies of M235T allele variation in exon 2 of angiotensinogen(AGT) gene and angiotensin converting enzyme (ACE) gene in 95 normotensives and 87 hypertensives in Chinese. METHODS: Polymerase chain reaction combined with restriction enzyme digestion was used to detect the variation AGT gene while PCR was used to determine ACE gene polymorphism. RESULTS: T235 allele frequency was significantly higher in hypertensive patients than in controls (0.45 vs 0.33, P<0. 05) and it was noticeably higher in male hypertensives. The frequency of ACE D allele in the EH patients with family history was higher than that in controls(0.59 vs 0.41,P<0.05). CONCLUSION: The variation of AGT gene was involved in the pathogenesis of hypertension, especially in male. The ACE D allele was associated with EH with family history.

Alleles↗
PubMed1998

Molecular role for the Rab binding platform of guanine nucleotide dissociation inhibitor in endoplasmic reticulum to Golgi transport.

Guanine nucleotide dissociation inhibitor (GDI) regulates the recycling of Rab GTPases involved in vesicle targeting and fusion. We have analyzed the requirement for conserved amino acid residues in the binding of Rab1A and the function of GDI in transport of cargo between the endoplasmic reticulum (ER) and the Golgi apparatus. Using a new approach to monitor GDI-Rab interactions based on the change in fluorescence associated with the release of methylanthraniloyl guanosine di(tri)phosphate-GDP (mGDP) from Rab, we show that residues previously implicated in the binding of the synapse-specific Rab3A, including Gln-236, Arg-240, and Thr-248, are essential for the binding of Rab1A. Mutation of each of these residues has potent effects on the ability of GDI to remove Rab1A from membranes and inhibit ER to Golgi transport in vitro. Given the sequence divergence between Rab1A and 3A (35% identity), these residues are proposed to play a general role in GDI function in the cell. In contrast, several other residues found within or flanking the Rab-binding region were found to have differential effects in the recognition and recycling of Rab1A and 3A, and therefore direct selective interaction of GDI with individual Rab proteins. Intriguingly, mutation of one residue, Arg-70, led to a reduction of Rab1A binding, failed to extract Rab1A from membranes in vitro, yet bound membranes tightly and potently inhibited ER to Golgi transport. These results provide evidence that novel membrane-associated factor(s) mediate Rab-independent GDI interaction with membranes.

Biological Transport↗
PubMed1996

Structure and mutational analysis of Rab GDP-dissociation inhibitor.

The crystal structure of the bovine alpha-isoform of Rab GDP-dissociation inhibitor (GDI), which functions in vesicle-membrane transport to recycle and regulate Rab GTPases, has been determined to a resolution of 1.81 A. GDI is constructed of two main structural units, a large complex multisheet domain I and a smaller alpha-helical domain II. The structural organization of domain I is surprisingly closely related to FAD-containing monooxygenases and oxidases. Sequence-conserved regions common to GDI and the choroideraemia gene product, which delivers Rab to catalytic subunits of Rab geranylgeranyltransferase II, are clustered on one face of the molecule. The two most sequence-conserved regions, which form a compact structure at the apex of GDI, are shown by site-directed mutagenesis to play a critical role in the binding of Rab proteins.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Structural insights into the function of the Rab GDI superfamily.

The 1.81 A crystal structure of Rab GDP-dissociation inhibitor (GDI), a protein that plays a critical role in the recycling of Rab GTPases involved in membrane vesicular transport, has been recently determined. Biochemical studies implicate a highly conserved region involved in Rab binding, which is common to both GDI and the evolutionarily-related choroideremia gene product (CHM/REP) required for Rab prenylation. Here, we summarize the mechanisms by which members of the GDI superfamily might function to coordinate events leading to membrane fusion, and we discuss the unexpected, yet striking structural homology of GDI to FAD-binding proteins.

Adaptor Proteins, Signal Transducing↗
PubMed1996

[Obesity may have more pronounced effect on the occurrence of insulin resistance than hypertension].

OBJECTIVE: To compare the extent of insulin resistance in hypertensive and in obesity patients and verify their role on the occurrence of insulin resistance. METHODS: Insulin sensitivity was assessed by using euglycemic insulin clamp technique (EICT) in normal subjects (NS, n = 36), obesity (n = 23), hypertensive non-obesity patients (HT+nonobesity, n = 51) and hypertensive and obesity patients (HT+obesity, n = 54) Glucose metabolism ratio (M) served as an index of insulin sensitivity. RESULTS: The height sequence of M value was: NS > HT+nonobesity > obesity > HT+obesity (ie, 9.2 +/- 1.0 > 7.6 +/- 2.0 > 6.7 +/- 1.5 > 5.2 +/- 1.8 mg.kg-1.min-1, P < 0.05). The incidence rate of decreased insulin sensitivity among the four groups was: HT+obesity > obesity > HT+nonobesity > NS (87.0%, 69.6%, 41.1% and 2.8%, P < 0.05). After adjusting for age, sex and BMI, M value was greater in normotensives (n = 59) than in hypertension patients (n = 105) (8.0 versus 6.6 mg.kg-1min-1, P < 0.01). Multivariates analysis showed that BMI and SBP are the two most important determinants for M value, but the effect of 1 kg/m2 BMI is equivalent to that of 20 mmHg SBP. CONCLUSION: Decreased insulin sensitivity may be the common linkage between obesity and hypertension. Obesity may have more pronounced effect on insulin sensitivity than hypertension.

Adult↗
PubMed1995

[Intra-aortic balloon pumping in 48 patients with heart failure].

48 patients with heart failure were supported by intra-aortic balloon pumping (IABP) from 1985 to 1993. The disease included rheumatic (39 patients), congenital (7) and coronary hearts (2). The average time of supporting with IABP was 27 hours, 23 patients (48%) survied inclading 19 patients with postoperative lower cardiac output syndrome. Hemodynamics was improved. IABP increased cardiac output syndrome, and hemodynamics was improved. IABP increased cardiac output (50%), cardiac index (60%), stroke volume (50%), stroke volume index (60%) and decreased left atrial pressure or pulmonary wedge pressure. The mortality was 25 patients (52%). The death causes were as follows: arrhythmia (4), renal failure (6), lung failure (2), DIC (1), and the other (12). The main complication of IABP was lower limb ischemia particularly in surgical cut-down method to establish IABP. The analysis indicated that the temporary pacing maker with IABP could prevent some arrhythmia such as frequent premature ventricular beats. Lower limb ischemia and renal failure should receive much attention because they are easy to be confused with shock symptom when IABP.

Adolescent↗
PubMed1994

A surface mutant (G82R) of a human alpha-glutathione S-transferase shows decreased thermal stability and a new mode of molecular association in the crystal.

A chimeric enzyme (GST121) of the human alpha-glutathione S-transferases GST1-1 and GST2-2, which has improved catalytic efficiency and thermostability from its wild-type parent proteins, has been crystallized in a space group that is isomorphous with that reported for crystals of GST1-1. However, a single-site (G82R) mutant of GST121, which exhibits a significant reduction both in vitro and in vivo in protein thermostability, forms crystals that are not isomorphous with GST1-1. The mutant protein crystallizes in space group P2(1)2(1)2(1), with cell dimensions a = 49.5, b = 92.9, c = 115.9 A, and one dimer per asymmetric unit. Preliminary crystallographic results show that a mutation of the surface residue Gly 82 from a neutral to a charged residue causes new salt bridges to be formed among the GST dimers, suggesting that the G82R mutant might aggregate more readily than does GST121 in solution, resulting in a change of its solution properties.

Amino Acid Sequence↗
PubMed1992

Observation of the inverted hexagonal phase of lipids by scanning tunneling microscopy.

Scanning tunneling microscopy (STM) has been used in direct observations of the inverted hexagonal phase of several lipids, such as cardiolipin (CL) in the presence of Ca2+, soybean PE, DOPE and a binary system of CL and DMPC as well. Single tube-like structures, bundles of tubes and the cross-sectional view of the HII phase can clearly be seen at room temperature in a near natural state of these lipids. The success of this study shed some light on the applicability of STM in the investigation of lipid polymorphism and its role in the function of biological membranes.

Cardiolipins↗
PubMed1988

The Abbott IMx automated benchtop immunochemistry analyzer system.

We describe a new clinical laboratory instrument, the IMx, used to automate immunoassay testing in the clinical laboratory. The IMx incorporates a novel technology called Microparticle capture Enzyme ImmunoAssay (MEIA) for assays of high-molecular-mass analytes, and fluorescence polarization immunoassay (FPIA) for hapten assays. A front-surface fluorometer is used to quantify the enzymatic generation of fluorescent product at a rate proportional to the concentration of the analyte in an MEIA, and a fluorescence polarization optical system is used to quantify results in an FPIA. The microprocessor-based instrument uses a robotic arm with two degrees of freedom and a rotating carousel to process the samples for assay. One assay can be done on each of 24 patients' specimens in 30 to 40 min with "walk-away" automation. Calibration curves are stable for at least two weeks. Instrument control involves software-labeled "command keys," a numeric keypad, and an interactive display. Results are output to a thermal printer or computer interface.

Autoanalysis↗
PubMedDate not supplied

Flexure tests on dental ceramics.

The failure stresses in flexural tests of a densely sintered high-purity alumina (Procera AllCeram) were evaluated using three-point bend, ring-on-ring, and piston-on-three-ball tests. Glass-infiltrated presintered alumina (In-Ceram) and leucite-reinforced porcelain (IPS Empress) disks with the same dimensions were also tested using ring-on-ring and piston-on-three-ball tests. The failure stresses for all materials were substantially different (up to 50%) with different testing methods, and cannot be directly compared. However, by considering the effective specimen area under the maximum tensile stress, these failure stress data could be compared. The results emphasize the importance of knowing the test method and the method of calculation when comparing data. These three testing methods were also subjected to Weibull analysis. The Procera AllCeram had a consistently higher failure stress than the other two materials.

Aluminum Oxide↗
PubMedDate not supplied

Evaluation of mechanical properties of dental ceramic core materials in combination with porcelains.

PURPOSE: This paper describes the mechanical testing of dental ceramic core materials in combination with porcelains to simulate the real service conditions for dental applications. MATERIALS AND METHODS: The study included Procera AllCeram (densely sintered high-purity alumina); Vita In-Ceram (glass-infiltrated presintered alumina); three dental porcelains (Procera Porcelain AllCeram, Vitadur-N, and Vitadur Alpha); and densely sintered alumina-Procera Porcelain AllCeram two-layer composites, densely sintered alumina-Vitadur-N two-layer composites, and glass-infiltrated presintered alumina-Vitadur Alpha two-layer composites, with different thicknesses of densely sintered alumina or glass-infiltrated presintered alumina, respectively. The flexural tests were performed in ring-on-ring biaxial bending. The flexural failure stresses were determined using both Timoshenko's biaxial loading equation and Shetty's ring-on-ring stress equation. The bending theory of bilayer plates was used to evaluate the failure stresses in the two-layer composites. Weibull statistics were applied to all stress data, and the information was used to estimate the failure probability at selected applied stresses for a comparison of different two-layer densely sintered alumina-porcelain composites. RESULTS: The failure stress of densely sintered alumina is significantly higher than that of glass-infiltrated presintered alumina as a core dental material under the same testing conditions. The failure stresses of the three commercial dental porcelains are statistically the same. CONCLUSION: The results show that the densely sintered alumina-Procera Porcelain AllCeram two-layer composite has interesting dental applications.

Dental Porcelain↗