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B Yan

Publications and source records attributed to B Yan.

At least 73 records · Page 4Linked to original sources
PubMed1999

Asymmetry and direction reversal in fluctuation-induced biased Brownian motion.

The biased movement of a Brownian particle in a periodic potential fluctuating between a flat and a kinked ratchet state, as first studied by Chauwin, Ajdari, and Prost, is examined. The purpose is to study the physical origin of the frequency-dependent direction reversal of the biased Brownian motion in this system. We show that the existence of the directional reversal depends not only on the lengths of the projections of the two ratchet arms on the potential axis (the arm-projection asymmetry), but also the overall spatial geometry of the potential in a period. In particular, we show that the direction reversal can be obtained in this kinked ratchet model even when the two arm projections are equal. Since this two-state model is the simplest to generate direction reversal and particles can be separated more efficiently in a fluctuating potential if direction reversal exists, the results obtained in this study should be useful for future application in particle separation.

Journal Article↗
PubMed1999

Glycerol is a suberin monomer. New experimental evidence for an old hypothesis

The monomer composition of the esterified part of suberin can be determined using gas chromatography-mass spectroscopy technology and is accordingly believed to be well known. However, evidence was presented recently indicating that the suberin of green cotton (Gossypium hirsutum cv Green Lint) fibers contains substantial amounts of esterified glycerol. This observation is confirmed in the present report by a sodium dodecyl sulfate extraction of membrane lipids and by a developmental study, demonstrating the correlated accumulation of glycerol and established suberin monomers. Corresponding amounts of glycerol also occur in the suberin of the periderm of cotton stems and potato (Solanum tuberosum) tubers. A periderm preparation of wound-healing potato tuber storage parenchyma was further purified by different treatments. As the purification proceeded, the concentration of glycerol increased at about the same rate as that of alpha,omega-alkanedioic acids, the most diagnostic suberin monomers. Therefore, it is proposed that glycerol is a monomer of suberins in general and can cross-link aliphatic and aromatic suberin domains, corresponding to the electron-translucent and electron-opaque suberin lamellae, respectively. This proposal is consistent with the reported dimensions of the electron-translucent suberin lamellae.

Journal Article↗
PubMed1999

Evidence for polymorphism in the canine metabolism of the cyclooxygenase 2 inhibitor, celecoxib.

The pharmacokinetics of celecoxib, a cyclooxygenase-2 inhibitor, was characterized in beagle dogs. Celecoxib is extensively metabolized by dogs to a hydroxymethyl metabolite with subsequent oxidization to the carboxylic acid analog. There are at least two populations of dogs, distinguished by their capacity to eliminate celecoxib from plasma at either a fast or a slow rate after i.v. administration. Within a population of 242 animals, 45.0% were of the EM phenotype, 53.5% were of the PM phenotype, and 1.65% could not be adequately characterized. The mean (+/-S.D.) plasma elimination half-life and clearance of celecoxib were 1.72 +/- 0.79 h and 18.2 +/- 6.4 ml/min/kg for EM dogs and 5.18 +/- 1.29 h and 7.15 +/- 1.41 ml/min/kg for PM dogs. Hepatic microsomes from EM dogs metabolized celecoxib at a higher rate than microsomes from PM dogs. The cDNA for canine cytochrome P-450 (CYP) enzymes, CYP2B11, CYP2C21, CYP2D15, and CYP3A12 were cloned and expressed in sf 9 insect cells. Three new variants of CYP2D15 as well as a novel variant of CYP3A12 were identified. Canine rCYP2D15 and its variants, but not CYP2B11, CYP2C21, and CYP3A12, readily metabolized celecoxib. Quinidine (a specific CYP2D inhibitor) prevented celecoxib metabolism in dog hepatic microsomes, providing evidence of a predominant role for the CYP2D subfamily in canine celecoxib metabolism. However, the lack of a correlation between celecoxib and bufuralol metabolism in hepatic EM or PM microsomes indicates that other CYP subfamilies besides CYP2D may contribute to the polymorphism in canine celecoxib metabolism.

Animals↗
PubMed1999

[The protective effects of prompt escharectomy on myocardial injury following burn in rats].

OBJECTIVE: To investigate the protective effects of prompt escharectomy on myocardial injury following severe burns. METHODS: Rats were inflicted with 30% TBSA III degree scald. They were randomly divided into 3 groups: control group (C, n = 10), non-escharectomy group (NE, n = 50), escharectomy group (E, n = 50). In the E group, burn wounds were excised promptly after the injury. The levels of troponin T (TnT) and tumor necrosis factor (TNF) in plasma and TNF in myocardium were measured at 1, 3, 6, 12 and 24 hours postburn. RESULTS: TnT levels increased markedly at 3 hours post burn, plasma TNF levels increased markedly at 6 hours postburn, and TNF levels in myocardium also increased markedly at 12 hours postburn compared with the C group. Although the levels of TnT and TNF were a little lower in NE group than those in E group at 3 hours post burn, the levels of TnT 6 hours postburn and levels of TNF 12 hours postburn were significantly higher in NE group than those in E group. There were good positive correlations between TNF with TnT levels. CONCLUSIONS: TNF played important roles in the pathogenesis of myocardial injury following burns, its level was correlated with the severity of myocardial injury. TNF levels in E group was much lower that in NE group, suggesting that prompt escharectomy could reduce the production and release of inflammatory cytokines, and lessen the myocardial injury induced by uncontrolled inflammatory response.

Animals↗
PubMed1999

[Isolation and identification of a saponine from Patrinia scabiosaefolia].

A saponine compound was isolated from the acetone extract of the roots and rhizomes of Patrinia scabiosaefolia Fish. ex Link. Its structure was identified by combination of chemical reaction and spectrum analysis as 3-O-alpha-L-rhamnopyranosyl-(1-2)-beta-D-xylopyranosyl oleanolic acid (giganteaside D), and part of its 13C-NMR data was revised by the 2D-NMR. The compound was found in the Patrinia for the first time.

Patrinia↗
PubMed1998

The two functional keratin 6 genes of mouse are differentially regulated and evolved independently from their human orthologs.

The type II keratin 6 (K6) features a complex expression pattern, with a constitutive component in a subset of stratified epithelia and an inducible component following injury and other types of acute challenges. Multiple genes encoding highly related K6 isoforms have been described for human and bovine, a unique feature among mammalian keratin genes. Here we report on the cloning and characterization of two functional genes and their cDNAs encoding the K6 isoforms in mouse and two related pseudogenes. A systematic comparison of the mouse and human K6 genes suggests that they evolved independently after these species diverged. The mK6alpha and mK6beta genes are organized in tandem with the same transcriptional orientation in the mouse genome. Similar to the human isoforms, the coding sequences for mK6alpha and mK6beta isoforms show approximately 95% identity. The two mouse K6 genes are differentially regulated at the mRNA level in several stratified epithelia. The mK6alpha isoform mRNA clearly predominates in intact trunk skin of adult mice, where it is restricted to the outer root sheath of hair follicles. Both mRNAs are induced in epidermis and proximal hair follicles as early as 1 h following acute injury or topical application of phorbol esters and subsequently increase to a comparable extent but with different kinetics. These novel findings have important implications for the evolution, regulation, and function of K6 genes in mammalian species.

Amino Acid Sequence↗
PubMed1998

Heterologously expressed inner lipoyl domain of dihydrolipoyl acetyltransferase inhibits ATP-dependent inactivation of pyruvate dehydrogenase complex. Identification of important amino acid residues.

The activity of the pyruvate dehydrogenase multienzyme complex (PDC), which catalyses the oxidation of pyruvate to acetyl-CoA within the mitochondrion, is diminished in animal models of diabetes. Studies with purified PDC components have suggested that the kinases responsible for inactivating the decarboxylase catalytic subunits of the complex are most efficient in their regulatory role when they are bound to dihydrolipoyl acetyltransferase (E2) subunits, which form the structural core of the complex. We report that the addition of an exogenous E2 subdomain (inner lipoyl domain) to an intact PDC inhibits ATP-dependent inactivation of the complex. By combining molecular modelling, site-directed mutagenesis and biophysical characterizations, we have also identified two amino acid residues in this subdomain (Ile229 and Phe231) that largely determine the magnitude of this effect.

Acetyltransferases↗
PubMed1998

[Exploration for an early discriminant model of non-skeletal phase in endemic fluorosis exposed to coal-burning].

OBJECTIVE: To detect, diagnose and treat for endemic fluorosis earlier. METHODS: Six kinds of indices, such as environmental fluoride level, were collected from the population in epidemic and non-epidemic areas of endemic fluorosis with a 1:1 paired-match design. A discriminant analysis model was established by multivariate analysis. Levels of fluoride in environment and biological materials were determined by fluoride electrode method. Living condition of the subjects were measured and interviewed. Function of skeletons and joints was measured. Biochemical and enzyme indices were measured with reagent kits and gel electrophoresis. Other indices were measured by interview. All data collected were analyzed by SAS and MDAS computer software. RESULTS: There was significant overall difference between four kinds of discriminant functions, with an overall agreement of 85.78% (83.33% to 98.86%), based on resubstitution with sampled data. Posterior probabilities for new classification of sampled data automatically and randomly produced from a computer were 86.39% to 99.99%. CONCLUSION: The discriminant functions mentioned above, except for the third one with a too small sample size, can be used in early discrimination of endemic fluorosis caused by exposure to coal burning, or in evaluation for the effectiveness of pharmaceutical therapy, with a power of 95%.

Adolescent↗
PubMed1998

The properties of resin supports and their effects on solid-phase organic synthesis.

Solvated resin supports are important carriers for solid-phase organic synthesis in combinatorial chemistry and high-throughput parallel synthesis. The physical properties of resin, resin swelling and dynamic solvation, effects of solvated supports on synthesis, kinetics, site interaction, and product purity are reviewed. Selective solvation of resin alters the local reactivity and accessibility of the bound substrate and the mobility of the entrapped reagent. Resin solvation changes during the course of the reaction when the attached substrate changes its polarity or other physicochemical properties. Selective adsorption determines the reaction kinetics and the action of a phase-transfer catalyst further improves the reaction on resin. Sites interact with each other in 1% DVB polystyrene resins to varying degrees depending on solvent, resin, and reactivity of the pendant groups. Total site isolation seems only achievable by controlling several factors simultaneously such as lower loading and steric hindrance. Through the proper selection of resin and solvent, alternating solvents to accommodate dynamic solvation of the resin, optimization of kinetics when changing solid supports and a careful control of resin impurities, solid-phase organic synthesis can lead to high quality combinatorial libraries.

Chemistry, Pharmaceutical↗
PubMed1998

[A clinical analysis of 94 cases of recurrent stroke].

Ninety-four cases of recurrent stroke were analyzed retrospectively, and 290 cases of first stroke episode were selected as controls. Results showed that recurrent stroke mainly appeared within the first year after the initial episode males predominant. The clinical manifestations of recurrent stroke were variable and commonly more severe. No significant differences was observed between the groups with respect to a variety of factors including the presence of hypertension, diabetes, history of transient ischemic attack, or familial history of stroke, cardiac attacks, cigarette smoking and/or alcohol consumption. The risk factors for recurrent stroke were discussed.

Cerebral Hemorrhage↗
PubMed1998

[Cloning and mapping of the rpoB gene in M. tuberculosis].

OBJECTIVE: To clone the rpoB gene of M. tuberculosis. METHODS: Screening the rpoB gene of M. tuberculosis from M. tuberculosis genomic DNA library by using the rpoB gene conservative region PCR product as a probe. RESULTS: 411 bp products were seen after amplification of H37Ra DNA. The cloning and sequencing results indicated that the 411 bp products were homogeneous to M. tuberculosis rpoB gene. 12,000 clones of M. tuberculosis genomic DNA library were screened by hybridization using the 411 bp product as a probe and 7 clones seemed positive, 3 clones were real positive after the second hybridization. 1 of them carried a 3.8 kb insert fragment. The preliminary restriction map of the 3.8 kb segment was made. The regions which were found homogeneous to the probe to the end of this cloned fragment were 1 and 2.8 kb. CONCLUSION: In comparison with the open reading frame of H37Rv rpoB gene, the 3.8 kb segment cloned here covers larger portion of entire rpoB gene of M. tuberculosis. This study will provide a useful tool to study the resistant mechanism of rifampin and other rifamycin compounds to M. tuberculosis.

Antibiotics, Antitubercular↗
PubMed1998

[Controlled clinical trial on efficacy of 5-month regimens and whole course intermittent 6-month regimens in treating bacillary pulmonary tuberculosis].

OBJECTIVE: To assess the therapeutic efficacy of rifapentine (L), to reduce the duration of treatment and the frequency of drug administration, and to observe the influence on efficacy and adverse reactions of using pyrazinamide (Z) through whole-course. METHOD: Two 5-month regimens respectively including rifampin (R) and L and two whole course intermittent regimens were designed as following: I: 2SHRZ/3R2H2Z2; II: 2SHRZ/3L1H2Z2; III: 2S3H3R3Z3/4L1H2Z2; IV: 2S3H3R3Z3/4L1H2E2. A total of 366 newly-diagnosed bacillary pulmonary tuberculosis patients were admitted and randomly allocated. RESULTS: 339 cases completed the prescribed short course chemotherapy. The sputum conversion rates at the end of the treatment of groups I, II, III and IV were 97.0%, 94.1%, 100.0% and 97.2% respectively. X-ray resolution rates were 96.0%, 97.6%, 100.0% and 94.4% respectively. Cavity-close rates of the 5-month regimens and the 6-month regimens were 77% and 76%. Comparing the results among groups, there were no statistically significant differences (P > 0.05), and no obvious side-effect was found. 305 patients have been followed up for 3 years since completion of the chemotherapy. The bacteriological relapse and bacteriological relapse with deterioration on chest X-ray in groups I, II, III and IV were seen in 2,3,6 and 3 cases respectively. CONCLUSION: Domestic-made rifapentine is a long-acting, highly effective antituberculosis drug. It is unnecessary to use Z in continuation phase, and it is possible to shorten the duration to 5 months with the appropriate combination of essential drugs, which is worthwhile for further study.

Antitubercular Agents↗