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Y Hsieh

Publications and source records attributed to Y Hsieh.

At least 19 recordsLinked to original sources
PubMed2007

Effects of entropy on the gas-phase pyrolysis of ethyl N,N-dimethylcarbamate.

In this study, we examined the gas-phase pyrolysis of ethyl N,N-dimethylcarbamate theoretically at various theoretical levels. The reaction consists of a two-step mechanism, with N,N-dimethylcarbamic acid and ethylene as reaction intermediates. In the first step, the reaction proceeds via a six-membered cyclic transition state (TS), which is more favorable than that via a four-membered cyclic TS. Here, the contribution of entropy to the overall potential energy surface was found to play an important role in determining the rate-limiting step, which was found to be the second step when viewed in terms of the enthalpy of activation (DeltaH(not equal)), but the first step when entropy changes (-TDeltaS(not equal)) were considered. These results are consistent with experimental findings. Moreover, the experimental activation entropy can be reproduced by using the hindered rotor approximation, which converts some low vibration frequencies that correspond to internal rotational modes into hindered rotors.

Entropy↗
PubMed2001

Genes for human general transcription initiation factors TFIIIB, TFIIIB-associated proteins, TFIIIC2 and PTF/SNAPC: functional and positional candidates for tumour predisposition or inherited genetic diseases?

TFIIIB, TFIIIC2, and PTF/SNAPC are heteromultimeric general transcription factors (GTFs) needed for expression of genes encoding small cytoplasmic (scRNAs) and small nuclear RNAs (snRNAs). Their activity is stimulated by viral oncogenes, such as SV40 large T antigen and Adenovirus E1A, and is repressed by specific transcription factors (STFs) acting as anti-oncogenes, such as p53 and pRb. GTFs role as final targets of critical signal transduction pathways, that control cell proliferation and differentiation, and their involvement in gene expression regulation suggest that the genes encoding them are potential proto-oncogenes or anti-oncogenes or may be otherwise involved in the pathogenesis of inherited genetic diseases. To test our hypothesis through the positional candidate gene approach, we have determined the physical localization in the human genome of the 11 genes, encoding the subunits of these GTFs, and of three genes for proteins associated with TFIIIB (GTF3BAPs). Our data, obtained by chromosomal in situ hybridization, radiation hybrids and somatic cell hybrids analysis, demonstrate that these genes are present in the human genome as single copy sequences and that some cluster to the same cytogenetic band, alone or in combination with class II GTFs. Intriguingly, some of them are localized within chromosomal regions where recurrent, cytogenetically detectable mutations are seen in specific neoplasias, such as neuroblastoma, uterine leyomioma, mucoepidermoid carcinoma of the salivary glands and hemangiopericytoma, or where mutations causing inherited genetic diseases map, such as Peutz-Jeghers syndrome. Their molecular function and genomic position make these GTF genes interesting candidates for causal involvement in oncogenesis or in the pathogenesis of inherited genetic diseases.

Chromosome Mapping↗
PubMed2001

Treatment of neuroleptic malignant syndrome with subcutaneous apomorphine monotherapy.

A 20-year-old psychiatric patient receiving haloperidol treatment developed acute-onset fever, rigidity, and mental changes. Subcutaneous apomorphine was given alone for treatment. The patient had rapid clinical improvement after the treatment. Serial blood examinations showed decline and subsequent normalization of the creatine phosphokinase levels.

Adult↗
PubMed2001

Cassette-accelerated rapid rat screen: a systematic procedure for the dosing and liquid chromatography/atmospheric pressure ionization tandem mass spectrometric analysis of new chemical entities as part of new drug discovery.

This report addresses the continuing need for increased throughput in the evaluation of new chemical entities (NCEs) in terms of their pharmacokinetic (PK) parameters by describing an alternative procedure for increasing the throughput of the in vivo screening of NCEs in the oral rat PK model. The new approach is called "cassette-accelerated rapid rat screen" (CARRS). In this assay, NCEs are dosed individually (n = 2 rats/compound) in batches of six compounds per set. The assay makes use of a semi-automated protein precipitation procedure for sample preparation in a 96-well plate format. The liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) assay is also streamlined by analyzing the samples as "cassettes of six". Using this new approach, a threefold increase in throughput was achieved over the previously reported "rapid rat screen".

Administration, Oral↗
PubMed2001

Quantitative screening and matrix effect studies of drug discovery compounds in monkey plasma using fast-gradient liquid chromatography/tandem mass spectrometry.

A higher-throughput bioanalytical method based on fast-gradient (1 min run time) high-performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS) was developed for screen-type analyses of plasma samples from early drug discovery studies in support of exploratory pharmacodynamic studies. The HPLC system equipped with minibore column was interfaced with either atmospheric pressure chemical ionization (APCI) or electrospray (ESI) ionization techniques. The matrix ion suppression effect of both quantitative HPLC/MS/MS analyses was compared using the post-column infusion system. The use of the described methods provided advantages such as a shorter chromatographic region of ion suppression, less solvent consumption and shorter run times in comparison with standard analytical column HPLC/MS/MS methods. The analytical results obtained by both HPLC/MS/MS methods were in good agreement (within 15% of error) and displayed a good correlation with the pharmacodynamic outcome.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed2001

Direct simultaneous analysis of plasma samples for a drug discovery compound and its hydroxyl metabolite using mixed-function column liquid chromatography-tandem mass spectrometry.

A polymer-coated mixed-function (PCMF) column was evaluated for direct plasma injection for the simultaneous determination of a drug candidate and its hydroxyl metabolite by high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS-MS) in support of pharmacokinetic studies. Each diluted monkey plasma sample containing internal standard was directly injected on to the PCMF column for sample clean-up, enrichment and chromatographic separation. The proteins and macromolecules were first eluted from the column while the drug molecules were retained on the bonded hydrophobic phase. The analytes retained on the column were then eluted with a strong mobile phase using a gradient separation technique at a constant flow rate of 1.0 ml min(-1). When not diverted, the column effluent was connected either to the atmospheric pressure chemical ionization (APCI) source or the electrospray ionization (ESI) source as part of the mass spectrometer system used for quantification. The calibration curve was linear over the range 5-2500 ng ml(-1) for both analytes. The retention times for the analytes and the internal standard were both consistent and no column deterioration was observed for at least 500 injections. The recovery through the column and reproducibility of the dosed compound and its hydroxyl metabolite in monkey plasma samples were > 90% (RSD < 6%). The total analysis time was < 8 min per sample. The analytical results obtained by the proposed direct plasma injection method were in good agreement with those obtained by the conventional LC-MS-MS method.

Chromatography, Liquid↗
PubMed2000

Enzymatic synthesis of cephalothin by penicillin G acylase*

Enzymatic synthesis of cephalothin from 7-aminocephalosporanic acid (7-ACA) and amide derivatives of 2-thienylacetic acid (2-TA) using penicillin G acylase (pen G acylase) was studied. Two amide derivatives of 2-TA namely 2-thienylacetamide (2-TAA) and 2-thienylacetohydroxamic acid (2-TAH) were used in this study. The main reason for choosing amide but not the methyl ester derivative of 2-TA for the enzymatic synthesis was to increase their solubilities in water. The solubility of 2-TA methyl ester (2-TAM), 2-TAA, and 2-TAH in aqueous solution is 8 +/- 0.05 mM, 87 +/- 0.75 mM and 120 +/- 1.65 mM, respectively. Enzymatic conversion of 2-TAH to cephalothin yielded side products but they were not found in the conversion of 2-TAA to cephalothin. The side products were derived from reactions between hydroxyamine and 7-ACA. The effects of pH, temperature, initial substrate concentrations and reaction time on the conversion of 2-TAA and 7-ACA to cephalothin were examined. The optimum reaction condition was determined at pH 6.5 and 10 approximately 15 degrees C. The best conversion yield of 72% was obtained when the initial concentration of 2-TAA and 7-ACA was at 0.4 M and 0.1 M, respectively. Furthermore, a one-step method was developed to purify cephalothin from the enzymatic reaction mixture with the purity of 91% and the recovery yield of 96%.

Journal Article↗
PubMed2000

Direct analysis of plasma samples for drug discovery compounds using mixed-function column liquid chromatography tandem mass spectrometry.

A sensitive, efficient, high throughput, direct injection bioanalytical method based on a single column and high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS/MS) was developed for pharmacokinetic analysis of early drug discovery compounds in plasma samples. After mixing with a working solution containing an internal standard each plasma sample was directly injected into a polymer-coated mixed-function column for sample cleanup, enrichment and chromatographic separation. The stationary phase incorporates hydrophilic polyoxyethylene groups and hydrophobic groups to the polymer-coated silica. This allows proteins and macromolecules to pass through the column due to restricted access to the surface of the packing while retaining the drug molecules on the bonded hydrophobic phase. The analytes retained in the column with a largely aqueous liquid mobile phase were then chemically separated by switching to a strong organic mobile phase. The column effluent was diverted from waste to the mass spectrometer for analyte detection. Within 200 plasma sample injections the response ratio (analyte vs. internal standard, %CV = 4.6) and the retention times for analyte and internal standard were found consistent and no column deterioration was observed. The recoveries of test compound in various plasma samples were greater than 90%. The total analysis time was </=5 min per sample.

Animals↗
PubMed2000

Comparison of a single half-dose, long-acting form of gonadotropin-releasing hormone analog (GnRH-a) and a short-acting form of GnRH-a for pituitary suppression in a controlled ovarian hyperstimulation program.

OBJECTIVE: To compare the effect of a single low-dose leuprolide acetate depot (LA depot) and leuprolide acetate (LA) on pituitary down-regulation in women undergoing controlled ovarian hyperstimulation (COH). DESIGN: Retrospective study. SETTING: An IVF unit of an academic medical center. PATIENT(S): Women who underwent COH and IVF-ET. INTERVENTION(S): Pituitary down-regulation with half-dose LA depot (1.88 mg sc, group 1) or LA (0.5 mg/d sc, group 2) was started on menstrual days 21-23. MAIN OUTCOME MEASURE(S): The concentrations of estradiol (E(2)), FSH, LH, gonadotropin dosages, the numbers of oocytes retrieved, oocytes fertilized and embryos transferred, and pregnancy rates of the two groups were compared. RESULT(S): A total of 289 patients in group 1 and 158 in group 2 were included. There were no statistically significant differences between the two groups in baseline concentrations of E(2) and FSH, concentrations of E(2), FSH, and LH during hCG administration, gonadotropin dosage, the number of oocytes retrieved, the number of oocytes fertilized and embryos transferred, and pregnancy rates. CONCLUSION(S): Single half-dose LA depot offers a useful alternative for pituitary suppression in ovarian stimulation for IVF.

Adult↗
PubMed2000

Cryopreservation of human spermatozoa within human or mouse empty zona pellucidae.

OBJECTIVE: To compare the empty zona pellucidae (ZP) of different species for use in the cryopreservation of spermatozoa. DESIGN: Prospective study. SETTING: An IVF unit of a medical center. PATIENT(S): Patients with azoospermia, oligoasthenozoospermia, or normal spermatozoa. INTERVENTION(S): Human and mouse ZP were prepared by evacuating the cytoplasm of oocytes or embryos. The evacuated ZP were injected with spermatozoa from patients with severe oligoasthenozoospermia and from healthy, fertile men. After the freezing and thawing procedure, the spermatozoa were aspirated outside the ZP. MAIN OUTCOME MEASURE(S): The number of spermatozoa per ZP, the number of motile sperm before freezing and after thawing, the number of sperm lost per ZP after freezing, and the sperm recovery rate were compared according to the different origins of the ZP and the sperm. RESULT(S): The number of spermatozoa, number of motile sperm before freezing and after thawing, number of sperm lost per ZP, and sperm recovery rate were comparable in all groups. The total mean number of motile sperm before freezing and after thawing, the mean number of nonmotile sperm after thawing, the mean number of sperm lost after thawing, and the sperm recovery rate were 14.5%, 11. 8%, 1.0%, 1.5%, and 82%, respectively. CONCLUSION(S): Zona pellucidae are an ideal vehicle for the cryopreservation of sperm collected by testicular sperm extraction or microsurgical epididymal sperm aspiration or from patients with severe oligoasthenozoospermia. There were no differences when human and mouse ZP were used for sperm storage.

Animals↗
PubMed1998

Crystal structure of Y34F mutant human mitochondrial manganese superoxide dismutase and the functional role of tyrosine 34.

Tyrosine 34 is a prominent and conserved residue in the active site of the manganese superoxide dismutases in organisms from bacteria to man. We have prepared the mutant containing the replacement Tyr 34 --> Phe (Y34F) in human manganese superoxide dismutase (hMnSOD) and crystallized it in two different crystal forms, orthorhombic and hexagonal. Crystal structures of hMnSOD Y34F have been solved to 1.9 A resolution in a hexagonal crystal form, denoted as Y34Fhex, and to 2.2 A resolution in an orthorhombic crystal form, denoted as Y34Fortho. Both crystal forms give structures that are closely superimposable with that of wild-type hMnSOD, with the phenyl rings of Tyr 34 in the wild type and Phe 34 in the mutant very similar in orientation. Therefore, in Y34F, a hydrogen-bonded relay that links the metal-bound hydroxyl to ordered solvent (Mn-OH to Gln 143 to Tyr 34 to H2O to His 30) is broken. Surprisingly, the loss of the Tyr 34 hydrogen bonds resulted in large increases in stability (measured by Tm), suggesting that the Tyr 34 hydroxyl does not play a role in stabilizing active-site architecture. The functional role of the side chain hydroxyl of Tyr 34 can be evaluated by comparison of the Y34F mutant with the wild-type hMnSOD. Both wild-type and Y34F had kcat/Km near 10(9) M-1 s-1, close to diffusion-controlled; however, Y34F showed kcat for maximal catalysis smaller by 10-fold than the wild type. In addition, the mutant Y34F was more susceptible to product inhibition by peroxide than the wild-type enzyme. This activity profile and the breaking of the hydrogen-bonding chain at the active site caused by the replacement Tyr 34 --> Phe suggest that Tyr 34 is a proton donor for O2* - reduction to H2O2 or is involved indirectly by orienting solvent or other residues for proton transfer. Up to 100 mM buffers in solution failed to enhance catalysis by either Y34F or the wild-type hMnSOD, suggesting that protonation from solution cannot enhance the release of the inhibiting bound peroxide ion, likely reflecting the enclosure of the active site by conserved residues as shown by the X-ray structures. The increased thermostability of the mutant Y34F and equal diffusion-controlled activity of Y34F and wild-type enzymes with normal superoxide levels suggest that evolutionary conservation of active-site residues in metalloenzymes reflects constraints from extreme rather than average cellular conditions. This new hypothesis that extreme rather than normal substrate concentrations are a powerful constraint on residue conservation may apply most strongly to enzyme defenses where the ability to meet extreme conditions directly affects cell survival.

Binding Sites↗
PubMed1998

Probing the active site of human manganese superoxide dismutase: the role of glutamine 143.

Structural and biochemical characterization of the nonliganding residue glutamine 143 near the manganese of human Mn superoxide dismutase (hMnSOD), a homotetramer of 22 kDa, reveals a functional role for this residue. In the wild-type protein, the side-chain amide group of Gln 143 is about 5 A from the metal and is hydrogen-bonded to Tyr 34, which is a second prominent side chain adjacent to the metal. We have prepared the site-specific mutant of hMnSOD with the conservative replacement of Gln 143 --> Asn (Q143N). The crystal structure of Q143N shows that the side-chain amide nitrogen of residue 143 is 1.7 A more distant from the manganese than in the wild-type enzyme. The Tyr 34 side-chain hydroxyl in Q143N is also moved to become 0.6 A more distant from the metal due to an additional water molecule. Differential scanning calorimetry showed that Q143N is slightly more stable than the wild-type enzyme with Tm for the main unfolding transition increased by 2 degrees C to 90.7 degrees C. Pulse radiolysis and stopped-flow spectrophotometry reveal that unlike wild-type hMnSOD, which is strongly inhibited by peroxide, Q143N MnSOD exhibits no product inhibition even at concentrations of O2. - in the millimolar range, and its catalysis follows Michaelis kinetics with no evidence of cooperativity. However, the overall catalytic activity of this mutant was decreased 2-3 orders of magnitude compared with the wild-type MnSOD, which can account for its lack of product inhibition. Q143N MnSOD lacked the visible absorption spectrum typical of wild-type Mn(III)SOD. Also, unlike the wild-type Mn(III)SOD, which is electron paramagnetic resonance (EPR) silent, Q143N MnSOD has a complex EPR spectrum with many resonances in the region below 2250 G. We conclude that the Gln 143 --> Asn mutation has increased the reduction potential of manganese to stabilize Mn(II), indicating that Gln 143 has a substantial role in maintaining a reduction potential favorable for the oxidation and reduction cycles in the catalytic disproportionation of superoxide. A solvent hydrogen isotope effect near 2 for kcat in catalysis by Q143N hMnSOD indicates rate-contributing proton transfers to form product hydroperoxide anion or hydrogen peroxide. The data demonstrate a prominent role for Gln 143 in maintaining the microenvironment of the manganese and in efficient catalysis of superoxide dismutation to oxygen and hydrogen peroxide.

Binding Sites↗
PubMed1998

Effects of ketoconazole on the intestinal metabolism, transport and oral bioavailability of K02, a novel vinylsulfone peptidomimetic cysteine protease inhibitor and a P450 3A, P-glycoprotein dual substrate, in male Sprague-Dawley rats.

We investigated the effects of ketoconazole on the oral bioavailability of morpholine-urea-phenylalanine-homophenylalanine-vinylsulfone-phenyl (K02), a vinylsulfone peptidomimetic cysteine protease inhibitor, and a P450 3A (CYP3A) and P-glycoprotein dual substrate, in male Sprague-Dawley rats, so as to evaluate the roles of CYP3A and P-gp in K02 disposition. Male Sprague-Dawley rats (8-10 wk old, n = 3-6) were administered a single dose of K02 (10 mg/kg) i.v. or (30 mg/kg) p.o. with or without a concomitant oral dose of ketoconazole (20 mg/kg). Blood samples were collected from 2 min to 8 h after administration through a implanted jugular vein cannula. K02 plasma concentrations were determined by liquid chromatography/mass spectrometer/mass spectrometer analysis. Ketoconazole markedly raised the area under the curve of orally administered K02 from 9.4 +/- 4.4 to 102 +/- 24 mg . min/liter and decreased K02 oral plasma clearance from 3810 +/- 1620 to 306 +/- 60 ml/min/kg. With concomitant ketoconazole dosing, the changes of AUC of i.v. administered K02 (from 94 +/- 17 to 107 +/- 14 mg . min/liter) and clearance (from 110 +/- 22 to 95 +/- 13 ml/min/kg) were not significant, although K02 oral bioavailability increased from 2.9 +/- 1.4 to 31.0 +/- 7.5% (P < .001). In summary, ketoconazole, a dual inhibitor of CYP3A and P-glycoprotein, can effectively increase K02 oral bioavailability by inhibiting the CYP3A/P-gp absorption barrier in the small intestine.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Catalytic properties of human manganese superoxide dismutase.

The depletion of superoxide catalyzed by human manganese superoxide dismutase (MnSOD) was observed spectrophotometrically by measuring the absorbance of superoxide at 250-280 nm following pulse radiolysis and by stopped-flow spectrophotometry. Catalysis showed an initial burst of activity lasting approximately 1 ms followed by the rapid emergence of a greatly inhibited catalysis of zero-order rate. These catalytic properties of human MnSOD are qualitatively similar to those reported for MnSOD from Thermus thermophilus (Bull, C., Niederhoffer, E. C., Yoshida, T., and Fee, J. A.(1991) J. Am. Chem. Soc. 113, 4069-4076). However, there are significant quantitative differences; the emergence of the inhibited form is approximately 30-fold more rapid for human MnSOD. The turnover number for human MnSOD at pH 9.4 and 20 degrees C was kcat = 4 x 10(4) s-1 and kcat/Km = 8 x 10(8) M-1 s-1, determined by a simulated fit of the model of Bull et al. (1991) to the pulse radiolysis data. We also report that the maximum of the visible absorption spectrum of human MnSOD (epsilon480 = 525 M-1 cm-1) showed a strong dependence on pH that could be described by an ionization of pKa 9.4 +/- 0.1 with a maximum at low pH.

Base Sequence↗
PubMed1992

Optimal estimate of population age structure with varying vital rates.

The author presents a method for estimating the age distribution of a population under varying vital statistics. "Some mathematical aspects of the method, as well as its applicability, will be discussed and numerical simulation will be run to illustrate the results and to compare the method with the traditional estimate of stable population theory...."

Age Distribution↗
PubMed1991

[[The effect of demographic structural change on labor utilization in Taiwan]].

"The purpose of this study is to examine the effect of demographic structural change on labor utilization in Taiwan.... Both purging method and decomposing rate differences method are used to analyze labor utilization data obtained from reports on the Manpower Utilization Survey from 1980 to 1989. The results suggest that the age-sex composition change of labor force from 1980 to 1989 pushed down the crude rate of labor underutilization in the labor market; the education-sex composition change pulled up crude rate of underutilization; and marital status-sex composition change also pushed down crude underutilization rate. In sum, the demographic structural change of labor force in Taiwan does have [an] obvious impact on labor utilization." (SUMMARY IN ENG)

Age Distribution↗