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Biomedical subjects

S T Chen

Publications and source records attributed to S T Chen.

At least 19 recordsLinked to original sources
PubMed1992

Kinetic analysis of duck epsilon-crystallin with L-lactate dehydrogenase activity: determination of kinetic constants and comparison of substrate specificity.

A systematic analysis of the kinetic properties of duck lens epsilon-crystallin with lactate dehydrogenase [LDH, (E.C. 1.1.1.27)] activity was carried out by employing some 19 different alpha-keto acids as substrates for this NADH-dependent LDH-catalyzed reaction. The steady-state Michaelis and catalytic constants (Km, kcat) were determined for a broad range of organic compounds. The results provide important insights regarding the binding and affinity of substrates to active sites of this enzyme crystallin and indicate a great potential for the application of the stable epsilon-crystallin as a catalyst to the synthesis of some important chiral alpha-hydroxyacids in a convenient and efficient way. It is also demonstrated for the first time that in addition to the enzymatic activity of lactate dehydrogenase, duck epsilon-crystallin also possesses the enzymatic activity of malate dehydrogenase.

Animals↗
PubMed1992

Facile synthesis of chiral 2-hydroxy acids catalyzed by a stable duck epsilon-crystallin with endogenous L-lactate dehydrogenase activity.

Duck epsilon-crystallin, an abundant structural protein in lenses of some avian species, was shown to possess a genuine and stable L-lactate dehydrogenase (L-LDH; EC 1.1.1.27) activity suitable for the application to enzyme technology as a catalyst for the synthesis of chiral alpha-hydroxy acids. Two pharmaceutically important intermediates, 2-hydroxy acids (S)-2-hydroxybutanoic acid (S)-2-hydroxypentanoic acid have been synthesized in high yields and optical purity utilizing an in situ NADH regeneration system of duck epsilon-crystallin coupled with formate/formate dehydrogenase. This enzyme system is also shown to offer some advantages over the conventional L-LDH sources from several mammalian species.

Animals↗
PubMed1992

Specific reduction of delta-opioid receptor binding in transfected NG108-15 cells.

We have recently identified and sequenced the cDNA for an opioid-binding protein with homologies to cell adhesion molecules (OBCAM) (Schofield, P. R., McFarlard, K. C., Hayflick, J. S., Wilcox, J. N., Cho, T. M., Roy, S., Lee, N. M., Loh, H. H., and Seeburg, P. H. (1989) EMBO J. 8, 489-495). Several lines of evidence using antibodies suggest that OBCAM may play a functional role in NG108-15 neuroblastoma x glioma cells, a useful model system that contains a homogeneous population of delta-opioid receptors. A logical extension of this research is to further test this hypothesis. As part of this study, NG108-15 cells were stably transfected with either sense or antisense sequences of a portion of pROM, the rat cDNA for OBCAM. [3H] Diprenorphine binding was greatly reduced in antisense-transfected cells relative to non-transfected cells. Binding to alpha 2-adrenergic, muscarinic, and insulin receptors was unaffected. These results further support the notion that OBCAM or its analogue is part (or a subunit) of an opioid receptor. Furthermore, our observation of an apparently specific reduction in opioid binding in these transfected cells suggests that they may provide a novel genetic approach for studying regulation of the opioid receptor in this defined cell line.

Amino Acid Sequence↗
PubMed1992

Specific peptide-bond cleavage by microwave irradiation in weak acid solution.

A rapid and selective peptide-bond cleavage in weak acid, induced by microwave irradiation, has been developed. The specific cleavage sites of peptide bonds located only at the carboxyl- and amino-terminal ends of aspartyl residues along the peptide chain. A systematic study including the time course for the cleavage of various aspartyl-containing peptides, the effect of the acidity of the reaction solution on the completeness of peptide-bond cleavage, and the relationship between the power of microwave irradiation and the reaction time of cleavage are studied.

Amino Acid Sequence↗
PubMed1992

Repression of liver-specific hepatitis B virus enhancer 2 activity by adenovirus E1A proteins.

Two regions of the hepatitis B virus (HBV) genome have been shown to display properties of a transcriptional enhancer. Enhancer 1 is active in most hepatoma lines examined as well as in some non-hepatocyte-derived cell lines. In contrast, enhancer 2 activity is strictly liver specific. In this study, we show that adenovirus E1A expression in the highly differentiated human hepatoma line Huh6 strongly inhibits HBV enhancer 2-stimulated transcription while having no effect on HBV enhancer 1 activity. A sequence motif in HBV enhancer 2 which is essential for its enhancer function is the target for E1A-mediated repression. The repression of HBV enhancer 2 activity is mediated through the N-terminal region of the E1A proteins known to bind a 300-kDa cellular protein. Our results suggest that HBV enhancer function may be modulated by a cellular mechanism similar to E1A-mediated transcriptional repression.

Adenovirus E1A Proteins↗
PubMed1992

Community-based survey on blood pressure, blood biochemistry and dietary habits in Pu-Li, Taiwan.

The target population of this study were all residents over the age of 30 in Pu-Li. Stratified cluster sampling was employed. Household visits were carried out in 1987 by the Yang-Ming Crusade, organized by well-trained medical students of the National Yang-Ming Medical College. A total of 1,738 persons out of a potential 2,573 eligible subjects were contacted by at least one of the two interviews or a blood draw. The crude and adjusted (for vacant households) rates were 68% and 84% respectively. Age, sex, and education were evenly distributed. The distribution of physiological variables and blood biochemistry were as follows: 23.0 +/- 3.2 for body mass index (BMI = kg/m2; men 22.8 +/- 3.0, women 23.2 +/- 3.3), 129.7 +/- 20.7 mmHg for systolic blood pressure (men 130.4 +/- 19.6 mmHg, women 128.9 +/- 21.8 mmHg), 81.9 +/- 12.9 mmHg for diastolic blood pressure (men 82.9 +/- 12.8 mmHg, women 80.9 +/- 12.9 mmHg), 103.6 +/- 29.6 mg/dl for fasting plasma glucose (men 101.8 +/- 21.9 mg/dl, women 105.2 +/- 35.2 mg/dl), 222.1 +/- 57.2 mg/dl for cholesterol (men 221.9 +/- 56.5 mg/dl, women 222.3 +/- 57.9 mg/dl), 162.7 +/- 115.5 mg/dl for triglyceride (men 170.3 +/- 117.1 mg/dl, women 155.7 +/- 113.6 mg/dl), 5.8 +/- 3.0 mg/dl for uric acid (men 6.5 +/- 4.8 mg/dl, women 5.2 +/- 1.5 mg/dl). Blood pressure and blood biochemistry variables were positively associated with age. Comparatively, men had much more unhealthy life styles than women; due to prevalences for cigarette smoking (56.0% vs. 3.0%), alcohol intake (43.8% vs. 6.6%) and betel-nut chewing (18.2% vs. 0.8%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Correlation between sonographic and angiographic findings of extracranial carotid artery disease.

Comparison between sonographic and angiographic findings of the extracranial carotid arteries were made in 68 patients. We used a Diasonic Duplex Ultrasonograph (DRF 400) which combined a real-time B-mode imaging system and a pulsed-wave Doppler spectral analyser. Continuous-wave Doppler was also used to determine ophthalmic artery flow direction. The findings were classified into four categories: (1) normal or less than 10% stenosis, (2) 10-49% stenosis, (3) 50-99% stenosis, (4) and total occlusion. The agreement between the two tests was 0.53 which meant fair agreement beyond chance by Kappa statistics. When angiograms were used as gold standard, the sensitivity of duplex sonography was above 80% in all categories of stenosis, and the overall accuracy and specificity were above 90% in those stenosis greater than 50% and occlusion. We conclude that duplex sonography, a reproducible noninvasive test, is a safe and cost-efficient screening method which can provide a good correlation with angiograms in detecting extracranial carotid artery disease.

Adult↗
PubMed1992

Purification of radioiodinated human insulin by high performance liquid chromatography for a sensitive radioimmunoassay.

The optimal sensitivity of a radioimmunoassay depends on the purity of the radiolabeled antigen. The conventional purification methods are not complete and are time consuming. The combination of a Sep-pak C18 cartridge and high performance liquid chromatography (HPLC) for the purification of 125I-labeled insulin in our study revealed that the Sep-pak cartridge can serve as the preliminary step to remove unreacted radioactive iodide, the reactants, and labeled but presumably damaged materials unadsorbed to the cartridge. The fractions eluted from the Sep-pak containing high radioactivity and high immunoreactivity to the antibody were chosen for further purification by HPLC to eliminate undesirable radiolabeled substances with a lesser immunoreactivity. The purified radiolabeled insulin was used to develop a sensitive radioimmunoassay with detecting limits of 0.03 microU/mL per tube.

Chromatography, High Pressure Liquid↗
PubMed1992

Comparison between carotid duplex sonography and angiography in the diagnosis of extracranial internal carotid artery occlusion.

To determine the diagnostic accuracy of extracranial internal carotid artery (ICA) occlusion by carotid duplex sonography and ophthalmic flow direction, we compared both carotid sonograms and angiograms in 82 cases of ischemic cerebrovascular disease. A total of 157 carotid arteries were available for comparison. The overall diagnostic accuracy of ICA occlusion by duplex scanning was 96% (sensitivity, 83%; specificity, 98%; positive predictive value, 91%), by ophthalmic flow examination, 95% (sensitivity, 79%; specificity, 98%; positive predictive value 86%), and by combined study, 98% (sensitivity, 96%; specificity, 98%; positive predictive value 92%). We recommend that the ophthalmic flow examination should be used in combination with other sonographic methods in detecting extracranial carotid artery disease. The combined study gives higher diagnostic accuracy than the single method. When an occlusion or a tight stenosis is uncertain on carotid sonograms, color Doppler or angiography is indicated for further confirmation.

Adult↗
PubMed1991

Autoradiographic study of the retinal projections in the Chinese pangolin, Manis pentadactyla.

Autoradiography was used to investigate the optic system of the Chinese pangolin, Manis pentadactyla. The pattern of retinal projections in the Chinese pangolin is similar to that described in other mammals. Each retina projects bilaterally to the suprachiasmatic nucleus, dorsal and ventral lateral geniculate nuclei, pretectal area, and superior colliculus (SC). Only contralateral projections are found to the medial, lateral, and dorsal accessory optic nuclei. The large lateral nucleus receives a dense projection from the retina and forms a compact mass on the dorsolateral area of the cerebral peduncle. The lamination of the SC could not be clearly demonstrated in the brain of the Chinese pangolin.

Animals↗
PubMed1991

The prognostic value of blood glucose in patients with acute stroke.

We prospectively studied levels of blood glucose and glycohemoglobin, and their correlations with types, severity, and prognosis of stroke in 37 patients with brain infarction (BI) and 35 patients with brain hemorrhage (BH). We found that in the BH group, patients with an elevated glucose level due to stress, diabetes, or both, had a lower consciousness level on admission, larger hematoma size, higher incidence of rupture into the ventricles, and a worse 1-month outcome than patients with a normal glucose level (p less than 0.05). In patients with BI, however, no significant difference was found as related to levels of glucose, though a difference in 6-month mortality between stress hyperglycemic and normoglycemic patients (p less than 0.05) was found. We conclude that an elevated glucose level is associated with a worse clinical condition, larger hematoma size, higher incidence of rupture into the ventricles, and worse outcome in patients with BH. However, it seems to be the severity of the stroke, not the hyperglycemia, that causes the poor outcome. Hyperglycemia may be an epiphenomenon of stroke severity.

Aged↗
PubMed1991

Application of industrial protease "Alcalase" in peptide synthesis.

An industrial alkaline protease "Alcalase" has been found to be very stable in organic solvents and usable as a catalyst for i) resolution of N-protected amino acids, in both aqueous solution and organic solvent with high yield and optical purity, ii) saponification of Fmoc-peptide esters in high concentration organic solvent iii) kinetically controlled peptide bond formation in ethanol solution, iv) diastereoselective hydrolysis of peptide esters, to prepare optically pure peptides.

Amino Acid Sequence↗
PubMed1990

The human fibroblast adenine nucleotide translocator gene. Molecular cloning and sequence.

The human adenine nucleotide translocator multigene family consists of three transcribed genes and at least seven pseudogenes. We report the cloning and sequencing of the gene expressed in human fibroblasts. Like the other two transcribed genes, it has four exons. The 5'-flanking region of the fibroblast translocase gene contains a functional promoter. The promoter has a TATA motif beginning 30 base pairs upstream of the transcription initiation site and five potential SP1 binding sites, but lacks a canonical CCAAT box immediately upstream of the TATA sequence. Differences among the sequence motifs of the 5'-flanking region of the three human translocase genes could account for differences in their cell type-specific and proliferation-associated expression.

Base Sequence↗
PubMed1990

A human ADP/ATP translocase gene has seven pseudogenes and localizes to chromosome X.

There are at least three transcriptionally active human ADP/ATP translocase genes. We have isolated seven ADP/ATP translocase pseudogenes from recombinant human genomic libraries. Each pseudogene sequence had more than 85% identity with the sequence of the human ADP/ATP translocase cDNA derived from fibroblast mRNA, but each had mutations that precluded synthesis of a functional protein. Using an intron probe derived from a partial clone of the human fibroblast ADP/ATP translocase gene, we localized the gene to chromosome Xq13----Xq25-26. The gene encoding the skeletal muscle translocase has previously been shown to be on chromosome 4. Therefore, the human ADP/ATP translocase genes are members of a multigene family that includes pseudogenes and has been dispersed to at least two chromosomes.

Amino Acid Sequence↗
PubMed1990

Side reaction in peptide synthesis. Formation of oxazolidone derivatives.

2-Oxazolidone derivatives formed through an intramolecular reaction in the process of alkaline treatment of urethane-type N-protected peptides of which the N-terminal residues were Ser or Thr having unprotected hydroxyl groups. In oder to avoid this side reaction, the esters of these peptides could be cleaved by enzymatic hydrolyses instead of saponification.

Chemical Phenomena↗
PubMed1990

Sequence analysis of the human thymidine kinase gene promoter: comparison with the human PCNA promoter.

We report the sequence of 4264 nucleotides of 5' flanking sequence of the human thymidine kinase gene, a gene that is maximally expressed at the G1/S boundary of the cell cycle. The position of nucleotide sequences which can act as binding sites for trans-acting factors, Sp-1, AP-1/jun, AP-2, OTF-1 and CAAT box factors as well as other potential cis-acting sequences have been mapped. The organization of these cis-acting sequences in the promoter of the human PCNA gene (another gene that is maximally expressed at the G1/S boundary) are shown for comparison. The potential role that these sequences may play in the transcriptional regulation of these genes is discussed.

Base Sequence↗
PubMed1990

Early effects of cranial irradiation on hypothalamic pituitary function.

Hypothalamic pituitary functions were studied in 25 patients before and 6 months after cranial irradiation with or without radiosensitizing chemotherapy for nasopharyngeal carcinoma. The estimated average total dose was 5,000 cGy to the hypothalamus and pituitary gland. The radiosensitizing chemotherapy used was endoxan, 4900 +/- 873 mg and/or methotrexate 113 +/- 30 mg. All patients had normal pituitary function before radiotherapy. Six months after radiotherapy, there was a significant increase in baseline serum thyrotropin (TSH) and follicle-stimulating hormone (FSH) levels. The TSH response to thyrotropin-releasing hormone (TRH) was significantly increased, suggesting primary hypothyroidism due to neck irradiation. The peak serum TSH response to TRH became delayed in 21 patients, suggesting a defect in TRH release. In male patients who did not receive radiosensitizing chemotherapy, the FSH response to luteotropic hormone-releasing hormone (LHRH) increased while the luteinizing hormone (LH) response decreased. But in male patients who also received radiosensitizing chemotherapy, both the FSH and LH responses to LHRH increased. The adrenocorticotropic hormone (ACTH) response to ovine corticotropin-releasing hormone (CRH) did not change, while the integrated cortisol response increased. The growth hormone (GH) response to growth hormone-releasing hormone (GRH) did not change. The GH response to insulin tolerance test (ITT) increased and may be explained by the more severe hypoglycemia induced by the same dosage of insulin after radiotherapy or the recovery from the previous wasting caused by radiotherapy. There was no significant increase in serum prolactin. In conclusion, we demonstrated impairment of the hypothalamus-pituitary-endocrine gland axes as early as 6 months after cranial irradiation with or without chemotherapy.

Adolescent↗