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Biomedical subjects

T W Tan

Publications and source records attributed to T W Tan.

At least 19 recordsLinked to original sources
PubMed2006

Effects of solid retention time on the performance of submerged anoxic/oxic membrane bioreactor.

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were used simultaneously to investigate the effects of solids retention time (SRT) on organic and nitrogen removal in MBR for treating domestic wastewater. COD removal efficiencies in all reactors were consistently above 94% under steady state conditions. Complete conversion of NH(4+)-N to NO(3-)-N was readily achieved over a feed NH(4+)-N concentration range of 30 to 50 mg/L. It was also observed that SRT did not significantly affect the nitrification in the MBR systems investigated. The average denitrification efficiencies for the 3, 5, 10 and 20 days SRT operations were 43.9, 32.6, 47.5 and 66.5%, respectively. In general, the average effluent nitrogen concentrations, which were mainly nitrate, were about 22.2, 27.6, 21.7 and 13.9 mg/L for the 3, 5, 10 and 20 days SRT systems, respectively. The rate of membrane fouling at 3 days SRT operation was more rapid than that observed at 5 days SRT. No fouling was noted in the 10 days and 20 days SRT systems during the entire period of study.

Bioreactors↗
PubMed2004

ANTIMIC: a database of antimicrobial sequences.

Antimicrobial peptides (AMPs) are important components of the innate immune system of many species. These peptides are found in eukaryotes, including mammals, amphibians, insects and plants, as well as in prokaryotes. Other than having pathogen-lytic properties, these peptides have other activities like antitumor activity, mitogen activity, or they may act as signaling molecules. Their short length, fast and efficient action against microbes and low toxicity to mammals have made them potential candidates as peptide drugs. In many cases they are effective against pathogens that are resistant to conventional antibiotics. They can serve as natural templates for the design of novel antimicrobial drugs. Although there are vast amounts of data on natural AMPs, they are not available through one central resource. We have developed a comprehensive database (ANTIMIC, http://research.i2r. a-star.edu.sg/Templar/DB/ANTIMIC/) of known and putative AMPs, which contains approximately 1700 of these peptides. The database is integrated with tools to facilitate efficient extraction of data and their analysis at molecular level, as well as search for new AMPs. These tools include BLAST, PDB structure viewer and the Antimic profile module.

Animals↗
PubMed2003

Curcumin inhibited the arylamines N-acetyltransferase activity, gene expression and DNA adduct formation in human lung cancer cells (A549).

It is well known that N-acetyltransferase (NAT) plays an important role in the arylamine metabolism. We analysed the response of A549 human lung cancer cells for N-acetylation of 2-aminofluorene (AF) to curcumin. After curcumin treatment, the NAT activity was examined by HPLC, AF-DNA adduct formation was examined by HPLC, and NAT gene expression by polymerase chain reaction were detected. The NAT activity in the human A549 cells and cytosols was suppressed by curcumin in a dose-dependent manner. The results also demonstrated that gene expression (NAT1 mRNA) in human lung A549 tumor cells was inhibited and decreased by curcumin. After the incubation of human lung A549 tumor cells with AF with or without curcumin co-treatment, the cells were recovered and DNA was prepared and hydrolyzed to nucleotides. The adducted nucleotides were extracted into butanol and analyzation of AF-DNA adducts was done by HPLC. The results also demonstrated that curcumin decreases AF-DNA adduct formation in the human lung A549 tumor cells.

Acetylation↗
PubMed2003

Removal of MS2 bacteriophage using membrane technologies.

Removals of MS2 bacteriophage virus using different membrane materials under different operating pressures were investigated. The results obtained in this study suggested that a better log removal in terms of MS2 bacteriophage virus could be achieved using Polyamide RO membrane under the optimum operating pressure of 100 psi. It is further noted that variable MS2 influent concentration levels resulted in corresponding variable log removals of the bacteriophages by the Polyamide RO membrane. The presence of MS2 bacteriophage virus in the effluent could possibly be due to leakage of bacteriophages through the membranes structure. Investigations using SEM and AFM showed that there were gaps or pores present in the membrane structure which were sufficiently large for the MS2 viruses to pass through.

Bacteria, Anaerobic↗
PubMed2002

Effects of veratrine and paeoniflorin on isolated mouse vas deferens.

In this study, we attempted to identify the interactions and mechanisms between veratrine and paeoniflorin on isolated mouse vas deferens. Paeoniflorin had no effect on isolated mouse vas deferens. Veratrine (1 x 10(-5) approximately 1 x 10(-3) g/ml) could directly induce contraction of isolated rat and mouse vas deferens. The concentration induced by veratrine (1 x 10(-5) g/ml) was completely inhibited by Ca2+-free solution and verapamil (1 x 10(-5) M), in both the epididymal and the prostatic portions of isolated mouse vas deferens. Naloxone (1 x 10(-5) M) did not alter the contraction induced by veratrine (1 x 10(-5) g/ml) in either the epididymal or the prostatic portions of isolated mouse vas deferens. Paeoniflorin (4.8 x 10(-5) g/ml) inhibited the contraction induced by veratrine (1 x 10(-5) g/ml) in both the epididymal and the prostatic portions of isolated mouse vas deferens. Paeoniflorin (4.8 x 10(-5) g/ml) potentiated norepinephrine (1 x 10(-5) M)-induced phasic contraction in the epididymal portion, but decreased contractions in the prostatic portion. Paeoniflorin (4.8 x 10(-5) g/ml) increased KCI (56 mM)-induced phasic contraction in the epididymal portion, but decreased the tonic contraction in either the epididymal or the prostatic portion. Veratrine (1 x 10(-5) g/ml)-induced contractions could be decreased by pretreatment with ryanodine (1 x 10(-5) M) in both the epididymal and the prostatic portions. Pretreatment with the combination of paeoniflorin (4.8 x 10(-5) g/ml) and ryanodine (1 x 10(-5) M) did not potentiate the inhibition of paeoniflorin in the veratrine-induced contraction in both the epididymal and the prostatic portions of isolated mouse vas deferens.

Animals↗
PubMed2001

Generation of a database containing discordant intron positions in eukaryotic genes (MIDB).

MOTIVATION: Intron sliding is the relocation of intron-exon boundaries over short distances and is often also referred to as intron slippage or intron migration or intron drift. We have generated a database containing discordant intron positions in homologous genes (MIDB--Mismatched Intron DataBase). Discordant intron positions are those that are either closely located in homologous genes (within a window of 10 nucleotides) or an intron position that is present in one gene but not in any of its homologs. The MIDB database aims at systematically collecting information about mismatched introns in the genes from GenBank and organizing it into a form useful for understanding the genomics and dynamics of introns thereby helping understand the evolution of genes. RESULTS: Intron displacement or sliding is critically important for explaining the present distribution of introns among orthologous and paralogous genes. MIDB allows examining of intron movements and allows mapping of intron positions from homologous proteins onto a single sequence. The database is of potential use for molecular biologists in general and for researchers who are interested in gene evolution and eukaryotic gene structure. Partial analysis of this database allowed us to identify a few putative cases of intron sliding. AVAILABILITY: http://intron.bic.nus.edu.sg/midb/midb.html

Amino Acid Sequence↗
PubMed2001

[Analysis of parameters for optimum of ergosterol fermentation].

Parameters in the process of ergosterol fermentation are studied. The relationship between biomass, ergosterol content in Saccharomyces cerevisiae and parameters such as DO, pH, OUR, glucose concentration, are discussed. Because of its good manipulation in yeast fermentation process, Do can thus serve as an effective control parameter. DO at about 12% (+/- 1%) can enhance the total yield of ergosterol considerably.

Ergosterol↗
PubMed2000

A functional significance for codon third bases.

Most amino acids are specified by more than one trinucleotide codon. Here we show that amino acids of differing functional importance may be distinguished by the pattern of synonymous codon usage. GC-rich genes tend to be of a greater transcriptional (p<0.01) and mitogenic (p<0.0001) significance than AT-rich genes, consistent with GC-->AT mutational drift in methylated genomic regions. Third-base GC retention also identifies critical amino acids within individual proteins, as indicated by non-random patterns of codon variation between gene homologs and also by differential sequelae of site-directed mutagenesis. Sequence analysis of human receptor tyrosine kinase genes confirms that functionally important transmembrane hydrophobic amino acids are specified by codons containing GC third bases more often than are transmembrane neutral amino acids (chi(2)=134.2). Amino acids encoded by GC third bases thus appear more tightly linked to cell function and survival than are those encoded by AT third bases.

Amino Acids↗
PubMed2000

ExInt: an Exon/Intron database.

The Exon/Intron (ExInt) database incorporates information on the exon/intron structure of eukaryotic genes. Features in the database include: intron nucleotide sequence, amino acid sequence of the corresponding protein, position of the introns at the amino acid level and intron phase. From ExInt, we have also generated four additional databases each with ExInt entries containing predicted introns, introns experimentally defined, organelle introns or nuclear introns. ExInt is accessible through a retrieval system with pointers to GenBank. The database can be searched by keywords, locus name, NID, accession number or length of the protein. ExInt is freely accessible at http://intron.bic.nus.edu.sg/exint/exint.html

Databases, Factual↗
PubMed2000

IE-Kb: intron exon knowledge base.

SUMMARY: IE-Kb (Intron Exon-Knowledge base) illustrates the intron-exon dynamics in eukaryotic genes. We have developed three different knowledge sets, namely 'Non-redundant ExInt', 'Non-redundant Pfam-ExInt complement' and 'Non-redundant GenBank eukaryotic subdivisional sets' to understand this phenomenon. Statistical analysis is performed on each knowledge set and the results are made available online. The entries in knowledge sets are ranked based on their intron length, exon length and protein length with relational hyper-links to the corresponding intron phase, intron position, intron sequence, gene definition and parent GenBank entry.

Artificial Intelligence↗
PubMed1998

Effects of aspirin on arylamine N-acetyltransferase activity in Klebsiella pneumoniae.

This study was designed to assess the effects of aspirin on arylamine N-acetyltransferase (NAT) activities in the bacterium Klebsiella pneumoniae using high performance liquid chromatography to measure the acetylation of 2-aminofluorene (2-AF) with or without aspirin. Cytosols or suspensions of K. pneumoniae with or without specific concentrations of aspirin co-treatment showed different percentages of 2-AF acetylation. The data indicated that there was decreased NAT activity associated with increased levels of aspirin in K. pneumoniae cytosols and in intact bacteria. For the cytosol examination, the apparent values of Km and Vmax decreased 0.59- and 0.58-fold after co-treated with 40 microM aspirin, respectively, for 2-AF. For the intact bacteria examination, the apparent values of Km and Vmax decreased 0.60- and 0.67-fold after co-treated with 40 microM aspirin, respectively, for 2-AF. This report is the first demonstration to show that aspirin can decrease N-acetyltransferase activity in the bacterium K. pneumoniae.

Acetylation↗
PubMed1998

Integration of bioInformatics tools at the National University of Singapore (NUS).

In the past decade "Big Science" such as the Genome Project has generated an enormous amount of data in the life sciences. Concurrently, the synergy of this project with existing research has quickened the pace of biological discovery. But the major drawback that is beginning to be felt worldwide is the primitive level of organisation in the data accumulated. Without a proper framework or knowledge scaffold to hang and interconnect the various bits of data and information, the national knowledge-to-data ratio is declining rapidly. We are trying to serve a solution to this enigma by providing a World Wide Web (WWW) interface to Biosoftware and at the same time have come up with a database integration tool that can query heterogeneous, geographically scattered and disparate databases simultaneously. In this report we will talk about BioInformatics in general with specific reference to BioInformatics Centre (BIC) at the National University of Singapore.

Computational Biology↗
PubMed1998

Development of software tools at BioInformatics Centre (BIC) at the National University of Singapore (NUS).

There is burgeoning volume of information and data arising from the rapid research and unprecedented progress in molecular biology. This has been particularly affected by the Human Genome Project which is trying to completely sequence three billion nucleotides of the human genome (1),(1a). Other genome sequencing projects are also contributing substantially to this exponential growth in the number of DNA nucleotides and proteins sequenced. The number of journals, reports and research papers and tools required for the analysis of these sequences has also increased. For this the life sciences today needs tools in information technology and computation to prevent degeneration of this data into an inchoate accretion of unconnected facts and figures. The recently formed BioInformatics Centre (BIC) at the National University of Singapore (NUS) provides access to various commonly used computational tools available over the World Wide Web (WWW)--using a uniform interface and easy access. We have also come up with a new database tool. BioKleisli, which allows you to interact with various geographically scattered, heterogeneous, structurally complex and constantly evolving data sources. This paper summarises the importance of network access and database integration to biomedical research and gives a glimpse of current research conducted at BIC.

Animals↗
PubMed1997

Cloning, characterization and expression of a cDNA clone encoding rabbit ubiquitin-conjugating enzyme, E2(32k).

A cDNA clone encoding rabbit E2(32k) was obtained by library screening and PCR. The cDNA contains an open reading frame coding for 238 amino acids which shows an overall identity of 81% to human CDC34, the cell cycle-related ubiquitin-conjugating enzyme. A 50% homology to yeast CDC34 within the conserved core domain was also observed. Northern blot analysis indicated that three transcripts existed in all six rabbit tissues examined but their expression levels varied over a wide range. The putative cDNA coding region was highly expressed in Escherichia coli as a his-tagged protein which was purified to homogeneity. The ability of this expressed protein to form a thiolester bond with ubiquitin showed that it was functionally active. The ability of this protein to catalyze the conjugation of ubiquitin to histone H2A and H2B was also examined.

Amino Acid Sequence↗
PubMed1996

Patient profile and survival in 270 computer tomography-staged patients with nasopharyngeal cancer treated at the Singapore General Hospital.

This is a report analysing the patient profile and survival results in 270 patients with nasopharyngeal carcinoma treated with radiation therapy between July 1987 and December 1988. The patients had a median age of 52.6 months, and a male-female ratio of 2.5:1. Ninety-four percent of patients were Chinese. The commonest presentation was that of a neck mass (found in approximately 65% of patients). Approximately two-thirds presented with disease more advanced than Ho's stage II. At a median follow-up of 52.6 months, the 5-year actuarial survival rate was 53% and the freedom from relapse rate was 57%. One hundred and seven patients died within the observation period. Of these, 46 patients had disease in the post nasal space, 41 in the neck and 60 in sites outside the head and neck.

Actuarial Analysis↗
PubMed1996

Localised nodal non-Hodgkin's lymphoma--a study of 42 cases treated by radiotherapy.

The records of 42 patients with stage I and II nodal non-Hodgkin's lymphoma treated by radiotherapy with and without chemotherapy were analysed with regards to clinical presentation, investigations, treatment, radiotherapy techniques and results. The 5-year overall survival rates for all, low grade, intermediate grade and high grade histology types are 69.5%, 100%, 64.4% and 46.9% respectively. The 5-year relapse-free survival rates of those treated by initial radiotherapy alone for all, low grade and intermediate-high grade histology types are 54.8%, 46.9% and 59.4% respectively.

Adolescent↗
PubMed1996

Testicular seminoma--the results of treatment by radiotherapy in Singapore.

A retrospective analysis was done of 49 patients treated for testicular seminoma over a 15-year period between January 1980 and April 1995 at the Department of Therapeutic Radiology, Singapore General Hospital. Their mean age was 39 years and their median period of follow-up was 67 months. Using the Royal Marsden Staging classification, 35 (71.4%) were stage I, 10 (20.4%) were stage II, I (2%) was stage III, and 3 (6.1%) were stage IV. Five (10.2%) arose in undescended testes. Thirty-six patients were treated with inguinal orchidectomy and postoperative radiotherapy to the para-aortic and ipsilateral iliac nodes. Eight had para-aortic and bilateral iliac irradiation, and 2 had ipsilateral pelvic, para-aortic, mediastinal and supraclavicular lymph node irradiation. Six of the patients had, in addition, irradiation of the inguinal-scrotal area. Nine received both chemotherapy as well as radiotherapy. The median dose of radiation given was 30.67 Gy and where a boost was required, the median total tumour dose was 35.75 Gy. The actuarial relapse-free survival at 10 years was 88.9% and the actuarial overall survival at 10 years was also 88.9%. Long-term treatment toxicities were uncommon.

Actuarial Analysis↗