Biomedical subjects

T F Ho

Publications and source records attributed to T F Ho.

At least 19 recordsLinked to original sources

PubMed1995

Production of selenomethionine-labeled recombinant human neutrophil collagenase in Escherichia coli.

Molecular analogs of amino acids can be incorporated into proteins. The amino acid analog selenomethionine (SeMet) has been shown to be efficiently incorporated into the proteins of growing Escherichia coli. SeMet-containing proteins are known to produce sufficiently strong anomalous scatter permitting the solution of the selenomethionyl crystal structure by multiwavelength anomalous diffraction (MAD) techniques. The recombinant protein chosen for these studies is mature, truncated neutrophil collagenase (rmNC-t). The rmNC-t protein is a monomer of 163 amino acid residues featuring one active site and two Met residues. We developed a T7 polymerase expression system allowing incorporation of SeMet into rmNC-t protein produced in E. coli. Substitution of Met with SeMet was accomplished by culturing E. coli DL41(DE3), a SeMet-tolerant strain with metA lesion, in a defined medium containing SeMet as the sole source of Met. The SeMet-labeled rmNC-t was isolated from inclusion bodies by solubilizing in urea, purified by anion column chromatography, and then refolded in the presence of Ca2+ and Zn2+. Analysis of SeMet-labeled rmNC-t demonstrated that Met replacement was 100%. Enzymatic characterization revealed no obvious differences in activity or inhibitor binding between rmNC-t and the SeMet-labeled product. We have produced pure, active SeMet-labeled rmNC-t in sufficient quantities for macromolecular crystallography studies.

Base Sequence↗

PubMed1994

Effect of norathyriol, isolated from Tripterospermum lanceolatum, on A23187-induced pleurisy and analgesia in mice.

A23187-induced pleurisy in the mouse was demonstrated in this study. The protein leakage, leukocyte accumulation, LTB4 and PGE2 production in the pleural cavity of mice were increased by A23187 in a dose-dependent manner. At 7.5 nmole A23187 intrapleural injection, the protein level peaked at 0.5-2 h, PMN leukocytes accumulation peaked at 3-4 h, and LTB4 and PGE2 production peaked at 0.5-1 h. In this in vivo model we investigated the anti-inflammatory effect of norathyriol, isolated from Tripterospermum lanceolatum. A23187-induced protein leakage was reduced by norathyriol (ID50 was about 30.6 mg/kg i.p.), indomethacin and BW755C. A23187-induced PMN leukocytes accumulation was suppressed by norathyriol (ID50 was about 16.8 mg/kg, i.p.) and BW755C, while enhanced by indomethacin. Like BW755C, norathyriol reduced both LTB4 and PGE2 production (ID50 was about 18.6 and 29.1 mg/kg i.p., respectively), while indomethacin reduced PGE2 but not LTB4 generation. We also demonstrated the analgesic effect of norathyriol on the acetic acid-induced writhing response. Acetic acid-induced writhing response was depressed by norathyriol (ID50 was about 27.9 mg/kg i.p.), indomethacin and ibuprofen. These results suggest that norathyriol, like BW755C, might be a dual, yet weak, cyclooxygenase and lipoxygenase pathway blocker. The inhibitory effect of norathyriol on the A23187-induced pleurisy and acetic acid-induced writhing response in mice is proposed to be dependent on the reduction of eicosanoids mediators formation in the inflammatory site.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1994

Structure of human neutrophil collagenase reveals large S1' specificity pocket.

The crystal structure of the catalytic domain of human neutrophil collagenase complexed with a peptide transition state analogue has been determined to a resolution of 2.1 A. The structure of the neutrophil enzyme, when compared with the three dimensional structure of the corresponding human fibroblast collagenase, shows differences in the first, S1', of the three enzyme specificity subsites on the carboxy-terminal side of the substrate scissile bond. The S1' pocket in the neutrophil collagenase is significantly larger than the equivalent site in the fibroblast enzyme, suggesting that the former enzyme has a broader range of possible substrates. Such differences also suggest approaches for the design of selective matrix metalloproteinase inhibitors.

Amino Acid Sequence↗

PubMed1992

Viral E1 and E2 proteins support replication of homologous and heterologous papillomaviral origins.

We have shown that E1 and E2 proteins of human papillomavirus type 11 (HPV-11) were essential to support the replication of the homologous viral origin (ori) in a transient replication assay, similar to reports on bovine papillomavirus type 1 (BPV-1). Unexpectedly, matched or even mixed combinations of E1 and E2 proteins from HPV-11 or BPV-1 replicated either ori in human, monkey, and rodent cell lines of epithelial or fibroblastic lineage, albeit with varied efficiencies. Either set of viral proteins was also able to initiate replication of ori-containing plasmids from many other human and animal papillomaviruses. Thus the interactions among the cis elements and trans factors of papillomaviruses are more conserved than expected from the other members of the papovavirus family, simian virus 40 and polyomavirus, for which large tumor antigen does not replicate a heterologous ori in either permissive or nonpermissive cells. We infer that the stringent species and tissue specificities observed for papillomaviruses in vivo are not entirely due to direct restrictions on viral DNA replication. Rather, transcriptional control of viral gene expression must play a dominant role.

3T3 Cells↗

PubMed1992

Effects of a long-chain fatty amine on mammary carcinogenesis induced in female Sprague-Dawley rats by DMBA.

Reports that protein kinase C is inhibited by sphingosine and other long-chain amines and the suggestion that promotion of mammary carcinogenesis by dietary fat is mediated by protein kinase C prompted us to investigate the effects of a long-chain amine, 1-octadecylamine, on mammary carcinogenesis induced by 7,12-dimethylbenz[a]anthracene in rats fed a high-fat diet. Rats fed the amine sulfate at a level of 0.01% in a semipurified diet containing 20% corn oil developed more tumors than those fed the high-fat diet alone, although body weight gain was inhibited slightly. Rats fed the amine sulfate at 0.1% of the diet developed very few tumors compared with those fed either the high-fat diet or a low-fat diet containing 5% corn oil. At the higher level, the C18 amine also caused a marked inhibition of body weight gain.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1991

Social class distribution of obese Chinese children.

Four hundred and eighty four obese Chinese children who were defined obese by a relative weight of more than 120% of standard weight-for-height had their social status evaluated. The social class of each child was arbitrarily determined according to the father's occupation. The distribution of obese children in various social levels was compared with that of the working population in Singapore. Significantly greater proportions of children were in the upper and middle social classes compared with the general working population. Such trends may be related to the increased affluence of the society and the accompanying changes in life-styles and eating habits, and will influence measures in health education and control of childhood obesity in the future.

Child↗

PubMed1991

Assessment of ventricular septal defect by colour flow mapping.

The purpose of this study was to evaluate the usefulness of colour flow mapping (CFM) in the diagnosis and classification of congenital ventricular septal defect (VSD) and in the confirmation of spontaneous and surgical closure. Between August 1988 and March 1990, a total of 102 patients with isolated VSD (82 preoperative and 20 postoperative), age ranging from one day to 14 years, were subjected to 176 echocardiographic examinations. Sequential cross sectional imaging and CFM were the main modalities of assessment with conventional Doppler interrogation for quantitative measurements. In the preoperative group, there were 56 (68.3%) perimembranous (pm) VSD, 14 (17.1%) muscular (m) VSD and 12 (14.6%) doubly committed subarterial (dcsa) VSD. Ventricular septal defect was detected by CFM only in 88.9% of m/VSD, 57.6% of dcsa/VSD and 11.8% of pm/VSD (p less than 0.01). Spontaneous closure rate was highest in m/VSD (28.6%) followed by pm/VSD (8.9%) (p = 0.05). None of the dcsa/VSD closed as assessed by CFM. In the postoperative group, CFM served to quickly confirm complete closure without residual left to right shunt in 20 patients. In addition, CFM was useful in the assessment of haemodynamics and flow directed Doppler interrogation. Hence, CFM is a useful adjunct to cross sectional imaging in the assessment of children with isolated VSD.

Adolescent↗

PubMed1990

In vitro amplification by polymerase chain reaction of a partial gene encoding the third subtype of alpha-2 adrenergic receptor in humans.

In order to clone the third subtype of human alpha-2 adrenergic receptor, polymerase chain reaction (PCR) was employed. Primer pairs corresponding to the conserved sequences in transmembrane domains III and VI were used to selectively amplify the adrenergic receptor genes of the alpha-2 type from human genomic DNA. Sequence data obtained from a clone PCRA2, 885 bps in length, revealed the presence of significant (80%) homology with the known alpha-2A and 2B subtypes of human in the transmembrane domains, whereas distinct variations were noted in the third cytoplasmic loop. When compared with a recently reported alpha-2 receptor gene of rat, essentially identical sequences were found in the transmembrane domains III-VI, except one amino acid in domain VI. As high as 65% homology was also found in the third cytoplasmic loop. We suggest this in vitro amplified fragment represents the partial gene of the third subtype of alpha-2 adrenergic receptor in human.

Amino Acid Sequence↗

PubMed1989

A novel primase-free form of murine DNA polymerase alpha induced by infection with minute virus of mice.

Two species of DNA polymerase alpha free of primase activity were identified in extracts of Ehrlich mouse cells that had been infected with minute virus of mice. Primase-free forms of DNA polymerase alpha eluted with 150 and 180 mM NaCl during ion-exchange chromatography on DEAE-cellulose columns, exhibited sedimentation coefficients of 11 S and 8.2 S, respectively, and were inhibited by aphidicolin, N2-(p-n-butylphenyl)-9-(2-deoxy-beta-D-ribofuranosyl)guanine 5'-triphosphate, and 2-(p-n-butylanilino)-9-(2-deoxy-beta-D-ribofuranosyl)adenine 5'-triphosphate. The ratio of primase-free DNA polymerase alpha to the DNA polymerase alpha-primase complex increased from 1.5 to greater than 100 during the course of infection, and free primase was produced during the MVM replicative cycle.

Animals↗

PubMed1989

Evaluation of lung function in Singapore obese children.

In this study, 65 obese children with a mean age of 12.1 years and mean relative weight (RW) of 156.1% had their lung function evaluated in comparison to predicted normal values. There were substantial changes in forced expiratory flow rates (FEF's) and maximum voluntary ventilation (MVV), with reductions to between 60% to 70% of predicted normal values. The more obese children (RVV greater than or equal to 150%) had significantly lower FEF's and MVV and a significantly greater proportion of the more obese children had FEF50 and MVV of less than 60% of predicted normal values. The results were suggestive of narrowing of small airways and increased respiratory inertance possibly due to excessive accumulation of fat in the chest wall and abdomen leading to respiratory limitation.

Adolescent↗

PubMed1988