Biomedical subjects

S T Chen

Publications and source records attributed to S T Chen.

At least 163 records · Page 9Linked to original sources

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↗

PubMed1990

Secular trend of growth in Malaysian children.

Over the past hundred years in industrialised countries and recently in some developing countries, children have been getting larger and growing to maturity more rapidly. This paper compares the growth of Malaysian children with similar socioeconomic backgrounds but born about twelve years apart. Data were obtained from records of 227 children born between 1968 and 1973 and 238 children born between 1980 and 1985. The children were followed-up regularly at the University Hospital Child Health Clinic in Kuala Lumpur for a variable period from birth to five years of age. Measurements for their weight, length and head circumference were taken at each visit. There is a directional indication that boys and girls of the 1980-1985 cohort are taller, heavier and have bigger head circumferences from birth to five years of age and the difference widens as the child grows older. This study clearly shows that a positive secular trend has taken place in the last decade, reflecting an improvement of living conditions with time. The factors involved in the positive secular trend are manifold and the most important is probably nutrition.

Age Factors↗

PubMed1990

Growth of weight, length and crown-rump length of Malaysian infants and pre-school children.

126 Malaysian children, 65 boys and 61 girls from higher income families were followed-up regularly from birth to six years of age in the University Hospital, Kuala Lumpur. Their physical growth, development, dietary and illness patterns were measured at each visit. The study confirms the observations of previous studies that boys are, on the average, heavier and taller than girls and that Asians are smaller in size with relatively shorter legs compared with children of European ancestry. These racial differences are due to a combination of genetic and environmental differences. Since there are genetic differences in the size and shape of children, standards applicable to the specific population should be used to obtain the best results when assessing the health of an individual child. The growth charts presented in this paper can be used as standards to monitor the growth of Asian infants and pre-school children.

Age Factors↗

PubMed1990

Growth of head circumference of Malaysian infants and pre-school children.

126 Malaysian children, 65 boys and 61 girls from higher income families were followed-up regularly from birth to six years of age in the University Hospital, Kuala Lumpur. The study confirms the observations of previous studies that growth velocity of head circumference is most rapid during the first few months of infancy and then decreases so that by the fifth year of life the increment is minimal. It also confirms the fact that boys have bigger head circumferences than girls. The paper also presents the head circumference distance and velocity percentile charts which can be used to monitor the head circumference of Malaysian children.

Age Factors↗

PubMed1990

Growth of arm circumference and triceps skinfold of Malay children from birth to six years of age.

126 Malaysian children, 65 boys and 61 girls from higher income families were followed-up regularly from birth to six years of age in the University Hospital, Kuala Lumpur. The study shows that for boys and girls, there is a progressive increase in the left mid-upper arm circumference from birth to six years of age. However the rate of growth is not even, being most rapid during the first four month of infancy, then rapidly decreases during the middle third of infancy and thereafter it decreases slowly and by the second year of life, there is hardly any increase in the arm circumference. The left triceps skinfold thickness curves for boys and girls rise rapidly after birth to reach a peak at about three to five months before commencing to decline and then flatten off from the second year of life. The study also shows that on the whole, boys have slightly bigger arm circumference than girls during the first two years of life. From two years of age, girls on the average have more fat than boys. However this difference is statistically not significant at the ages tested. This paper also presents the left mid-upper arm circumference and left triceps skinfold percentile charts of Malaysian boys and girls from birth to six years of age.

Age Factors↗

PubMed1990

Bone age of Malaysian children aged 12 to 28 months.

Between 1976 and 1979, hand radiographs of 112 Malay children, 55 males and 57 females aged from 12 to 28 months, from higher socio-economic class families were obtained and studied by two radiologists. These children were part of a longitudinal study on growth and development. A total of 268 hand and wrist radiographs were taken, which the radiologists read independently of each other using the Greulich and Pyle Atlas. The bone age was then compared with the chronological age and the difference, if any, was noted and 'scored'. It was found that 83.4% of cases for males and 94.8% of cases for females matched within the +/- 6 months discrepancy range. For practical purposes therefore, our population may use the Greulich-Pyle Atlas with a good degree of confidence. Typical hand radiographs of male and female Malay children at 12, 18 and 24 months of age are also presented and these may be used as standards for Malaysian children at the respective age groups.

Age Determination by Skeleton↗

PubMed1990

Ontogeny of the FMRFamide-immunoreactivity in the rat forebrain and diencephalon.

Ontogeny of the FMRFamide (molluscan cardioexcitatory neuropeptide)-containing structures in the forebrain and diencephalon of the rat was investigated by employing immunohistochemical methods. FMRFamide-like immunoreacted (FMRF-IR) fibers first appeared in the borders of the periventricular zone and the preoptic area at embryonic day 18 (E18). Toward birth, the FMRF-IR fibers gradually increased both in immunoreactivity and in number in these areas. A pronounced increase in FMRF-IR was also found in the septum, the arcuate nucleus, the median eminence, the paraventricular nucleus and the amygdaloid complex. A few FMRF-IR fibers appeared at the prenatal stage in the caudate nucleus, the bed nucleus of the stria terminalis, the dorsomedial nucleus and the cortex. The first FMRFamide-immunoreactive neurons were seen in the caudate-putamen and the amygdaloid complex at E21. These FMRF-IR cells increased in immunoreactivity and a significant number of cells was noted in these nuclei in the adult rat. The highest density of FMRF-IR neurons, especially in the amygdala and tuberal hypothalamic area, was detected at postnatal two weeks (P15). FMRFamide-like immunoreactivity in the forebrain and diencephalon appeared in the cell fibers prior to that observed in the cell bodies. This may suggest that some of the immunoreacted fibers may have originated from the lower areas of the rat brain. High densities of FMRF-IR cells present in the embryonic and early postnatal stages may indicate that FMRFamide is an important factor involved in developmental organization of the central nervous system. These results also indicate a differential genesis of FMRF-IR neuronal groups in different regions.

Amino Acid Sequence↗

PubMed1990

Bone changes in hyperthyroidism--a preliminary study.

Thyrotoxicosis may cause osteopenia and lead to increased risk of fractures. From July 1988 to March 1989, 88 hyperthyroid patients and 65 age, sex matched normal controls were enrolled for lumbar spine bone mineral density (BMD) study. Significantly lower BMD values can be found in premenopausal hyperthyroid women (1.233 gm/cm2 vs 1.317 gm/cm2, p less than p less than 0.05). In the group of thyrotoxicosis, no linear correlation can be found between BMD and the degree of hyperthyroidism (N = 84, r = 0.01 and N = 74, r = 0.054 as comparing BMD to T4 and T3, respectively). After treatment with antithyroid drugs (ATD) for 3 months, BMD did not change significantly (1.258 gm/cm2 vs 1.242 gm/cm2, p = 0.02) in the hyperthyroid patients. Therefore, premenopausal hyperthyroid women have lower BMD than premenopausal euthyroid women. The treatment of hyperthyroidism after 3 months' course did not increase lumbar spine BMD.

Adult↗

PubMed1989

The production of polyclonal and monoclonal antibodies in mice using novel immunization methods.

Two novel immunization methods (intrasplenic and intra-inguinal lymph node) have been developed for the production of polyclonal and monoclonal antibodies in mice. Freund's complete adjuvant and antigen were mixed in the ratio of 1:2 (v/v). Various concentrations of human serum albumin (HSA) were used as antigen. No primary immune response was induced with 0.1 microgram of HSA in either of the methods studied. Intrasplenic immunization resulted in the strongest primary immune responses using all other doses of HSA. The primary immune response induced by intrasplenic immunization with 0.5 microgram of HSA was higher than any response induced by subcutaneous immunization with various doses of HSA. Inguinal lymph node immunization was less effective than intrasplenic immunization but better than subcutaneous immunization with 1-50 micrograms of HSA. Comparisons were also made of the efficacy of different adjuvants when inducing primary immune responses with 1 microgram of HSA. Freund's complete adjuvant resulted in a much stronger response than Freund's incomplete adjuvant and alum. Both intrasplenic and inguinal lymph node immunization using 1-5 micrograms of HSA were able to induce strong primary immune responses. Secondary immunization with either method or intravenous injection 3 days before fusion resulted in a higher frequency of specific monoclonal antibodies.

Adjuvants, Immunologic↗

PubMed1989

Temporary complementation of temperature-sensitive mutants of the cell cycle by transfection with a wild-type or a mutant cDNA of ADP/ATP translocase.

A number of cell-cycle-specific temperature-sensitive (ts) mutants have been isolated from animal cells, especially Syrian hamster cells. These ts mutants, like cell cycle ts mutants of yeast, can be complemented by specific genes, some of which have been molecularly cloned. We have isolated a cDNA clone that complements TK-ts13 cells, but only temporarily. This clone, called B1, differs from a previously isolated clone (Sekiguchi et al.: EMBO Journal 7:1683-1687, 1988) that specifically complements ts13 cells. In addition, B1 also complemented temporarily three other ts mutants of the cell cycle, tsAF8, ts694, and ts550C cells. These mutants have different mutations since, in cell fusion experiments, they complement each other. Sequencing of the B1 cDNA clone revealed that it was a mutant of human ADP/ATP translocase in which some human sequences at the 5' end have been replaced by SV40 sequences. The wild-type translocase was less effective but could still increase the survival time of cell cycle ts mutants at the restrictive temperature. Using the polymerase chain reaction, it was possible to demonstrate that the B1 plasmid is expressed in TK-ts13 cells undergoing temporary complementation.

Amino Acid Sequence↗

PubMed1989

Cranial computed tomography in acute disseminated encephalomyelitis.

Acute disseminated encephalomyelitis (ADEM) is an uncommon inflammatory disorder of the nervous system. The appearance of ADEM on cranial CT scans has rarely been reported. The author reports seven cases in two institutions during a period of seven years. Only four of the seven patients had hypodense lesions in the white matter and six patients showed spotty, nodular, or gyral enhancement after contrast injections. The enhancement resolved with steroid therapy, leaving some persistent hypoattenuated areas even after 10 months follow-up, these findings support the dual components of the pathogenesis of ADEM. The vasculitic component may be responsive to steroids, nevertheless the demyelinating or necrotic areas may not, and the latter may be responsible for the sequelae of ADEM.

Acute Disease↗

PubMed1989

S-phase-specific regulation by deletion mutants of the human thymidine kinase promoter.

The levels of thymidine kinase (TK; EC 2.7.1.21) mRNA were determined in nine established cell lines derived from TK-ts13, a temperature-sensitive mutant cell line that arrests in late G1 phase of the cell cycle at the restrictive temperature. The derivative cell lines carried either a cDNA or a minigene of human TK under the control of TK promoters of different lengths. A tenth cell line carried a human TK cDNA under the control of a simian virus 40 promoter. Two different assays were used to determine the S-phase-specific regulation of human TK mRNA levels in quiescent cells stimulated to proliferate. Results from these two assays indicated that (i) the first two introns of the human TK gene had no effect on the S-phase-specific regulation of TK mRNA levels, although the presence of introns increased the amount of TK mRNA; (ii) similar amounts of TK mRNA were present in cells containing constructs with an 83-base-pair (bp) promoter as with other TK promoters comprising up to approximately 4000 bp of 5' flanking sequence; (iii) a 456-bp promoter was fully S-phase-regulated, whereas the 83-bp promoter was only partially regulated; (iv) a 63-bp promoter was much less regulated than an 83-bp promoter; and (v) the crucial element in the 20-bp fragment comprising bp -83 to -64 has been localized, by site-directed mutagenesis, to the CCAAT element at -70.

Animals↗

PubMed1989

Impact of a school milk programme on the nutritional status of school children.

From the start of the school milk feeding programme in February 1985 to October 1986, a total of 2,766 children aged six to nine years from 12 primary schools in Ulu Selangor were followed-up for about two years. The children's weight and height were monitored at the beginning, in the middle and at the end of the study. The study shows that there is a reduction in the prevalence of protein-energy malnutrition in terms of underweight (15.3% to 8.6%), stunting (16.3% to 8.3%) and wasting (2.6% to 1.7%) from the start of the school feeding programme to two years later. Associated with this there was an improvement in the attendance rate of the children during the same period. As there was no major developmental change in Ulu Selangor during that period, it is likely that the reduction in the prevalence of protein-energy malnutrition and the improvement of the attendance rate among the children are due to the impact of the school milk feeding programme.

Animals↗