Biomedical subjects

C H Chung

Publications and source records attributed to C H Chung.

At least 163 records · Page 9Linked to original sources

PubMed1991

Molecular cloning of the ecotin gene in Escherichia coli.

The nucleotide sequence of a 876 bp region in E. coli chromosome that encodes Ecotin was determined. The proposed coding sequence for Ecotin is 486 nucleotides long, which would encode a protein consisting of 162 amino acids with a calculated molecular weight of 18,192 Da. The deduced primary sequence of Ecotin includes a 20-residue signal sequence, cleavage of which would give rise to a mature protein with a molecular weight of 16,099 Da. Ecotin does not contain any consensus reactive site sequences of known serine protease inhibitor families, suggesting that Ecotin is a novel inhibitor.

Amino Acid Sequence↗

PubMed1991

Okadaic acid blocks membrane fusion of chick embryonic myoblasts in culture.

Okadaic acid was found to block membrane fusion of chick embryonic myoblasts in culture. It also induced morphological change of the cells from bipolar to spherical shape. These effects were dose-dependent, and could be reversed upon removal of the drug from the culture medium. It showed, however, no effect on the induction of muscle specific proteins including tropomyosin and creatine kinase. When okadaic acid was treated to the cell lysates, the phosphorylation state of many proteins significantly increased. These results suggest that the inhibition of myoblast fusion by okadaic acid may be mediated by the increase in the phosphorylation of certain, unknown protein(s) that regulate the fusion process.

Adenosine Triphosphate↗

PubMed1991

Molecular cloning and sequence analysis of cDNAs for five major subunits of human proteasomes (multi-catalytic proteinase complexes).

Proteasomes are multicatalytic proteinase complexes consisting of a set of non-identical polypeptide components. Of these multiple components, the nucleotide sequences of five major subunits (named HC2, HC3, HC5, HC8 and HC9) of human proteasomes have been determined from recombinant cDNA clones by screening a human HepG2 hepatoblastoma cell cDNA library with rat proteasome cDNAs isolated previously as probes. The polypeptides deduced from their nucleotide sequences consisted of 263, 234, 241, 255 and 261 amino acid residues with calculated molecular weights of 29,554, 25,897, 26,487, 28,431 and 29,482, respectively, which are encoded by single independent genes. The primary structures of these subunits of human proteasomes closely resemble those of their rat counterparts and show considerably high inter-subunit homology, although the homology of HC5 is relatively low. These findings, together with the structural similarities of other eukaryotic proteasomes including those of Drosophila and yeast (Saccharomyces cerevisiae) support and extend the previously proposed concept that eukaryotic proteasome genes form a multi-gene family with the same evolutionary origin.

Amino Acid Sequence↗

PubMed1991

Protease Do is essential for survival of Escherichia coli at high temperatures: its identity with the htrA gene product.

The DNA encoding protease Do was isolated from an E. coli genomic DNA library in lambda gt11, and cloned into a Bluescript plasmid. The cells transformed with the recombinant plasmid were able to overproduce protease Do and grew normally. A mutant lacking the protease activity was also isolated by interrupting the chromosomal DNA with the kan gene. The mutant showed a prolonged lag period and reduced ability to degrade cell proteins as compared to its wild type. Moreover, they were unable to survive at high temperatures, similarly to the htrA mutants. These results suggest that protease Do may play an important role in the intracellular protein breakdown and is essential for survival at high temperatures. Identity of protease Do with the htrA gene product is discussed.

Bacterial Proteins↗

PubMed1991

Radiotherapy for postoperative recurrent uterine cervical carcinoma.

From January 1980 to December 1985, a total of 110 patients with postoperative recurrent uterine cervical carcinoma were treated with radiotherapy. The mean age was 53 years. Ten patients were excluded due to incomplete treatment. The population was grouped according to the classification by Ciatto et al. into patients with central recurrence (n = 48), with peripheral limited recurrence (n = 43), and with peripheral massive recurrence (n = 9). The midpelvic dose given to patients with central recurrence was 40 to 45 Gy, followed by a boost given either by perineal teletherapy with 30 Gy or brachytherapy with 30 Gy at 0.5 cm. beneath the vaginal mucosa. For the peripheral group, the midpelvic dose was 50 Gy followed by a boost of 10 Gy through reduced portals. Further boost to the vaginal mucosa was given by either of the two methods mentioned above. The overall 5-year survival rate was 28%. In the group with central recurrence, it was 42% and in the group with peripheral recurrence 15%. Sixteen patients had persistent local tumor and 15 patients developed distant metastasis. Complications noted were proctitis (5%), cystitis (2%), vesicovaginal fistula (2%) and rectovaginal fistula (2%). Our data clearly indicate that radiotherapy was effective in controlling central recurrence, but for peripheral recurrence, control rate and prognosis were less favorable.

Adult↗

PubMed1991

Yeast culture to improve intake, nutrient digestibility, and performance by dairy cattle during early lactation.

Twenty-four primiparous Holstein cows were fed corn silage:grain (1:1, DM basis) and hay (.9 kg/d) beginning 30 d prepartum and through wk 18 of lactation. Ten grams of Biomate Yeast Plus (5 X 10(9) cfu of Saccharomyces cerevisiae/g) were top-dressed on the a.m. allotment of corn silage:grain fed to 12 cows. Corn silage:grain was restricted during prepartum and thereafter fed for ad libitum intake. Cows fed supplemental yeast peaked earlier and had a higher milk yield compared with control cows (wk 7, 29.5 kg/d vs. wk 11, 28.7 kg/d). Digestibilities of protein and cellulose were improved in cows fed supplemental yeast, contributing to a greater DMI during the first 6 wk of lactation and a higher average milk yield through wk 18 of lactation compared with control cows (27.2 vs. 26.0 kg/d).

Animals↗

PubMed1991

Results of postoperative radiotherapy for clinical stage Ib uterine cervical carcinoma with evidence of microscopic involvement of surgical margin, parametrium and/or lymph node metastasis.

From January 1979 to September 1985, a total of 125 patients preoperatively staged as International Federation of Gynecology and Obstetrics (FIGO) Ib uterine cervical carcinoma were proven to have either microscopic involvement of the surgical margin, parametrium and/or regional lymph node metastasis histopathologically after radical hysterectomy and pelvic lymphadenectomy. All of these patients were treated postoperatively with radiotherapy because of the above indications. Based on indications of postoperative radiotherapy, patients were divided into 3 major subgroups according to the microscopic involvement: group A patients (50) with microscopic evidence of regional lymph node metastasis only; group B patients (59) with microscopic evidence of parametrial involvement; and group C patients (16) with microscopic infiltration of the surgical margin involving the vaginal cuff. All patients were treated with external irradiation using a Cobalt-60 teletherapy machine. The overall actuarial 5-year survival rate was 62% with a 77% 5-year survival rate for group A, a 50% rate for group B and a 75% rate for group C. Further analysis of the prognostic factors revealed that those with regional lymph node involvement of 4 or less had a better chance of survival than those with lymph node involvement of more than 4. Also those with poorly differentiated squamous cell carcinoma had a lower 5-year survival rate than those with moderately or well-differentiated squamous cell carcinoma. Univariate analysis revealed that hemoglobin values, age, and the time interval from surgery to radiotherapy were not significant prognostic factors.

Adenocarcinoma↗

PubMed1991

Molecular cloning of the yeast proteasome PRS2 gene identical to the suppressor gene scl1+.

The YC7-alpha gene encoding a subunit of yeast proteasomes named PRS2 has been isolated and sequenced. Southern blot analysis after electrophoretic separation of yeast chromosomal DNAs showed that the PRS2 gene is located in chromosome VII, unlike the PRS1 gene for subunit YC1, is located on chromosome XV. Surprisingly, the overall structure of the PRS2 gene was found to be identical to that of the suppressor scl1+ gene restoring the SCL1-1 mutation that suppresses crl3 cycloheximide-resistant, temperature-sensitive lethality. The identity of these two genes indicates that the suppressive role of the scl1+ gene product on crl3 mutation could be attributed to proteasomal function.

Amino Acid Sequence↗

PubMed1991

Induction of protease La under stress and its effect on intracellular proteolysis in Escherichia coli.

Induction of protease La was found to increase to higher extent in E. coli that had been treated with canavanine for longer period. However, hydrolysis of canavanine-containing proteins occurred rapidly but at nearly an identical rate regardless of the period of canavanine-treatment. Exposure of E. coli to heat also raised the level of protease La but showed little effect on overall rate of proteolysis. These results suggest that induction of protease La under stress occurs as a part of heat shock response but not necessarily for elimination of denatured or abnormal proteins.

ATP-Dependent Proteases↗

PubMed1990

Preferential degradation of the KMnO4-oxidized or N-ethylmaleimide-modified form of sarcoplasmic reticulum ATPase by calpain from chick skeletal muscle.

KMnO4 and N-ethylmaleimide at low concentrations (i.e., below 0.2 and 1.5 mM, respectively) are known to interact specifically with four to five sulfhydryl residues per Ca2+/Mg2(+)-ATPase molecule in sarcoplasmic reticulum. Purified calpain preferentially hydrolyzes the ATPase that was treated with either agent but not the native form of the enzyme. Exposure to each agent with increasing concentrations results in a greater loss of the ATPase activity and renders the enzyme more susceptible to calpain. In addition, beta,r-methylene-ATP, when added during the treatment of KMnO4 or N-ethylmaleimide, can partially protect the ATPase against the degradation. These results suggest that the covalent modification at the specific sulfhydryl residues in sarcoplasmic reticulum ATPase may mark the enzyme for degradation by intracellular proteinases, such as calpain.

Animals↗

PubMed1990

Proteasomes are essential for yeast proliferation. cDNA cloning and gene disruption of two major subunits.

The cDNAs encoding two major subunits, named YC1 and YC7-alpha, of yeast proteasomes (multicatalytic proteinase complexes) were isolated and sequenced. As deduced from their nucleotide sequences, YC1 and YC7-alpha consist of 288 and 252 amino acid residues with calculated molecular weights of 31,534 and 27,999, respectively. They showed marked sequence homology to other eukaryotic proteasome components, suggesting that proteasomes are composed of a family of subunits with the same evolutional origin. To obtain information on the physiological role of proteasomes, we disrupted the chromosomal genes of YC1 and YC7-alpha of yeast cells independently, using isolated cDNA clones. Disruption of the coding region of one copy of the YC1 gene in diploid yeast created a recessive lethal mutation, but disruption of the 3'-noncoding region of the gene had no effect on cell proliferation. Disruption of the YC7-alpha gene also had a lethal effect on haploid yeast cells. These findings demonstrated that YC1 and YC7-alpha are both encoded by a single copy gene and that these genes are essential for proliferation of yeast cells.

Amino Acid Sequence↗

PubMed1990

Processing of Ada protein by two serine endoproteases Do and So from Escherichia coli.

Two soluble serine proteases Do and So from Escherichia coli were found to distinctively cleave the purified, 39 kDa Ada protein into fragments with sizes of 12-31 kDa. Protease So appears to generate a C-terminal 19 kDa polypeptide, similarly to OmpT protease. In addition, the purified 19 kDa C-terminal half of Ada protein can be further processed mainly to an 18 kDa fragment by protease So and to a 12 kDa by protease Do. These results suggest that proteases Do and So are involved in endogenous cleavage of Ada protein, which may play a role in down-regulating the adaptive response to alkylating agents.

Bacterial Proteins↗

PubMed1990

Conversion of versiconal acetate to versiconal and versicolorin C in extracts from Aspergillus parasiticus.

The primary product of hydrolysis of versiconal acetate catalyzed by porcine liver esterase and the 35-70% ammonium sulfate fraction from a soluble extract from mycelia of Aspergillus parasiticus was versiconal. Versiconal was stable at neutral pH for several hours and was rapidly converted to versicolorin C by treatment with 0.4 M HCl. The addition of NADPH to the 35-70% ammonium sulfate fraction resulted in conversion of versiconal acetate to both versiconal and versicolorin C. The conversion of versiconal acetate to versicolorin C in the cell-free system is proposed to involve an esterase and an NADPH-dependent cyclase.

Anthraquinones↗

PubMed1990

Versicolorin A hemiacetal, hydroxydihydrosterigmatocystin, and aflatoxin G2 alpha reductase activity in extracts from Aspergillus parasiticus.

Versicolorin A hemiacetal was converted to versicolorin C in cell-free systems from Aspergillus parasiticus. The rate of reaction catalyzed by the 35-70% ammonium sulfate fraction was 0.43 nmol min-1 mg-1 with NADPH as cosubstrate and 0.17 nmol min-1 mg-1 with NADH at 25 degrees C at pH 7.4. The product from incubation of 17-hydroxy-16,17-dihydrosterigmatocystin with the 35-70% ammonium sulfate fraction and NADPH was a polar compound which was converted to dihydrosterigmatocystin by 0.4 M HCl. The polar compound is proposed to be the 14,17-hydrated open-chain derivative of dihydrosterigmatocystin. Aflatoxin G2 alpha was also reduced in this system to a polar product tentatively identified as the 13,16-hydrated open-chain derivative of AFG2. The reductase activity may be involved in the formation of reduced intermediates and aflatoxins in cultures of A. parasiticus.

Alcohol Oxidoreductases↗

PubMed1990

Determinants of magnitude of pseudohyperkalemia in thrombocytosis.

The release of potassium from platelets is a well-known cause of pseudohyperkalemia in thrombocytosis. In predicting the magnitude of pseudohyperkalemia associated with thrombocytosis, previous investigations considered only the amount of potassium released from platelets during blood clotting, although the increment in serum potassium during blood clotting depends on the quantity of potassium released from platelets as well as the volume of distribution of the released potassium, which is inversely proportionate to the hematocrit. The present study proposes a new mathematical formula to predict the magnitude of increase in serum potassium during blood clotting, and accuracy of this formula has been tested in a patient with thrombocytosis.

Humans↗

PubMed1990

Palliative radiotherapy of cerebral metastasis from lung cancer.

Cerebral metastasis is a common manifestation of lung cancer. Presenting signs and symptoms are often grave, and consequently often result in patients being debilitated for the rest of their lives. Radiotherapy has been used to treat a majority of these cases, and is considered as the treatment of choice. At Mackay Memorial Hospital, we collected from 1982 to 1985, the records of 42 lung cancer patients with brain metastasis. All the cases had a histological diagnosis of primary lung cancer; most of them were squamous cell carcinoma and adenocarcinoma; only two cases were small cell carcinoma. The diagnosis of brain metastasis was established by computed tomographic scans of the brain and radioisotopic brain scans. Of the 42 cases, 22 received palliative radiotherapy from a cobalt-60 teletherapy machine to the whole brain for a total dose of 30 Gray (Gy) in 10-15 fractions over a time span of 2 to 3 weeks, while the remaining patients only received medical treatment (e.g. cranial decompression with mannitol, steroids, etc.). Most of the patients have already died. In our study, those who received radiotherapy attained considerable palliation of their symptoms and signs, including improvement of their general performance status and neurological function. Although the treatment did not prolong the patient's survival, it did decrease considerably the disability caused by the metastatic disease.

Adenocarcinoma↗

PubMed1990

Radiotherapy for locally recurrent breast cancer.

A total of 43 breast cancer patients were treated at the Department of Radiation Oncology, Mackay Memorial Hospital from January 1978 to December 1987 for postoperative local-regional recurrence. Twenty-six patients developed local recurrence within 12 months after surgery and 17 patients developed local recurrence after 12 months. The mean age for this group of patients was 52 years (range: 27-82). There were 26 postmenopausal and 17 premenopausal patients. Twenty-four patients had received chemotherapy with cyclophosphamide, methotrexate and 5-fluorouracil (CMF) regimen. Four patients were excluded from this study due to incompletion of radiotherapy. Sites of local recurrence in the remaining 39 patients included: chest wall, single (8) and multiple (4); axilla (7); supraclavicular area (5); chest wall with regional node (11); and multiple regional nodes (4). All were free of distant metastasis at the initiation of radiotherapy. A mean tumor dose of 5000 cGy in 28 fractions was given over a 6-week period to the chest wall and draining lymphatics, using an AECL Theratron 80 or a CGR Alcyon MEV Cobalt-60 unit. The overall local control rate was 72%, and the 5-year local control rate was 59%. Nine patients experienced a second local recurrence, with a median interval of 8 months after radiotherapy. Four of them (4/9) also showed evidence of systemic disease at the same time. Distant metastasis, the major cause of mortality, appeared in 49% of the patients with a median interval of 22.8 months after radiotherapy. The three leading sites of distant metastasis were the bones (42%), lungs (37%) and liver (16%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Separation of yeast proteasome subunits. Immunoreactivity with antibodies against ATP-dependent protease Ti from Escherichia coli.

On two-dimensional gel electrophoresis, proteasomes (multicatalytic proteinase complexes) from the yeast Saccharomyces cerevisiae were separated into a characteristic set of approximately 20 components with molecular weights of 21,000 to 31,000 and isoelectric points of 3.5 to 7.5. The main components were isolated by reverse-phase high performance liquid chromatography on a TSK gel phenyl-5PW RP column and named YC1 to YC11, in order of their elution. Immuno-blot analysis showed that two components (YC1-alpha and YC1-beta) with molecular weights of 30,800 and 28,300 strongly cross-reacted with antibody against the P-component of ATP-dependent protease Ti from Escherichia coli, but no components were found to react with antibodies against the A-component of protease Ti or another ATP-dependent protease La (the Ion gene product) of Escherichia coli. These results indicate a structural relationship between eukaryotic proteasomes and bacterial ATP-dependent protease Ti.

Adenosine Triphosphatases↗