Biomedical subjects

H J Yun

Publications and source records attributed to H J Yun.

7 recordsLinked to original sources

PubMed2001

Kinetic mechanism and identification of the active site tyrosine residue in Enterobacter amnigenus arylsulfate sulfotransferase.

Bacterial arylsulfate sulfotransferase (ASST) catalyzes the transfer of a sulfate group from a phenyl sulfate ester to a phenolic acceptor. The kinetic mechanism of Enterobacter amnigenus ASST was determined. Plots of 1/v versus 1/[substrate (A)] at different fixed substrate (B) concentrations gave a series of parallel lines. One of the reaction products, p-nitrophenol, inhibited the enzyme noncompetitively with respect to p-nitrophenyl sulfate, but competitively to alpha-naphthol. These results correspond to a ping pong bi bi mechanism. By site-directed mutagenesis, we substituted each conserved tyrosine residue with phenylalanine. Among the mutants, Y123F showed severely reduced catalytic activity. We conclude that Tyr 123 is an essential active site residue. A mechanistic hypothesis is presented to account for these observations.

Amino Acid Substitution↗

PubMed2001

Cloning, sequence analysis, and characterization of the astA gene encoding an arylsulfate sulfotransferase from Citrobacter freundii.

Arylsulfate sulfotransferase (ASST) transfers a sulfate group from a phenolic sulfate ester to a phenolic acceptor substrate. In the present study, the gene encoding ASST was cloned from a genomic library copy of Citrobacter freundii, subcloned into the vector pGEM3Zf(-) and sequenced. Sequencing revealed two contiguous open reading frames (ORF1 and ORF2) on the same strand and based on amino acid sequence homology, they were designated as astA and dsbA, respectively. The amino acid sequence of astA deduced from C. freundii was highly similar to that of the Salmonella typhimurium, Enterobacter amnigenus, Klebsiella, Pseudomonas putida, and Campylobacter jejuni, encoded by the astA genes. However, the ASST activity assay revealed different acceptor specificities. Using p-nitrophenyl sulfate (PNS) as a donor substrate, alpha-naphthol was found to be the best acceptor substrate, followed by phenol, resorcinol, p-acetaminophen, tyramine and tyrosine.

Amino Acid Sequence↗

PubMed2001

Bacterial arylsulfate sulfotransferase as a reporter system.

To investigate whether the arylsulfate sulfotransferase (ASST) is suitable as a reporter system for monitoring gene expression, a reporter vector carrying the fragments of the astA coding region without the promoter region was constructed and designated as pSY815. As a test of the ASST reporter system's suitability, the regulatory regions of ermC and lacZ were inserted upstream of the coding region of the reporter gene to generate pSY815-EC and pSY815-LZ, respectively. In the absence of the inserted regulatory regions, the plasmids displayed very low background activities in Bacillus subtilis and Escherichia coli. The ASST activity under the control of the ermC regulatory region was increased 4.4-fold in B. subtilis when induced by 0.1 microgml(-1) of erythromycin. These results were consistent with a lacZ reporter gene assay of the ermC regulatory region. Furthermore, we confirmed that the lacZ promoter in E. coli was strongly induced to a 17.9-fold increase by 0.05 mM of isopropyl-beta-D-thiogalactopyranoside (IPTG) in this reporter system. These results indicate that the ASST is a suitable reporter system. The lack of endogenous activity, the simple detection of enzyme activity in the living cell, the commercially available non-toxic substrates, and the high sensitivity make ASST a useful genetic reporter system for monitoring gene expression and understanding gene regulation.

Arylsulfotransferase↗

PubMed2001

Protein structural domain parsing by consensus reasoning over multiple knowledge sources and methods.

Domain parsing, or the detection of signals of protein structural domains from sequence data, is a complex and difficult problem. If carried out reliably it would be a powerful interpretive and predictive tool for genomic and proteomic studies. We report on a novel approach to domain parsing using consensus techniques based on Hidden Markov Models (HMMs) and BLAST searches built from a training set of 1471 continuous structural domains from the Dali Domain Dictionary (DDD). Validation on an independent test sample of family-matched structural domain sequences from the Scop database yields a consensus prediction performance rate of 75.5%, well above the 58% obtained by simple agreement of methods.

Algorithms↗

PubMed2000

CT features of metastatic linitis plastica to the rectum in patients with peritoneal carcinomatosis.

OBJECTIVE: We examined the CT features of 22 patients with metastatic linitis plastica to the rectum. CONCLUSION: Metastatic linitis plastica to the rectum should be considered when CT shows a long segment of circumferential rectal wall thickening, especially in patients with peritoneal carcinomatosis from gastric cancer. In such patients, CT helps avoid unnecessary extensive surgery.

Adult↗

PubMed1999

ERK/MAPK pathway is required for changes of cyclin D1 and B1 during phorbol 12-myristate 13-acetate-induced differentiation of K562 cells.

Phorbol 12-myristate 13-acetate (PMA)-induced differentiation of human erythroleukemic K562 cells is characterized by growth arrest, morphological change, and expression of megakaryocyte-specific proteins. We examined the possible involvement of cell cycle regulators with PMA-induced growth arrest and megakaryocytic differentiation of K562 cells. The concentrations of cyclin D1 and p21Waf1/Cip1 were dramatically increased, whereas those of cyclin B1 and cdc2 were decreased, by PMA treatment. The concentrations of most cyclin-dependent kinases (Cdk2, Cdk4, and Cdk6), however, were unchanged by PMA treatment. PD98059, a specific inhibitor of MEK1, partially prevented the increase in cyclin D1 caused by PMA and fully reversed the down-regulation of cyclin B1 protein seen in response to PMA treatment. Thus, it is demonstrated here that the PMA-mediated changes of cyclin D1 and B1 are the result of a persistent increase in extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) activity.

Cell Cycle↗

PubMed1998

Long-term outcomes of therapeutic pelvic lymphadenectomy for stage I endometrial adenocarcinoma.

OBJECTIVE: The treatment of patients with stage I endometrial adenocarcinoma is often shorter and less expensive if total abdominal hysterectomy (TAH), bilateral salpingo-oophorectomy (BSO), and therapeutic lymphadenectomy are used rather than TAH, BSO, pelvic lymph node sampling, and pelvic external beam radiation. We studied whether the survival and morbidity of patients treated with therapeutic lymphadenectomy are equal to or better than with these alternative treatments. METHODS: We reviewed the medical records of patients with stage I endometrial adenocarcinoma who were enrolled in the MetroHealth Medical Center tumor registry between 1970 and 1993 after undergoing full pelvic lymph node dissection, in addition to total abdominal hysterectomy, bilateral salpingo-oophorectomy, and vaginal brachytherapy. The mean number of resected nodes was 33 (median, 31; interquartile range, 19). Patients were followed for 1. 6-20 years (median, 8 years; interquartile range, 5.8 years). Morbidity and survival rates were compared to published series using similar treatment strategies and to those from studies using pelvic external beam radiation and pelvic lymph node sampling rather than lymphadenectomy. RESULTS: Of 192 patients with pathologic stage I (FIGO 1988) endometrial adenocarcinoma, 178 patients had full pelvic lymph node dissection; 159 patients were evaluable. The 15-year overall survival was 98%; 10- and 15- year disease-free survivals were 96 and 94%, respectively. Overall morbidity was 18% (29/159), and moderate-to-severe morbidity was 13% (21/159). Recurrences were seen in 4.4% (7/159) of patients. Grade and myometrial invasion were not significant predictors of disease-free survival after full pelvic lymph node dissection (grade, P = 0.42; stage, P = 0.67). The results compare favorably with those of similar studies and with studies of pelvic external beam radiation. CONCLUSIONS: Primary surgical management with total abdominal hysterectomy, bilateral salpingo-oophorectomy, therapeutic pelvic lymphadenectomy, and vaginal brachytherapy is a viable and possibly preferable option for patients with stage I endometrial adenocarcinoma.

Adenocarcinoma↗