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Biomedical subjects

G Choi

Publications and source records attributed to G Choi.

At least 55 records · Page 3Linked to original sources
PubMed1998

Crystal structure and enzyme mechanism of Delta 5-3-ketosteroid isomerase from Pseudomonas testosteroni.

Bacterial Delta 5-3-ketosteroid isomerase (KSI) from Pseudomonas testosteroni has been intensively studied as a prototype for understanding an enzyme-catalyzed allylic rearrangement involving intramolecular proton transfer. Asp38 serves as a general base to abstract the proton from the steroid C4-H, which is a much stronger base than the carboxyl group of this residue. This unfavorable proton transfer requires 11 kcal/mol of energy which has to be provided by favorable interactions between catalytic residues and substrate in the course of the catalytic reaction. How this energy is provided at the active site of KSI has been a controversial issue, and inevitably the enzyme mechanism is not settled. To resolve these issues, we have determined the crystal structure of this enzyme at 2.3 A resolution. The crystal structure revealed that the active site environment of P. testosteroni KSI is nearly identical to that of Pseudomonas putida KSI, whose structure in complex with a reaction intermediate analogue we have determined recently. Comparison of the two structures clearly indicates that the two KSIs should share the same enzyme mechanism involving the stabilization of the dienolate intermediate by the two direct hydrogen bonds to the dienolate oxyanion, one from Tyr14 OH and the other from Asp99 COOH. Mutational analysis of the two residues and other biochemical data strongly suggest that the hydrogen bond of Tyr14 provides the more significant contribution than that of Asp99 to the requisite 11 kcal/mol of energy for the catalytic power of KSI.

Binding Sites↗
PubMed1998

Photoreceptor rhodopsin: structural and conformational study of its chromophore 11-cis retinal in oriented membranes by deuterium solid state NMR.

Rhodopsin is the retinal photoreceptor responsible for visual signal transduction. To determine the orientation and conformation of retinal within the binding pocket of this membrane bound receptor, an ab initio solid state 2H NMR approach was used. Bovine rhodopsin containing 11-cis retinal, specifically deuterated at its methyl groups at the C19 or C20 position, was uniaxially oriented in DMPC bilayers. Integrity of the membranes and quality of alignment were monitored by 31P NMR. Analysis of the obtained 2H NMR spectra provided angles for the individual labelled chemical bond vectors leading to an overall picture for the three dimensional structure of the polyene chain of the chromophore in the protein binding pocket around the Schiff base attachment site.

Animals↗
PubMed1998

Tortuous common carotid artery encountered during neck dissection.

Anomalies of the carotid artery are rare in clinical experience. To our knowledge a tortuous common carotid artery with an abnormal course encountered during neck dissection has never been reported in the available world literature. During dissection of the lower neck in a 60-year-old Korean man, a tortuous right common carotid artery was found to cross over the lower cervical trachea anteriorly and then was positioned in its usual site in the carotid sheath in the mid-neck.

Carcinoma, Squamous Cell↗
PubMed1997

Macroscopic orientation of natural and model membranes for structural studies.

One approach for obtaining high-resolution structural and functional information for biomembranes and their proteins is by static solid-state NMR of oriented systems. Here, a general procedure to align fully functional biological membranes containing large membrane proteins (Mr >30,000) is described. The method, based on the isopotential spin-dry ultracentrifugation technique, relies on the centrifugation of membrane fragments onto a support with simultaneous, or subsequent, partial evaporation of the solvent which aids alignment. The quality of orientation, as shown by the mosaic spread of the samples, was monitored by static solid-state 31P NMR for the phospholipids and by 2H NMR for a deuterated retinal in bovine rhodopsin. The generality of this method is demonstrated with three different membranes containing bovine rhodopsin in reconstituted bilayers, natural membranes with the red cell anion exchange transport protein in erythrocytes, band 3, and the nicotinic acetylcholine receptor.

Animals↗
PubMed1997

Fibrous histiocytoma of the lacrimal sac.

BACKGROUND: Fibrous histiocytoma is a slow-growing tumor that most commonly occurs in the superficial and deep soft tissue, with an occasional occurrence in the orbit. However, fibrous histiocytoma of the lacrimal sac is very rare. METHODS: A case report of a 33-year-old man with a palpable mass in the right lacrimal sac and epiphora is presented, with a review of the literature pertaining to this unusual case. RESULTS: The patient was found to have a 3 x 2-cm-sized mass in the right lacrimal sac. Under the impression of benign tumor, the tumor was excised. Histopathological diagnosis of fibrous histiocytoma was made on the surgical specimen. Following surgical treatment, the patient has remained free of symptoms. CONCLUSIONS: Fibrous histiocytoma of the lacrimal sac is a rare disease. This case report and a review of the literature demonstrated that surgical excision appears to control the tumor.

Adult↗
PubMed1997

Mutational analysis of the three cysteines and active-site aspartic acid 103 of ketosteroid isomerase from Pseudomonas putida biotype B.

In order to clarify the roles of three cysteines in ketosteroid isomerase (KSI) from Pseudomonas putida biotype B, each of the cysteine residues has been changed to a serine residue (C69S, C81S, and C97S) by site-directed mutagenesis. All cysteine mutations caused only a slight decrease in the k(cat) value, with no significant change of Km for the substrate. Even modification of the sulfhydryl group with 5,5'-dithiobis(2-nitrobenzoic acid) has almost no effect on enzyme activity. These results demonstrate that none of the cysteines in the KSI from P. putida is critical for catalytic activity, contrary to the previous identification of a cysteine in an active-site-directed photoinactivation study of KSI. Based on the three-dimensional structures of KSIs with and without dienolate intermediate analog equilenin, as determined by X-ray crystallography at high resolution, Asp-103 was found to be located within the range of the hydrogen bond to the equilenin. To assess the role of Asp-103 in catalysis, Asp-103 has been replaced with either asparagine (D103N) or alanine (D103A) by site-directed mutagenesis. For D103A mutant KSI there was a significant decrease in the k(cat) value: the k(cat) of the mutant was 85-fold lower than that of the wild-type enzyme; however, for the D103N mutant, which retained some hydrogen bonding capability, there was a minor decrease in the k(cat) value. These findings support the idea that aspartic acid 103 in the active site is an essential catalytic residue involved in catalysis by hydrogen bonding to the dienolate intermediate.

Aspartic Acid↗
PubMed1997

Squamous cell carcinoma of the tonsil--clinical features and treatment results.

Squamous cell carcinoma of the tonsil has a relatively poor prognosis. Aggressive surgery, radiation therapy and combinations of irradiation and surgery have been employed but there exists some controversy about the efficacy of these treatment modalities. The purpose of this paper is to compare the efficacy of treatment between the surgery followed by radiation therapy and the preoperative radiation therapy followed by surgical resection. The medical records of 33 patients treated for squamous cell carcinoma of the tonsil at the Department of Otolaryngology-Head and Neck Surgery, Korea University Hospital between 1989-1993 were reviewed retrospectively. None of the patients were stage I, but stage II, III, and IV were four, five, and 24 patients, respectively. There were 30 males and three females. The most common histopathology was moderately differentiated squamous cell carcinoma (20/33). The 13 patients treated initially with surgery had an overall three-year survival rate of 38.5%, and the rate for the 20 patients treated initially with radiation was 40%. The main pattern of treatment failure was a local recurrence and neck metastases, and pathologic differentiation thought to be an important prognostic factor. Complications are fewer in patients treated initially with surgery (23.1%) than patients initially treated with radiation (50.0%). There is no difference in the efficacy between the two therapeutic groups.

Adult↗
PubMed1996

p53 expressions: predicting recurrence and second primary tumors in head and neck squamous cell carcinoma.

BACKGROUND: The survival rate for head and neck squamous cell carcinoma remains poor despite therapeutic advances over the last two decades. For patients with disease confined to the head and neck, there are two major and biologically distinct patterns of treatment failures after definitive therapy: recurrence of primary disease and development of second primary tumors. Understanding the biological basis of patterns of treatment failure after definitive therapy is needed to guide the development of adjuvant treatment and strategies to prevent second primary tumors. PURPOSE: To determine whether expression of the p53 protein has prognostic significance and/or is associated with patterns of treatment failure, we examined protein expression in primary tumor specimens of patients with head and neck squamous cell carcinoma. METHODS: Immunohistochemical analysis with a monoclonal antibody (DO7) specific for p53 protein was used to detect expression of the protein in formalin-fixed, paraffin-embedded tumor samples from 69 head and neck cancer patients treated with definitive local therapy (surgery and/or radiotherapy) between January 1980 and October 1983 at The University of Texas M. D. Anderson Cancer Center. We quantitated p53 protein expression and assessed its association with duration of patient survival, patterns of treatment failure (recurrence of primary tumor and development of second primary tumor), and other clinical parameters. All reported P values resulted from two-sided statistical tests. RESULTS: We found detectable levels of p53 protein expression in the tumor cell nuclei of 41 of 69 patients. Thirty-six (52%) of 69 patients whose tumors exhibited p53 protein expression in greater than or equal to 10% of the cell nuclei were grouped as p53 positive, and 33 (48%) of 69 patients whose tumors exhibited less than 10% nuclear expression were groups as p53 negative. The clinical characteristics of the patients in the p53-positive, and p53-negative groups were well balanced. Overall survival was significantly lower, and the times to tumor recurrence, to second primary tumors, and to any treatment failure were significantly shorter in the p53-positive group that in the p53-negative group (P=.0002, P=.047, P=.003, and P=.0009, respectively), mainly because the p53 positivity was associated with earlier development of tumor recurrence and second primary tumors. The rate of second primary tumor development per person per year was also significantly higher in the p53-positive group that in the p53-negative group. By use of multivariate analysis according to the Cox regression model, p53 expression status was identified as the most significant predictor of overall survival duration (P=.007), time to tumor recurrence (P=.053), time to second primary tumors (P=.035), and time to any treatment failure (P=.004). CONCLUSIONS: The expression of p53 protein in primary head and neck squamous cell carcinoma was significantly predictive of shorter survival because of its association with earlier development of both tumor recurrence and second primary tumors. Thus, p53 expression may be a valuable marker for identifying individuals at high risk of developing a recurrence of primary disease and second primary tumors who may benefit from adjuvant therapy and chemoprevention after definitive local therapy.

Adult↗
PubMed1996

Polysomies of chromosomes 7 and 17 in head and neck squamous cell carcinomas.

OBJECTIVE: To determine the polysomies (ie, cells with > or = 3 chromosome copies) of chromosomes 7 and 17 in tumor tissue, histologically normal epithelia adjacent to the tumor (tumor-adjacent epithelia), and buccal epithelia distant from the tumor (tumor-distant epithelia) of head and neck squamous cell carcinomas. DESIGN: Nonfluorescent, nonisotopic, in situ hybridization using chromosome-specific centromeric DNA probes for chromosomes 7 and 17 was performed on the formalin-fixed, paraffin-embedded specimens from tumor and tumor-adjacent and tumor-distant epithelia of 19 patients with head and neck squamous cell carcinomas and from buccal epithelia of cancer-free control subjects who smoked and did not smoke cigarettes. MAIN OUTCOME MEASURES: Four hundred nuclei in tumor tissue and 200 nuclei in histologically normal epithelia were scored for hybridized signals in each sample. RESULTS: Buccal epithelia of cancer-free control subjects who smoked and did not smoke cigarettes showed no difference in the polysomies of chromosomes 7 and 17, respectively. The polysomies of chromosomes 7 and 17 in the tumor cells were higher than those in the tumor-adjacent epithelia (P < .001 for both), tumor-distant epithelia (P < .001 for both), and buccal epithelia of cancer-free control subjects who smoked and did not smoke cigarettes (P < .001 for both). The polysomies of chromosomes 7 and 17 in the tumor-adjacent epithelia were higher than those in the tumor-distant epithelia (P < .001 for both) and the control buccal epithelia (P = .002 and P < .001, respectively). The tumor-distant epithelia and the control buccal epithelia for the polysomies of chromosomes 7 and 17 had no differences. CONCLUSIONS: The finding of genotypic abnormalities in the tumor-adjacent epithelia supports the concept of field cancerization. Such genotypic parameters may provide a genetic basis for the development of an early recurrence or second primary tumors after therapeutic treatment of head and neck squamous cell carcinomas.

Aged↗
PubMed1996

Three abundant germ line-specific transcripts in Volvox carteri encode photosynthetic proteins.

Volvox carteri is a multicellular eukaryotic green alga composed of about 2000 cells of only two differentiated types: somatic and germ line. To understand how embryonic cells are assigned either to somatic or germ line fates, we are investigating the regulation of transcripts that are abundant in only one cell type. Here we report the identity of three transcripts that are coordinately expressed at high levels in germ line cells but not in somatic cells. Surprisingly, all three transcripts encode photosynthetic chloroplast proteins (light-harvesting complex protein, oxygen-evolving enhancer protein 3, and ferredoxin-NADP+ reductase) that are transcribed from nuclear genes. We discuss why these mRNAs might be required at high levels in germ line cells and present a hypothesis, suggested by our results, on the evolution of cell specialization in the Volvocales.

Algal Proteins↗
PubMed1996

Age-related changes of IgA immunocytes and serum and salivary IgA after tonsillectomy.

For determining treatment options of tonsillar diseases, the authors compared immunohistochemical differences for IgA immunocytes and measured the changes in concentrations of the serum immunoglobulin A and salivary secretory immunoglobulin A before and after tonsillectomy according to age in 126 cases (60 control cases, 66 tonsillectomy cases). The serum IgA and salivary SIgA concentrations of the control group reached to adult's level at the age of 11 to 13. In the tonsillectomies, the serum IgA concentrations below the age of 10 were higher than that of controls and were decreased to the levels of the controls after tonsillectomy in all ages and the salivary SIgA concentrations were decreased to the levels of the controls at the 30th postoperative day, especially at the age of 5 to 7 and 8 to 10. Morphometric features of tonsils in the group below the age of 8 were more active than those in the group above the age of 8 in the controls. In the tonsillectomies, morphometric features of the tonsils were similar to those in the group above the age of 8, but the reticular part of the crypt epithelium remained significantly. Total number of IgA immunocytes was the highest at the age of 5 to 7 with a decline by age, especially at the age of 19 in the controls. In the tonsillectomy group, the number of IgA immunocytes of the extrafollicular area and the reticular part of crypt epithelium decreased below the levels of the control group. In conclusion, tonsils in preschool children are important as a local immunologic defense mechanism, but no significant changes in the immunologic system occurs after tonsillectomy.

Adolescent↗
PubMed1996

Prenatal and postnatal changes of the human tonsillar crypt epithelium.

The tonsillar crypt shows infiltration of lymphoid cells in the epithelium and the highly porous or discontinuous basement membrane. However, the relationship between developmental period and the significance of the disrupted epithelial basement membrane and infiltration of lymphoid cells within the human tonsillar crypt epithelium is still obscure. The present study was designed to determine the prenatal and postnatal changes of the human tonsillar crypt epithelium in 4 fetuses, 4 neonates, 1 infant, 5 children and 4 adults using immunohistochemical stains with polyclonal anti-laminin and monoclonal anti-type IV collagen antibody, and transmission electron microscope. The tonsillar crypt epithelium from all fetuses and neonates showed infiltration of many lymphoid cells and an intact basement membrane by immunohistochemistry. Transmission electron microscope revealed pores in the basement membrane through which lymphocytes passed. Tonsils from a 4-month-old infant showed focal disruption of the basement membrane by immunohistochemical staining. The tonsils from children and adults showed that there was massive disruption of the basement membrane with lymphoid cell infiltration in the tonsillar crypt epithelium by immunohistochemical staining and transmission electron microscopy. In conclusion, lymphoid cell infiltration and holes of the basement membrane of the tonsillar crypt epithelium are normal developmental findings, whereas disruption of the basement membrane of the tonsillar crypt epithelium is pathological.

Adolescent↗
PubMed1993

Proton NMR lipid profile of Leishmania donovani promastigotes.

The proton nuclear magnetic resonance (NMR) lipid profile of Leishmania donovani was obtained in the one-dimensional and two-dimensional modes. Partial assignments of lipid classes and individual lipids were obtained purely from the proton NMR spectrum of the mixture. A more complete assignment and quantitative analysis was achieved by prior separation of the lipids by high pressure liquid chromatography (HPLC) followed by proton NMR analysis of the fractions. This work showed that proton NMR spectroscopy could facilitate lipid analysis and classification of various parasitic protozoa and serve as a basis for rapid studies of comparative lipid metabolism in parasites.

Animals↗
PubMed1983

[Experimental studies on intermittent intraportal hyperalimentation].

Intravenous hyperalimentation (IVH) needs 24 hour infusion everyday without an interruption. Insulin and glucagon are not physiologically secreted. Metabolic rhythm in the body is changed. Protein synthesis and nitrogen balance may be disturbed. For improvement of the metabolic disturbance in IVH, intermittent intraportal hyperalimentation was investigated. Eight Beagles weighed about 10 kg and mongrel dogs weighed 18 kg were used. Glucose and amino acids were given 12.0 g/kg and 2.5 g/kg, respectively. Those were infused into the portal vein for 10 hours every day. During the next 14 hours infusion was not performed at all. Fat was intravenously given 1.5 g/kg as emulsion every day. The levels of insulin and glucagon in the portal vein and the uptake rate of glucose and amino acids in the liver were investigated during administration of the nutrients. After 30 days the dogs were sacrificed and pathological examination was performed. Insulin and glucagon levels were almost physiologically changed. The uptake rate of amino acids into the liver was a high level of 52%. In spite of low level of 162 in non-protein calorie to nitrogen ratio, nitrogen balance remained in 106 +/- 23 mg/kg/day. The body weight increased by 3.6% on the average (p less than 0.01) and the serum protein levels significantly increased (p less than 0.01). In one out of 8 dogs, minute thrombosis and slight sclerosis of the portal vein were found. The liver showed no histological changes. In conclusion, the intermittent portal hyperalimentation seems to be a possible and excellent method of nutrition.

Amino Acids↗