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Biomedical subjects

B H Oh

Publications and source records attributed to B H Oh.

At least 73 records · Page 4Linked to original sources
PubMed1997

Assessment of mitral annulus velocity by Doppler tissue imaging in the evaluation of left ventricular diastolic function.

OBJECTIVES: This study assessed the clinical utility of mitral annulus velocity in the evaluation of left ventricular diastolic function. BACKGROUND: Mitral inflow velocity recorded by Doppler echocardiography has been widely used to evaluate left ventricular diastolic function but is affected by other factors. The mitral annulus velocity profile during diastole may provide additional information about left ventricular diastolic function. METHODS: Mitral annulus velocity during diastole was measured by Doppler tissue imaging (DTI) 1) in 59 normal volunteers (group 1); 2) in 20 patients with a relaxation abnormality as assessed by Doppler mitral inflow variables (group 2) at baseline and after saline loading; 3) in 11 patients (group 3) with normal diastolic function before and after intravenous nitroglycerin infusion; and 4) in 38 consecutive patients (group 4) undergoing cardiac catheterization in whom mitral inflow velocity and tau as well as mitral annulus velocity were measured simultaneously. RESULTS: In group 1, mean +/- SD peak early and late diastolic mitral annulus velocity was 10.0 +/- 1.3 and 9.5 +/- 1.5 cm/s, respectively. In group 2, mitral inflow velocity profile changed toward the pseudonormalization pattern with saline loading (deceleration time 311 +/- 84 ms before to 216 +/- 40 ms after intervention, p < 0.001), whereas peak early diastolic mitral annulus velocity did not change significantly (5.3 +/- 1.2 cm/s to 5.7 +/- 1.4 cm/s, p = NS). In group 3, despite a significant change in mitral inflow velocity profile after nitroglycerin, peak early diastolic mitral annulus velocity did not change significantly (9.5 +/- 2.2 cm/s to 9.2 +/- 1.7 cm/s, p = NS). In group 4, peak early diastolic mitral annulus velocity (r = -0.56, p < 0.01) and the early/late ratio (r = -0.46, p < 0.01) correlated with tau. When the combination of normal mitral inflow variables with prolonged tau (> or = 50 ms) was classified as pseudonormalization, peak early diastolic mitral annulus velocity < 8.5 cm/s and the early/late ratio < 1 could identify the pseudonormalization with a sensitivity of 88% and specificity of 67%. CONCLUSIONS: Mitral annulus velocity determined by DTI is a relatively preload-independent variable in evaluating diastolic function.

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

Force-frequency effect is a powerful determinant of myocardial contractility in the mouse.

The effects of heart rate (HR) on myocardial contractility in the mouse heart in situ were first investigated in open-chest mice (n = 7) by left ventricular (LV) catheter-tip micromanometry. HR was first slowed with a sinus node inhibitor (zatebradine), and atrial pacing to progressively increase the HR caused a positive inotropic response (assessed by maximum positive first derivative of LV pressure, LV dP/dtmax) up to a HR of 282 beats/min with the onset of a descending limb of the force-frequency relation (FFR) at 332 beats/min. beta-Adrenergic receptor stimulation (dobutamine) shifted upward and significantly steepened the positive FFR and increased HR at the onset of the descending limb to 402 beats/min. HR and LV dP/dtmax were then studied in closed-chest mice without pacing during recovery from anesthesia (n = 7), and during rest and intermittent physical activity the FFR was linear and positive up to 600 beats/min. HR was then progressively slowed with zatebradine, and the points at rest and during activity fell on the same linear relation. Thus we conclude the following: 1) in the open-chest anesthetized mouse, a positive FFR was amplified by beta-adrenergic receptor stimulation, and 20 in the mouse recovering from anesthesia the sinus node rate remained a critical determinant of myocardial contractility, without a descending limb of the FFR.

Anesthesia, General↗
PubMed1997

Temperature-guided radiofrequency catheter ablation of accessory pathway.

OBJECTIVES: This study was performed to evaluate the usefulness of temperature-guided radiofrequency catheter ablation for the elimination of accessory pathway conduction in patients with Wolff-Parkinson-White syndrome. METHODS: Temperature-guided radiofrequency catheter ablation was attempted in 138 patients with 144 accessory pathways (88 pathways along the left free wall, 5 in the anteroseptal region, 2 in the midseptal region, 19 in the posteroseptal region and 30 along the right free wall). The energy source was a HAT 200S which regulated the power automatically to the set temperature of 70 degrees C. Radiofrequency current was delivered through a thermocatheter to the atrial or ventricular side of mitral or tricuspid annulus. RESULTS: Accessory pathway conduction was eliminated in 130 of 144 pathways (90.3%). The mean power outputs of the successful ablations at the atrial side of the annulus were higher than those at the ventricular side (34.0 +/- 8.9W versus 20.0 +/- 7.6W, p < 0.01), but the maximum temperatures were lower at the atrial side of the annulus than those at the ventricular side (66.4 +/- 14.0 degrees C versus 77.2 +/- 6.4 degrees C, p < 0.01). There were 3 non-fatal complications (2.1%), 2 patients with hemopericardium and 1 with femoral artery thrombus, during or after ablation procedures. Recurrences of AV re-entrant tachycardia or delta wave on the electrocardiogram occurred in 4 patients (2.8%) who had successful second procedures. There were no late complications during a mean follow-up period of 41 +/- 25 months (range, 3 to 55). CONCLUSION: We conclude that 1) temperature-guided radiofrequency catheter ablation can be performed reliably and safely in eliminating accessory pathway conduction in patients with WPW syndrome, and 2) temperature monitoring and adjustment of the power to the set temperature during ablation would be useful for the avoidance of impedance rises and coagulum formation.

Adolescent↗
PubMed1996

Crystallization and preliminary x-ray crystallographic studies of ketosteroid isomerase from Pseudomonas putida biotype B.

The delta(5)-3-ketosteroid isomerase from Pseudomonas putida biotype B has been crystallized. The crystals belong to the space group P2(1)2(1)2(1) with unit cell dimensions of a = 36.48 angstrom, b = 74.30 angstrom, c = 96.02 angstrom, and contain one homodimer per asymmetric unit. Native diffraction data to 2.19 Angstrom resolution have been obtained from one crystal at room temperature indicating that the crystals are quite suitable for structure determination by multiple isomorphous replacement.

Crystallography, X-Ray↗
PubMed1995

Structure/function analysis of the periplasmic histidine-binding protein. Mutations decreasing ligand binding alter the properties of the conformational change and of the closed form.

The periplasmic histidine-binding protein, HisJ, is a receptor for the histidine permease of Salmonella typhimurium. Receptors of this type are composed of two lobes that are far apart in the unliganded structure (open conformation) and drawn close together in the liganded structure (closed conformation). The binding of the ligand, in a cleft between the lobes, stabilizes the closed conformation. Such receptors have several functions in transport: interaction with the membrane-bound complex, transmission of a transmembrane signal to hydrolyze ATP, and receiving a signal to open the lobes and release the ligand. In this study the mechanism of action of HisJ was further investigated using mutant proteins defective in ligand binding activity and closed form-specific monoclonal antibodies (Wolf, A., Shaw, E. W., Nikaido, K., and Ames G. F.-L. (1994) J. Biol. Chem. 269, 23051-23058). Y14H is defective in stabilization of the closed form, does not assume the closed empty form, and assumes an altered closed liganded form. T121A and G119R are similar to Y14H, but assume a normal closed liganded form. S72P binds the ligand to the open form, but does not assume a recognizable closed form. S92F is defective in the ability to undergo conformational change and to stabilize the closed form. All other mutant proteins appear to fall within one of these four categories. The biochemical characterization of these mutant proteins agrees with the structural analysis of the protein. We suggest that mutant proteins that do not assume the normal closed form, in addition to their defect in ligand binding, fail to interact with the membrane-bound complex and/or to transmit transmembrane signals.

Antibodies, Bacterial↗
PubMed1995

A probe molecule composed of seventeen percent of total diffracting matter gives correct solutions in molecular replacement.

It is often found in the crystallization of enzyme-inhibitor complexes that an inhibitor causes crystal packing which is different to that of native protein. This is the case for crystals of human non-pancreatic secreted phospholipase A(2) (124 residues) containing six molecules in the asymmetric unit when the protein is complexed with a potential acylamino analogue of a phospholid. The hexameric structure was determined by molecular replacement using the structure of monomeric native protein as a probe. As an extension to the experiment, it was tested whether a backbone polypeptide composed of 17% of a known monomeric structure could find its correct position on a target molecule in molecular replacement. A probe model composed of the backbone atoms of the N-terminal 77 residues of lysine-, arginine-, ornithine-binding protein (LAO, a total of 238 residues) liganded with lysine correctly finds its position on LAO liganded with histidine which crystallizes as a monomer in the asymmetric unit. The results indicate that as little as 17% of total diffracting matter can be used in molecular replacement to solve crystal structures or to obtain phase information which can be combined with phases obtained by the isomorphous-replacement method.

Journal Article↗
PubMed1995

Protein expression, selective isotopic labeling, and analysis of hyperfine-shifted NMR signals of Anabaena 7120 vegetative [2Fe-2S]ferredoxin.

Two alternative T7 RNA promoter/polymerase systems have been employed for the heterologous expression of a plant-type [2Fe-2S]ferredoxin, Anabaena 7120 vegetative ferredoxin, in Escherichia coli at high levels (approximately 20 mg/liter of culture). One system was used when 15N-labeling the ferredoxin uniformly by growing E. coli with 15NH4Cl as the nitrogen source; the other was used in conjunction with auxotrophic host strains to enrich the protein selectively by incorporating 2H-, 13C-, and 15N-labeled amino acids. The labeled ferredoxin samples were studied by 1H, 2H, 13C, and 15N NMR spectroscopy. Results from 1H and 2H NMR studies of samples containing [2H alpha]Cys, [2H beta 2, beta 3]Cys, [13 C beta]-Cys, and [15N]Cys have confirmed previous cysteinyl proton resonance assignments (L. Skjeldal, W. M. Westler, B.-H. Oh, A. M. Krezel, H. M. Holden, B. L. Jacobson, I. Rayment, and J. L. Markley (1991) Biochemistry 30, 7363-7368). All four 13C NMR peaks arising from the four cysteinyl beta-carbons and all four 15N NMR peaks from the four cysteinyl nitrogens were resolved in spectra of both the oxidized and reduced ferredoxins. The nitrogen resonance of Cys46, which is located in a unique (Ala-Cys) dipeptide, was assigned by detection of 13Ci-15Ni+1 coupling in a ferredoxin sample with incorporated [13C']Ala and [15N]Cys. The nitrogen signal of Cys 41 was assigned tentatively on the basis of its chemical shift and T1 relaxation time. The cysteinyl beta-carbon resonances in the reduced state have been assigned to individual residues on the basis of correlations with their (previously assigned) beta-protons. The beta-carbons resonance from Cys46 in the oxidized state has been assigned by its correlation with the corresponding resonance in the reduced state; this was accomplished by following the progressive air oxidation of a protein sample reduced by dithionite in the presence of methyl viologen. The spin-lattice relaxation times of the beta-carbons of the two cysteines coordinated to Fe)III) were similar in the oxidized and reduced states. This suggests that the antiferromagnetic coupling present in the reduced cluster has little influence on the electronic relaxation time of the Fe(III). Studies of the temperature dependence of the 1H, 13C, and 15N signals of the cysteinyl ligands to the [2Fe-2S] cluster show that the slope of the temperature dependence (delta delta/delta T-1) can be different for different atom types within a given residue. For example, in the reduced ferredoxin, although delta delta/delta T-1 is positive for Cys49 1H beta 2 and 1H beta 3, it is negative for Cys49 13C beta. Although delta delta/delta T-1 is negative for protons of cysteines ligated to Fe(II) and positive for protons of cysteines ligated to Fe(III), it is positive for all the cysteinyl nitrogens.(ABSTRACT TRUNCATED AT 400 WORDS)

Anabaena↗
PubMed1995

Evolution of left atrial thrombus with anticoagulant therapy-follow-up by transesophageal echocardiography.

OBJECTIVES: Atrial fibrillation is an important risk factor for systemic embolism. A number of clinical studies demonstrated the beneficial effect of anticoagulant therapy for the prevention of embolism. But there has been no study on the fate of left atrial thrombus demonstrated by transesophageal echocardiography in the course of anticoagulation therapy. METHODS: Thirteen patients, demonstrated to have left atrial thrombus by transesophageal echocardiography were followed with anticoagulation therapy. Repeated transesophageal echocardiography was done 15 months after 1st study. RESULTS: Among 9 patients with adequate anticoagulation effect (INR > 2.0), left atrial thrombus disappeared in 3 patients. The size of thrombus decreased from 2.2 +/- 0.8cm to 0.9 +/- 1.0cm (p < 0.05 by paired Student's t-test). CONCLUSIONS: Left atrial thrombus could dissolve or decrease in size with adequate anticoagulation.

Coronary Thrombosis↗
PubMed1994

Structural basis for multiple ligand specificity of the periplasmic lysine-, arginine-, ornithine-binding protein.

The substrate-binding site of a protein with multiple specificity should satisfy geometric and energetic complementarity for several different substrates. The structural basis of the multiple ligand specificity of the periplasmic lysine-, arginine-, ornithine-binding protein (LAO) was investigated by determining and analyzing the structures of the protein unliganded and liganded with each of the three high-affinity ligands (L-lysine, L-arginine, and L-ornithine) and with one low-affinity ligand (L-histidine). The geometric complementarity is achieved primarily by virtue of the large size of the ligand-binding site which can accommodate the maximum common volume of the four ligands plus three water molecules. The optimization of energetic complementarity is achieved by the relocation of protein-bound water molecules and by the movement of the Asp-11 side chain. The structure of the LAO-histidine complex indicates that the 30-fold reduced affinity of the protein for histidine is primarily due to unavailability of one ionic interaction of the histidine side chain with the protein which is present in the other three complexes.

Arginine↗
PubMed1994

The bacterial periplasmic histidine-binding protein. structure/function analysis of the ligand-binding site and comparison with related proteins.

Bacterial periplasmic binding proteins are initial receptors in the process of active transport across cell membranes and/or chemotaxis. Among them, the histidine-binding protein (HisJ) has been extensively studied from the biochemical, physiological, and genetic points of view. The three-dimensional crystal structure of the histidine-binding protein complexed with histidine has been determined at 2.5-A resolution by the molecular replacement method using a probe structure the previously solved lysine-liganded structure of the lysine-, arginine-, ornithine-binding protein (LAO), which shares 70% sequence identity with HisJ. The structure is bi-lobate; the two lobes, one bigger than the other, are connected by two short strands and are in contact with each other (closed) enclosing the histidine. Charged, polar, and non-polar side chains, as well as the peptide backbone, are involved in tight binding of the histidine. The bound histidine is involved in eight direct hydrogen bonds, six with the bigger lobe and two with the smaller lobe, in one potential water-mediated hydrogen bond with the bigger lobe, as well as in ionic interactions. The HisJ residues surrounding the ligand are the same as the LAO residues interacting with lysine, except for residue 52 which is leucine in HisJ and phenylalanine in LAO. The Leu-52 in HisJ makes a hydrophobic interaction with the imidazole ring of histidine. Of seven mutations affecting the ligand-binding site, five are located in the ligand-binding site, one in a connecting strand, and one at the domains interface. Based on comparisons among related binding proteins, the specific interactions between the ligands and the respective binding protein residues are predicted for the glutamine-binding protein and the opines-binding protein.

Bacterial Proteins↗
PubMed1994

Structure-function studies of [2Fe-2S] ferredoxins.

The ability to overexpress [2Fe-2S] ferredoxins in Escherichia coli has opened up exciting research opportunities. High-resolution x-ray structures have been determined for the wild-type ferredoxins produced by the vegatative and heterocyst forms of Anabaena strain 7120 (in their oxidized states), and these have been compared to structural information derived from multidimensional, multinuclear NMR spectroscopy. The electron delocalization in in these proteins in their oxidized and reduced states has been studied by 1H, 2H, 13C, and 15N NMR spectroscopy. Site-directed mutagenesis has been used to prepare variants of these ferredoxins. Mutants (over 50) of the vegetative ferredoxin have been designed to explore questions about cluster assembly and stabilization and to determine which residues are important for recognition and electron transfer to the redox partner Anabaena ferredoxin reductase. The results have shown that serine can replace cysteine at each of the four cluster attachment sites and still support cluster assembly. Electron transfer has been demonstrated with three of the four mutants. Although these mutants are less stable than the wild-type ferredoxin, it has been possible to determine the x-ray structure of one (C49S) and to characterize all four by EPR and NMR. Mutagenesis has identified residues 65 and 94 of the vegetative ferredoxin as crucial to interaction with the reductase. Three-dimensional models have been obtained by x-ray diffraction analysis for several additional mutants: T48S, A50V, E94K (four orders of magnitude less active than wild type in functional assays), and A43S/A45S/T48S/A50N (quadruple mutant).

Amino Acid Sequence↗
PubMed1994

Pulmonary artery aneurysm associated with hereditary hemorrhagic telangiectasia.

A patient with typical features of hereditary hemorrhagic telangiectasia was found to have massive dilatation and tortuosity of the main, right and left pulmonary artery with pulmonary hypertension. Pulmonary artery aneurysm with pulmonary hypertension has not been previously noted in patients with hereditary hemorrhagic telangiectasia. We report a 64-year-old woman showing this feature.

Aneurysm↗
PubMed1993

Three-dimensional structures of the periplasmic lysine/arginine/ornithine-binding protein with and without a ligand.

Many proteins exhibit a large-scale movement of rigid globular domains. Among these, bacterial periplasmic binding proteins involved in substrate transport, or transport and chemotaxis, can be used as prototypes for understanding the mechanism of the movement. Such movements have been found to be associated with specific functions, such as substrate binding, catalysis, and recognition by other biomolecules. We have determined the three-dimensional structures of the lysine/arginine/ornithine-binding protein (LAO) from Salmonella typhimurium with and without lysine by x-ray crystallographic methods at 1.8- and 1.9-A resolution, respectively. The structures are composed of two lobes held together by two short connecting strands. The two lobes are far apart in the unliganded structure, but in contact with each other in the lysine-liganded structure. The large movement of the lobes is a consequence of a 52 degrees rotation of a single backbone torsion angle in the first connecting strand and of distributed smaller changes of three backbone torsion angles of the second connecting strand. The absence of contact between the lysine and the connecting strands suggests that the ligand does not induce the conformational change directly. We instead propose that the unliganded protein undergoes a dynamic change between an "open" and a "closed" conformation and that the role of the ligand is to stabilize the closed conformation. We discuss the nature of a surface area which might be recognized by the membrane-bound complex of these amino acids transport systems.

Amino Acid Sequence↗
PubMed1993

Relation of pulmonary venous flow to mean left atrial pressure in mitral stenosis with sinus rhythm.

To determine whether pulmonary venous flow measured by transesophageal Doppler echocardiography can be used to estimate mean left atrial pressure (LAP), we prospectively studied 12 consecutive patients with sinus rhythm undergoing percutaneous mitral balloon commissurotomy for their severe mitral stenosis (mitral valve area < 1.5 cm2). We correlated Doppler variables of pulmonary venous flow and the mean LAP measured by left atrial catheterization. Among the variables of the pulmonary venous flow, the systolic fraction (i.e., the systolic velocity-time integral expressed as a fraction of the sum of systolic and early diastolic velocity-time integral) correlated significantly with mean LAP (r = -0.71, p < 0.05) and mitral valve area (r = 0.64, p < 0.05). Peak velocity and velocity-time integral in systole also significantly correlated with mean LAP (r = -0.66, r = -0.67 respectively, p < 0.05). We conclude that the more severe the degree of mitral stenosis in patients with sinus rhythm, the less systolic pulmonary venous flow in severe mitral stenosis.

Adult↗
PubMed1993

Coronary vasospasm, multiple coronary thrombosis, unstable angina and essential thrombocytosis.

Rarely, essential thrombocythemia has led to coronary artery occlusion. Only one patient has been described, in whom coronary angiography demonstrated multiple coronary thrombosis. We report a case of coronary vasospasm, multiple coronary thrombosis involving right and left coronary artery and possibly leading to myocardial infarction and unstable angina pectoris in a woman with migraine, Raynaud's phenomenon, and essential thrombocytosis.

Angina, Unstable↗