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Biomedical subjects

K C Cho

Publications and source records attributed to K C Cho.

At least 55 records · Page 3Linked to original sources
PubMed1985

Ultrasonic absorption in myoglobin and other globular proteins.

The ultrasonic absorption of myoglobin has been measured by the resonance and pulse-echo techniques as a function of pH. The absorption at a given frequency can be separated into pH-dependent and pH-independent contributions. Like other proteins, two peaks at pH 3 and 11.5 are observed which can be accounted for a proton-transfer reactions of the side-groups. In addition, the absorption undergoes a large increase within a small range of 0.2 pH unit at pH around 4, when denaturation of myoglobin occurs, indicating that the absorption is sensitive to the overall protein conformation. To elucidate the origin of the pH-independent component, the absorptions of several other globular proteins at neutral pH are also measured. The absorptions of these proteins exhibit a linear correlation with their isothermal compressibilities, suggesting that the pH-independent component is related to volume fluctuations of protein molecules. The activation energy of 4 kcal/mol found for this relaxation is consistent with such an interpretation.

Chymotrypsinogen↗
PubMed1985

Giant vascular malformation of the kidney: computed tomographic and angiographic appearances.

Two cases of giant vascular malformation of the kidney demonstrated by computed tomography and angiography are presented. The vascular malformations form completely outside the kidney. They arise from the renal parenchyma, simulating renal cyst, and present as a renal pelvic mass causing hydronephrosis. The finding of a renal mass with a markedly and uniformly contrast enhancement demonstrated by computed tomography should suggest the possibility of a vascular malformation.

Aged↗
PubMed1985

Abdominal tuberculosis: CT evaluation.

The computed tomography (CT) scans of 27 patients with abdominal tuberculosis were reviewed retrospectively to determine the range of abdominal involvement. Most patients had been at increased risk because of intravenous drug abuse, alcoholism, acquired immunodeficiency syndrome (AIDS), cirrhosis, or steroid therapy. The etiologic agent was Mycobacterium tuberculosis in 23 patients and M. avium-intracellulare in four patients with AIDS. In five patients, tuberculosis was limited to the abdomen. CT findings included adenopathy, splenomegaly, hepatomegaly, ascites, bowel involvement, pleural effusion, intrasplenic masses, and intrahepatic masses. Characteristic features were a tendency for adenopathy to prominently involve peripancreatic and mesenteric compartments, low-density centers within enlarged nodes, complex nature of the ascites, and adenopathy adjacent to sites of gastrointestinal tract involvement. Recognition of these manifestations and maintenance of an index of suspicion, especially in patients at risk, should help optimize the correct diagnosis and management of intraabdominal tuberculosis.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Computed tomography of Krukenberg tumors.

Computed tomography (CT) of three patients with Krukenberg tumor was reviewed retrospectively. CT showed large, lobulated, multicystic masses with soft-tissue components, indistinguishable from primary ovarian carcinoma. Indeed, CT and sonography of all three patients were initially interpreted as primary ovarian carcinoma. The ovary is a frequent site of metastases, particularly from colon carcinoma. These can be quite large, yet diagnosis is seldom made preoperatively. Much has been written about metastatic ovarian tumor, but this is the first report in the radiologic literature about their CT features. The authors emphasize the importance of recognizing the ovary as a frequent site of metastases and the proper approach to this problem. In patients with a history of colon or gastric carcinoma, the mixed cystic and solid ovarian mass on CT should be regarded as metastatic tumor until proven otherwise. A careful search for gastrointestinal tract signs or symptoms should be done in any patient with a pelvic tumor. When CT is done for evaluation of ovarian tumor, the stomach and colon should be carefully evaluated, and the ovaries routinely examined in the preoperative CT staging of gastric or colon carcinoma.

Aged↗
PubMed1985

Bile duct carcinoma in an adolescent.

Bile duct carcinoma is a relatively uncommon lesion that usually presents in the 6th to 7th decade. The only prior reported cases under the age of 20 were two patients with diseases known to predispose to the development of this tumor. We report a case of a 17-year-old girl with a bile duct tumor without any known predisposing factors.

Adenocarcinoma↗
PubMed1984

Kinetics of cold-induced denaturation of metmyoglobin.

Using a slow temperature-jump spectrophotometer, we have studied the kinetics of cold-induced denaturation of metmyoglobin between 0 degrees C and 20 degrees C at acidic pH. The time-scale of the transition is slow and is of the order of minutes. The results are consistent with the transition's involving a total of three states, native (N), transient intermediate (I) and denatured (D), which are converted from one to the other in that order.

Animals↗
PubMed1984

NMR spectroscopic identification of a hexacyanochromate(III) binding site on Pseudomonas azurin.

Studies of redox reactions between the blue copper protein azurin and inorganic reagents have suggested the formation of discrete complexes between the reaction partners prior to the actual electron-transfer step. To get an insight into the structural nature of the complexes formed, we have studied the interaction (i) between oxidized Pseudomonas aeruginosa azurin and the anion Fe(CN)6(3-) and (ii) between reduced azurin and Cr(CN)6(3-). At low ionic strengths, stoichiometric binding of one Fe(CN)6(3-) ion to the oxidized protein is observed. In the high-resolution proton magnetic resonance spectra of the reduced protein, specific broadening of the assigned residues is observed upon titration with the redox-inert Cr(CN)6(3-) ion. Analysis of this paramagnetic spectral broadening in terms of the three-dimensional structure of the protein has led to the proposal that the binding site of the anions lies approximately midway between lysine residues 85 and 92. Evidence in support of this conclusion is provided by parallel studies on Alcaligenes faecalis azurin, which lacks these lysine residues. A similar site on the surface of Pseudomonas azurin has recently been identified by affinity labeling with chromous ions as an electron-transfer locus [ Farver , O., & Pecht , I. (1981) Isr . J. Chem. 21, 13-17]. The results presented here suggest that this region on the protein surface also may be employed by anionic electron-transfer agents.

Alcaligenes↗
PubMed1983

An unusual pedunculated polyp of the colon: association with schistosomiasis.

A patient with long-standing, nonspecific abdominal symptoms had a barium enema showing a single pedunculated polyp. This was removed by colonoscopic polypectomy and found to be an inflammatory polyp associated with Schistosoma mansoni infection. We review the relationship and significance of schistosomiasis to colonic polyps.

Barium Sulfate↗
PubMed1982

The thermodynamics of myoglobin stability. Effects of axial ligand.

The reversible thermal denaturation of four metmyoglobin derivatives, aquomet, cyanomet, azidomet and fluoromet in both the alkaline pH and acidic pH region, has been examined by optical spectrophotometry. The data are analyzed in terms of a two-state model to extract the thermodynamic parameters delta G, delta H, delta S and delta Cp characterizing the transition. The results are consistent with Brandts' phenomenological model of protein denaturation. Among the derivatives examined, cyanomet, azidomet and fluoromet are about 3 kcal/mol, 2 kcal/mol and 0.2 kcal/mol, respectively, more stable than aquometmyoglobin. The observed differences are found to be inconsistent with the hypothesis that the stability is mainly governed by the spin state of the iron atom. In addition, the enthalpic and entropic contributions in delta G are extracted and the differences in delta G for the various derivatives are found to arise from minor changes in delta H and T delta S. Assuming the final denaturated state to be universal, these changes reflect the effect of ligands on the conformational energy of the native protein.

Fluorides↗
PubMed1982

A calorimetric study of the thermal transitions of Halobacterium cutirubrum.

The thermal transitions of Halobacterium cutirubrum have been examined by differential scanning calorimetry. Two distinct peaks corresponding to the denaturation of two major protein components were observed in the heating curves. One of the peaks has been assigned to the denaturation of the envelope glycoprotein. The variations of the denaturation temperatures with the addition of glucose, glycerol, NaNO3, and NaSCN are consistent with the previous proposal that hydrophobic interactions are essential in stabilizing the glycoprotein.

Calorimetry, Differential Scanning↗
PubMed1981

Resonance Raman studies of methemoglobin derivatives at room temperature and 77 K.

Raman spectra in preresonance with the Soret absorption band are reported for the following methemoglobin derivatives: cyanide, cyanate, thiocyanate, hydroxy-, azide, and fluoride methemoglobin at 285 K and 77 K. For the mixed-spin derivatives, Raman intensity is observed to shift from the high-spin marker band (approx. 1480 cm-1) to the low-spin marker band (approx. 1505 cm-1) upon cooling to 77 K. In addition, Raman spectra of cyanate methemoglobin were taken as a function of temperature, and the log of the intensity ratio I1480/I1505 was found to be a linear function of 1/T, indicating a thermally activated process. We interpret these results as observations of temperature-induced spin transitions. In the case of cyanate methemoglobin we find the enthalpy and entropy differences between the high-spin and low-spin states to be deltaH = 600 +/- 40 cal x mol-1 and deltaS = 4.7 +/- 0.7 cal x mol-1 x K-1. The high-spin to low-spin ratio for cyanate methemoglobin determined by our experiment disagrees with the value reported for magnetic susceptibility measurements.

Humans↗
PubMed1981

Kinetics of the pretransition of synthetic phospholipids. A calorimetric study.

The pretransition in aqueous dispersions of two synthetic phospholipids (dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine) has been examined in detail by differential scanning calorimetry. The transition from the high-temperature state (state above pretransition) to the low-temperature state (state below pretransition) is complex and appears to occur via some metastable states. In contrast, the kinetics of the transition from the low- to the high-temperature state is consistent with an activated two-state model. The observed hysteresis is shown to arise mainly from the kinetic nature of the pretransition.

Calorimetry, Differential Scanning↗
PubMed1980

Thermal stability of hemoglobin and myoglobin: effect of spin states.

The thermal stability of various methemoglobin and metmyoglobin derivatives at different ligand concentrations and pH were studied by the method of differential scanning calorimetry. Comparing to water as a ligand, cyanide and azide are most effective in protecting the protein; fluoride stabilizes the protein slightly whereas imidazole and thiocyanate have little effect. Assuming thermal denaturation can be described by an activated two-state process, the activation parameters of all the derivatives were determined. We have also found that the stability of hemoglobin and myoglobin does not correlate with the iron atom spin state but depends instead on steric interactions with the ligands. On the reasonable assumption that structure and stability are related, this implies a definite dependence of structure on steric interactions.

Calorimetry, Differential Scanning↗
PubMed1979

Spin equilibrium and quaternary structure change in hemoglobin A. Experiments on a quantitative probe of the stereochemical mechanism of hemoglobin cooperativity.

The molecular mechanism of hemoglobin cooperativity was studied kinetically by flash photolysis on mixed-state hemoglobins which consist of three ferrous carboxy subunits and one hybrid ferric subunit including fluoromet, azidomet, cyanatomet, and thiocyanatomet. The effects of conformational transitions on the hybrid subunit were detected by kinetic absorption spectroscopy after the CO was fully photodissociated from the binding sites by a large pulse of light from a tunable dye laser. The hemoglobin conformational transition rate was observed to depend on its state of ligation. At 22 degrees C, pH 7, and 0.1 M phosphate, the deoxy R yields T conformational change rate is 4 x 10(4)s-1. The rate decreases to 1.4 x 10(4)s-1 for singly ligated hemoglobin. The R yields T conformation change alters the energy separation between high- and low-spin states for azidomet, cyanatomet, and thiocyanatomet subunits by about 700, 300, and 300 cal/mol, respectively. There are two possible implications of this result: (1) the iron atom spin state is not the only major factor in the determination of its position with respect to the heme plane or (2) the change with conformation of the protein force exerted by the proximal histidine on the iron atom (for an iron to heme-plane displacement of less than 0.3 A) is less than 50% of that expected from simple models in which this motion is responsible for cooperativity.

Azides↗