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Biomedical subjects

C Ho

Publications and source records attributed to C Ho.

At least 199 records · Page 11Linked to original sources
PubMed1989

Effects of cholesterol or gramicidin on slow and fast motions of phospholipids in oriented bilayers.

Nuclear spin-lattice relaxation both in the rotating frame and in the laboratory frame is used to investigate the slow and fast molecular motions of phospholipids in oriented bilayers in the liquid crystalline phase. The bilayers are prepared from a perdeuterated phospholipid labeled with a pair of 19F atoms at the 7 position of the 2-sn acyl chain. Phospholipid-cholesterol or phospholipid-gramicidin interactions are characterized by measuring the relaxation rates as a function of the bilayer orientation, the locking field, and the temperature. Our studies show that cholesterol or gramicidin can specifically enhance the relaxation due to slow motions in phospholipid bilayers with correlation times tau s longer than 10(-8) sec. The perturbations of the geometry of the slow motions induced by cholesterol are qualitatively different from those induced by gramicidin. In contrast, the presence of cholesterol or gramicidin slightly suppresses the fast motions with correlation times tau f = 10(-9) to 10(-10) sec without significantly affecting their geometry. Weak locking-field and temperature dependences are observed for both pure lipid bilayers and bilayers containing either cholesterol or gramicidin, suggesting that the motions of phospholipid acyl chains may have dispersed correlation times.

Cholesterol↗
PubMed1989

Relationship between Fungal Biomass Production and the Brightening of Hardwood Kraft Pulp by Coriolus versicolor.

The white-rot fungus Coriolus versicolor increased the brightness of hardwood kraft pulp by two mechanisms depending on the concentration of available nitrogen. In low-nitrogen conditions, the brightening process was a chemical effect mediated by the fungus, associated with the removal of residual lignin in the pulp; kappa number was used as an indicator of lignin concentration. A five-day treatment in low-nitrogen conditions increased the brightness of hardwood kraft pulp from 36.2 to 54.5%, with a corresponding decrease in kappa number from 12.0 to 8.5, equivalent to a reduction in the lignin concentration from ca. 2.0% (wt/wt) to ca. 1.4% (wt/wt). Under these conditions, we concluded that the brightening of the pulp was a secondary metabolic event initiated after the depletion of available nitrogen. This method of brightening has been described as bleaching or biobleaching. By contrast, in high-nitrogen conditions, the brightening was a physical effect associated with the dilution of the dark pulp fibers by the relatively high levels of brighter fungal mycelium produced. Since this method of brightening was not evidently associated with lignin removal, it cannot be described as bleaching. In pulp samples brightened in high-nitrogen conditions, as brightness increased, there was a corresponding increase in kappa number. This observation was explained by the consumption of potassium permanganate by the fungal mycelium, which interfered with kappa number determinations at high fungal biomass levels.

Journal Article↗
PubMed1989

Diagnostic imaging of lower extremity trauma.

Traumatic injuries to the lower extremity are a common occurrence in today's society and may result in significant morbidity and mortality if not appropriately treated. Adequate radiographic evaluation is crucial to the assessment of these injuries. This article reviews the radiographic features and imaging approaches to the commonly encountered injuries of the lower extremity.

Femoral Fractures↗
PubMed1989

Conventional tomography in musculoskeletal trauma.

Conventional tomography utilizes controlled blurring of overlying structures, in effect, to remove these possible obscuring overlying structures and permit improved evaluation of anatomic detail within the specific layer or focal plane of interest. Although it has largely been replaced by true sectional imaging modalities such as CT and MR imaging, it remains a valuable tool in specific settings as in musculoskeletal trauma. It is particularly useful when the orientation of the pathology requires coronal or sagittal planes for optimal evaluation.

Arthrography↗
PubMed1988

31P NMR measurements of myocardial pH in vivo.

A 31P NMR magnetization transfer method for measuring myocardial pH in vivo is demonstrated in the lamb, dog and cat. The method involves measuring the difference in chemical shift between the resonances of phosphocreatine and inorganic phosphate in magnetization transfer difference spectra in which the gamma-phosphate resonance of ATP has been saturated. The method has been verified by measuring the chemical shift difference between the resonances of 2-deoxyglucose 6-phosphate and phosphocreatine following infusion of the animals with 2-deoxyglucose. The measured pH values are significantly lower than those obtained in previous studies on the heart in vivo.

Animals↗
PubMed1988

Rotating-frame relaxation studies of slow motions in fluorinated phospholipid model membranes.

Rotating-frame relaxation experiments have been carried out on 19F-labeled dimyristoylphosphatidylcholine model membranes. The lipids are labeled with a single CF2 group in the 4-, 8-, or 12-position of the 2-acyl chain. Both oriented lipid bilayers and multilamellar liposomes have been investigated. The relaxation rate has been measured as a function of the locking-field strength, the sample orientation, the label position, and the temperature. Our results have confirmed that extensive slow motions exist in the bilayer and dominate the low-frequency relaxation. The relaxation rate is quite sensitive to the label position. However, many other features of the relaxation are very similar for all three lipid isomers. The temperature dependence of the relaxation rate for the multilamellar liposomes differs from the oriented bilayers, which may imply that the motions are also different. To fit our data, a working model consisting of a superposition of an anisotropic reorientation term and a director fluctuation term has been proposed. We have also verified that almost all of the relaxation process is caused by modulations of the intramolecular interactions. Based on this, a view of the slow motions at a molecular level is discussed in this paper.

Dimyristoylphosphatidylcholine↗
PubMed1988

Determination of rat brain buffering in vivo by 31P-NMR.

Buffering capacity of most tissues is composed of both rapid and slow phases, the latter presumably due to active acid extrusion. To examine the time course of brain buffering the brain pH of Sprague-Dawley rats was measured using 31P-nuclear magnetic resonance. The effect on brain pH of 30- or 58-min exposures to 20% CO2 followed by 30- or 38-min recovery periods, respectively, was studied. Brain pH reached its lowest value after a 15-min exposure to elevated CO2, thereafter slowly and steadily increasing. During recovery brain pH rose rapidly in the first 5 min exceeding control brain pH by 0.08 pH units. Brain pH fell during the next 30 min despite increases in blood pH and decreases in blood CO2 tension. Calculated intrinsic brain buffering rose steadily threefold during the last 40 min of CO2 exposure and during the final 30 min of recovery. These data show that in rat brain there is a temporally late buffering process, most likely active acid extrusion, requiring greater than 30 min for full activation and at least 30 min for discontinuation.

Animals↗
PubMed1987

A proton nuclear Overhauser effect investigation of the subunit interfaces in human normal adult hemoglobin.

High-resolution proton nuclear magnetic resonance spectroscopy and nuclear Overhauser effects for the low-field exchangeable proton resonances of human normal adult hemoglobin in aqueous solvents are being used to confirm and extend the assignments of these resonances to specific protons at the intersubunit interfaces of the molecule. Most of these exchangeable proton resonances of human normal adult hemoglobin have been found to be absent in the spectra of isolated alpha or beta subunits. This finding indicates that they are specific spectral markers for the quaternary structure of the hemoglobin tetramer. Based on the nuclear Overhauser effect results, we have assigned the exchangeable proton resonance at +7.4 ppm downfield from H2O to the hydrogen-bonded proton between alpha 103(G10)His and beta 108(G10)Asn at the alpha 1 beta 1 interface. The nuclear Overhauser effect results have also confirmed the assignments of the exchangeable proton resonances at +9.4 and +8.2 ppm downfield from H2O previously proposed by workers in this laboratory based on a comparison of human normal adult hemoglobin and appropriate mutant hemoglobins. This independent confirmation of previously proposed assignments is necessary in view of the possible long-range conformational effects of single amino-acid substitutions in mutant hemoglobin molecules.

Adult↗
PubMed1987

Oxygen equilibrium studies of cross-linked asymmetrical cyanomet valency hybrid hemoglobins: models for partially oxygenated species.

Oxygen equilibrium curves have been measured to determine the binding constant at each oxygenation step (Ki) for various cross-linked hemoglobins, (alpha beta)A(alpha beta)CXL, (alpha +CN beta)A(alpha beta)CXL, (alpha beta +CN)A(alpha beta)CXL, (alpha +CN beta +CN)A(alpha beta)CXL, and (alpha beta +CN)A(alpha +CN beta)CXL, where the subscripts A and C denote that the alpha beta dimer is derived from human normal adult hemoglobin and mutant hemoglobin C (beta 6Glu----Lys), respectively, and XL denotes cross-linking between the lysyl residues at position 82 in the two beta chains by bis(3,5-dibromosalicyl) fumarate as described by Miura and Ho [Miura, S., & Ho, C. (1982) Biochemistry 21, 6280-6287]. The oxygen equilibrium data indicate that the oxygen affinity increases with the number of cyanomet hemes carried by the cross-linked mixed valency hybrid hemoglobins. The oxygen binding property depends not only on the number of the subunits carrying cyanomet hemes but also on the distribution of cyanomet hemes among the four subunits. A striking effect is observed in singly cyanomet valency hybrid hemoglobins; namely, (alpha +CN beta)A(alpha beta)CXL exhibits lower oxygen affinity and higher cooperativity than (alpha beta +CN)A(alpha beta)CXL. The magnitude of the Adair constants and their pH dependency of (alpha +CN beta)A(alpha beta)CXL (Ki, i = 1-3) are analogous to those of the Adair constants of (alpha beta)A(alpha beta)CXL (Ki, i = 2-4), whereas such an analogy is not observed between (alpha beta +CN)A(alpha beta)CXL and (alpha beta)A(alpha beta)CXL. The doubly cyanomet mixed valency hybrid cross-linked hemoglobins exhibit high oxygen affinity and reduced cooperativity, and their Adair constants are not analogous to K3 and K4 of (alpha beta)A(alpha beta)CXL.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemoglobins↗
PubMed1987

Nuclear magnetic resonance and molecular genetic studies of the membrane-bound D-lactate dehydrogenase of Escherichia coli.

In this study we demonstrate the potential of combining fluorine-19 nuclear magnetic resonance (NMR) spectroscopy with molecular genetics. We are using the membrane-bound enzyme D-lactate dehydrogenase of Escherichia coli as a model system to characterize interactions between proteins and lipids. We have labeled D-lactate dehydrogenase with 4-, 5-, and 6-fluorotryptophans and obtained high-resolution fluorine-19 NMR spectra showing five resonances, in agreement with the five tryptophan residues expected from the DNA sequence. The five 19F resonances in the spectra have been assigned to the specific tryptophan residues in the primary sequence of D-lactate dehydrogenase by site-directed oligonucleotide mutagenesis of the cloned gene. We observe large differences in the relative fluorine-19 chemical shifts of each tryptophan residue when labeled by different isomers of fluorotryptophan. We have determined by NMR methods that two tryptophans are exposed to the solvent and that none of the tryptophan residues are within 10 A of the lipid phase. On the basis of 19F NMR spectroscopy of the labeled tryptophan residues, the conformation of D-lactate dehydrogenase is similar in aqueous solution and in the presence of a variety of lipids and detergents. This result indicates that the presence of lipids or detergents is not required to maintain the tertiary structure of this membrane-bound enzyme. In contrast, Triton X-100 induces a change to an abnormal conformation of the enzyme as judged from both NMR spectroscopy and the effect of temperature on the maximal velocity of the enzyme in the presence of this detergent.

Cell Membrane↗
PubMed1987

Falsely elevated CSF total protein due to carryover in a discrete analyzer (Beckman Astra-8).

Falsely elevated values for CSF total protein, as determined in the Beckman Astra-8 Total Protein Module, were shown to be due to a combined effect of sample cross-contamination and reaction cup contamination by serum samples on the same sample tray. Normal CSF may be misdiagnosed as having an abnormally high protein concentration, due to this interference by normal serum samples. To avoid this carryover phenomenon, it is recommended that 3 saline samples be analysed for total protein before the analysis of the CSF samples; alternatively, all the CSF samples should be analysed separately in one batch.

Cerebrospinal Fluid Proteins↗
PubMed1987

Proton NMR studies of the molecular basis for the anti-sickling activity of non-covalent antisickling compounds.

Two new techniques of nuclear magnetic resonance spectroscopy are proposed to identify and characterize the binding sites of antisickling compounds to Hb S: measurements of the longitudinal relaxation rates (T1(-1)) of the C2 protons of individual surface histidyl residues of the C2 protons of individual surface histidyl residues of Hb S and intermolecular transferred nuclear Overhauser effects from protons in the heme pockets of the Hb S molecule. Using these methods, we have investigated the binding sites of L-phenylalanine, L-tryptophan, L-valine, and p-bromobenzylalcohol to sickle hemoglobin. With the exception of L-valine, all of these molecules are known to inhibit the polymerization of deoxy Hb S. We have found that for the compounds with antisickling activity, there are at least two binding sites to the Hb S molecule, one at or near the heme pockets of the alpha and beta chains and the other one in the vicinity of the beta 6 mutation site.

Antisickling Agents↗
PubMed1987

[Effect of the form of anesthesia (pentobarbital, Velonarcon/Faustan) on determination of the glomerular filtration rate in the rat model].

During the renal functional diagnostics at the narcotized rat in various forms of anaesthesia (Pentobarbital and Velonarcon/Faustan) the behaviour of the blood pressure was continuously registered. In contrast to the Velonarcon/Faustan anaesthesia, in which a distinct hypertonic reaction was observed which normalized itself only after 100 minutes with the Pentobarbital anaesthesia an approximately invariable constant blood pressure level lying in the renal autoregulative region could be achieved during the whole period of investigation.

Anesthetics↗
PubMed1986

Biochemical and morphological properties of membranes of unsaturated fatty acid auxotrophs of Salmonella typhimurium: effects of fluorinated myristic acids.

In order to investigate the utility of the fluorine-19 nucleus as a spectroscopic probe, a fluorinated analog of myristic acid has been incorporated into the membrane lipids of an unsaturated fatty acid auxotroph of Salmonella typhimurium. It is capable of supporting limited growth at temperatures above 37 degrees C. Freeze-fracture electron microscopic examinations of the membrane ultrastructure show a temperature and fatty acid supplement-dependent segregation of intramembranous protein particles into distinct patches in the auxotrophic membrane leaving intramembranous protein-denuded areas. The occurrence of these patches seems to be related to the phase separation of membrane lipids. Corresponding changes in the transport and accumulation of methyl thio-beta-D-galactopyranoside and tetracycline are observed. However, transport of histidine does not appear to be dependent on the physical state of the membrane lipids. The auxotroph shows differences in growth and morphological characteristics from those of the wild type. Functions of both inner and outer membranes are shown to be affected as a response to the fatty acid chain composition of the lipids.

Cell Membrane↗
PubMed1986

Assessment of role of beta 146-histidyl and other histidyl residues in the Bohr effect of human normal adult hemoglobin.

The contribution of the carboxyl-terminal histidines of the beta chains, beta 146(HC3), to the alkaline Bohr effect of human normal adult hemoglobin has been shown by this laboratory to depend upon the solvent composition. Using high-resolution proton nuclear magnetic resonance spectroscopy, we have found that the pKa value of the beta 146-histidine is 8.0 in the deoxy form, while in the carbonmonoxy form it ranges from 7.1 to 7.85 depending upon the concentration of inorganic phosphate and chloride ions present. These conclusions have been questioned by Perutz and co-workers on the basis of biochemical, structural, and proton nuclear magnetic resonance studies of mutant and enzymatically or chemically modified hemoglobins [Perutz, M. F., Kilmartin, J. V., Nishikura, K., Fogg, J. H., Butler, P. J., & Rollema, H. S. (1980) J. Mol. Biol. 138, 649-670; Kilmartin, J. V., Fogg, J. H., & Perutz, M. F. (1980) Biochemistry 19, 3189-3193; Perutz, M. F., Gronenborn, A. M., Clore, G. M., Fogg, J. H., & Shih, D. T.-b. (1985) J. Mol. Biol. 183, 491-498]. In this work, we use proton nuclear magnetic resonance spectroscopy to assess the effects of structural modifications on the histidyl residues and on the overall conformation of the hemoglobin molecule in solution. The structural perturbations investigated all occur within the tertiary domains around the carboxyl-terminal region of the beta chain as follows: Hb Cowtown (beta 146His----Leu); Hb Wood (beta 97His----Leu); Hb Malmö (beta 97His----Gln); Hb Abruzzo (beta 143His----Arg). Our results demonstrate that the conformational effects of single-site structural modifications upon the conformation and dynamics of hemoglobin depend strongly on their location in the three-dimensional structure of the protein molecule and also on their chemical nature. Furthermore, in normal hemoglobin, the spectral properties of several surface histidyl residues are found to depend, in the ligated state, upon the nature of the ligand. Our present findings do not support the recent spectral assignments proposed by Perutz et al. (1985) for the proton resonances of the beta 146- and beta 97-histidines and their suggestion that the enzymatic removal of the carboxyl-terminal beta 146-histidyl residues induces a conformational equilibrium for the beta 97-histidines in the des-beta 146His hemoglobin molecule in the carbonmonoxy form.

Hemoglobin A↗