Search PubMed⌕ Search

Biomedical subjects

J Jonas

Publications and source records attributed to J Jonas.

At least 37 records · Page 2Linked to original sources
PubMed1998

High-resolution, high-pressure NMR studies of proteins.

Advanced high-resolution NMR spectroscopy, including two-dimensional NMR techniques, combined with high pressure capability, represents a powerful new tool in the study of proteins. This contribution is organized in the following way. First, the specialized instrumentation needed for high-pressure NMR experiments is discussed, with specific emphasis on the design features and performance characteristics of a high-sensitivity, high-resolution, variable-temperature NMR probe operating at 500 MHz and at pressures of up to 500 MPa. An overview of several recent studies using 1D and 2D high-resolution, high-pressure NMR spectroscopy to investigate the pressure-induced reversible unfolding and pressure-assisted cold denaturation of lysozyme, ribonuclease A, and ubiquitin is presented. Specifically, the relationship between the residual secondary structure of pressure-assisted, cold-denatured states and the structure of early folding intermediates is discussed.

Biophysical Phenomena↗
PubMed1997

Structure of pressure-assisted cold denatured lysozyme and comparison with lysozyme folding intermediates.

At high (> 3.5 kbar) pressures and low (< -10 degrees C) temperatures, hen egg-white lysozyme denatures readily and reversibly. Amide hydrogen exchange methods were used to investigate the structure of the pressure-assisted cold-denatured state of lysozyme. Protection factors were obtained for 52 backbone amide protons. The extent of protection of many of these protons is markedly different from that in lysozyme denatured by high temperature, high urea concentration, or chemical modification; specifically, the protection factors are higher and are strongly correlated with elements of secondary structure present in the native state. Furthermore, the pattern of protection factors is similar to that observed in lysozyme during refolding from highly denatured states, particularly during the early stages (< 3.5 ms) of refolding [Gladwin, S. T., & Evans, P. A. (1996) Folding Des. 1, 407]. Previous data on cold-denatured ribonuclease A were reevaluated and compared to known folding intermediates [Houry, W. A. & Scheraga, H. A. (1996) Biochemistry 35, 11734; Udgaonkar, J. B., & Baldwin, R. L. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 8197] to further test the supposition that the pressure-assisted cold-denatured states of proteins resemble the early folding stages.

Animals↗
PubMed1997

Structure of the pressure-assisted cold denatured state of ubiquitin.

The pressure-assisted cold denatured state of ubiquitin in aqueous solution was investigated by high resolution NMR. Hydrogen exchange kinetics were measured for backbone amide protons in the cold denatured protein to determine its structure. In contrast to cold denatured ribonuclease A and lysozyme, cold denatured ubiquitin shows little persistent secondary structure. The behavior of ubiquitin supports the idea of a relationship between the residual structure of pressure-assisted cold-denatured states and the structure of early folding intermediates provided they exist.

Cold Temperature↗
PubMed1997

[Are there genuine and pseudo-normal pressure glaucomas? Body position-dependent intraocular pressure values in normal pressure glaucoma].

BACKGROUND: Elevation of intraocular pressure in the supine position has been previously described in literature. Aim of this study is to investigate the elevation of intraocular pressure in normal tension glaucoma and its effect on the morphology of the optic disc, visual field function and capillary blood flow of the retina and optic disc. PATIENTS AND METHODS: 56 eyes of 28 preperimetric and advanced normal tension glaucoma patients were prospectively evaluated. Ten eyes of ten normal patients served as a control group for the measurements of the intraocular pressure. In the course of a 24-h pressure profile applanation tonometry was performed in the morning in a supine and three and ten minutes later in a sitting position with Draeger's and Goldmann's tonometers. Arterial blood pressure was measured at the same time. The optic disc's morphology was evaluated by stereo photographs and Laser Scanning Tomography. As a sensory test computer perimetry was used. Capillary blood flow was measured at defined areas of the retina and optic disc. An intraocular pressure above 21 mm Hg in the supine position was used as a criterium to define two groups of normal tension glaucoma patients. RESULTS: In the supine position a statistically significant elevation of intraocular pressure was observed in 24 normal tension glaucoma patients by 6.2 +/- 2.8 mm Hg up to 21.8 +/- 3 mm Hg. Diastolic blood pressure in the supine position (80 +/- 10.5 mm Hg) was significantly lower than in the sitting position (94 +/- 11 mm Hg, p = 0.021). 12 of 28 normal tension glaucoma patients showed an intraocular pressure lower than 22 mm Hg in the supine position. In these patients a tendency towards a higher incidence for the occurrence of optic disc haemorrhages and significantly higher values for blood flow (p < 0.0005) and volume (p < 0.005) in the retina and optic nerve head could be shown. In this group of normal pressure glaucoma patients a higher incidence of migraine and vasospastic complaints was reported in the patients' history. CONCLUSION: In this study some normal tension glaucoma patients showed intraocular pressures in the supine position higher than 21 mm Hg and a lower diastolic arterial pressure. The higher incidence of haemorrhages and higher values for flow and volume parameters of the optic disc in normal tension glaucoma patients with an intraocular pressure lower than 22 mm Hg implicate the existence of two entities: real and pseudo normal tension glaucomas.

Adult↗
PubMed1997

Optic disk.

Explore the source record for details and available documents.

Adult↗
PubMed1996

Hydrogen-exchange kinetics in the cold denatured state of ribonuclease A.

Ribonuclease A (RNase A) exhibits a well-defined cold denaturation transition when examined at high pressure (3 kbar) and low temperatures (below -10 degrees C). Our main interest in this study was to investigate the pressure-assisted cold denatured state of RNase A by hydrogen exchange techniques. The protection factors obtained from the kinetic data are similar to those obtained previously for RNase A denatured by exposure to high pressure near its temperature of maximum stability, but differ markedly from those in thermally denatured RNase A. A qualitative analysis of the hydrogen-exchange rates suggests that cold denatured RNase A behaves markedly differently from a random coil, probably due to patches of residual secondary structure.

Amides↗
PubMed1996

High-Resolution NMR Probe for Experiments at High Pressures

A 300 MHz high-resolution, high-pressure NMR probe which operates in the pressure range of 1 bar to 9 kbar at temperatures of -30 to 100&deg;C is described. Specialized novel design features of the probe are discussed and test spectra showing resolution better than 1 Hz (<3.0 x 10(-9)) for 8 mm samples are presented. Potential biochemical applications of this probe are illustrated by experiments dealing with the pressure-induced unfolding of hen egg white lysozyme.

Journal Article↗
PubMed1996

[Reperfusion shock after occlusion of the superior mesenteric artery and accumulation of leukocytes within the wall of the small intestine].

The epithelial damage and the accumulation of the leucocytes within intestinal wall layers after ischemia and reperfusion was investigated in a pig model. Superior mesenteric artery (SMA) was occluded for 1 h (group 2, n = 9), 2 h (group 3, n = 6) and 3 h (group 4, n = 7) with a consecutive 2 h reperfusion period. The histological evaluation was performed on hematoxylin-eosine and Naphtol AS-D chloracetate stained preparations. The intensity of reperfusion shock depended on the duration of the intestinal ischemia. After 1 h SMA occlusion systolic blood pressure stabilized at a lower level with a normalization of the serum lactate level and the intestinal intramural pHi within the reperfusion period. After 2 h SMA occlusion the decrease of the systolic blood pressure was intensified (54-69 mm Hg) with a persistent elevated serum lactate concentration and a delayed increase of the ischemic pHi values. Reperfusion after 3 h SMA occlusion caused an irreversible shock. The epithelial damage also depended on the duration of the SMA occlusion. There were no significant changes of the leucocytic accumulation within the submucosa. But a significant increase of the number of the leucocytes was seen within the inner and the outer layer of the muscularis after 1 h SMA occlusion (106+/-5/mm2 resp. 280/mm2; p<0.05). This increase was less pronounced after 2 h (92+/-5/mm2*resp. 189+/-4/mm2; *p<0.05) and 3 h of SMA occlusion (84+/-5/mm2 resp. 185+/-23/mm2). Intestinal ischemia and reperfusion caused no changes of the leucocytic accumulation within the submucosa but a significantly increased accumulation within the muscularis after 1 h SMA occlusion, which was not seen after a more elongated occlusion period. A reperfusion shock without normalization of the serum lactate level and the intramural pHi suggesting intestinal perfusion disturbances may also lead to a depression of the leucocytic accumulation within the muscularis.

Animals↗
PubMed1996

[Behavior of the lactate level in occlusion and reperfusion of the right superior mesenteric artery. An animal experiment study].

The value of lactate in the early clinical diagnosis of acute mesenteric arterial occlusion was evaluated in an animal model. The superior mesenteric artery of pigs (8-9 weeks old, 20-23 kg) was clamped for 1 h (group 2, n = 9) and 3 h (group 3, n = 6). Reperfusion was recorded for 2 h. Follow-up measurements were done in six animals (group 1). The systolic blood pressure was elevated significantly to about 18-40 mmHg in the initial phase of ischemia (P = 0.02). The intramucosal pHi measured tonometrically was decreased to below a value of 7.08 (P = 0.03), and the flow of superior mesenteric vein was reduced by about 90% ( P = 0.03) in groups 2 and 3. Within 30 min the lactate increased to about 2.05-3.8 mmol/l in the central venous blood sample and 2.8-4.8 mmol/l in the portal vein blood sample in 30 min. After 3 h of ischemia (group 3) the elevated lactate level returned to normal without any significant difference. In the reperfusion period (group 2) the systolic blood pressure stabilized at a depressed level (63-73 mmHg, P = 0.0054), and the flow of the superior mesenteric vein showed a reduction of 41% (P = 0.03). Intramucosal pHi and lactate values returned nearly completely to normal within 2 h. Reperfusion after 3 h of ischemia (group 3) caused marked shock without any sign of recovery at intramucosal pH or mesenteric vein flow. The lactate values increased for above the ischemic level. In conclusion, an elevated lactate level only correlates with the initial phase of acute mesenteric arterial occlusion. A normal lactate concentration cannot exclude the diagnosis of mesenteric ischemia. Reperfusion of the ischemic intestine is characterized by circulatory shock with secondary increased lactate concentration without predictive value for adequate intestinal perfusion.

Animals↗
PubMed1995

High-pressure proton NMR study of lateral self-diffusion of phosphatidylcholines in sonicated unilamellar vesicles.

Effects of pressure on the lateral diffusion of phospholipid molecules in sonicated pure 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) vesicles (15 wt%) in D2O were examined using the high-pressure proton NMR rotating frame spin-lattice relaxation time (T1rho) method. Proton T1rho were measured at pressures from 1 bar to 5000 bar and at temperatures of 50 degrees C to 70 degrees C for DPPC and 5 degrees C to 35 degrees C for POPC. The T(-1)1rho values were plotted as a function of the square root of the spin-locking field angular frequency (omega1(1/2) and the lateral diffusion coefficient (D) calculated from the slope. Pressure effects on lateral diffusion were observed in the liquid-crystalline (LC) phase. The lateral diffusion coefficient exhibited sharp decreases in response to the various pressure-induced phase transitions encountered. However, pressure had little, if any, effect on lateral diffusion in the pressure-induced gel I (GI) phase and pressure-induced interdigitated gel (Gi) phase. The activation volumes for diffusion were calculated from the slopes from plots of In D versus pressure for both DPPC (37 ml/mol at 50 degrees C, 34 ml/mol at 60 degrees C and 25 ml/mol at 70 degrees C) and POPC (16 ml/mol at 5 degrees C, 9 ml/mol at 20 degrees C and 6 ml/mol at 35 degrees C) sonicated vesicles in the LC phase. The activation energy for diffusion (Ea) was calculated using the slopes from plots of In D versus the inverse of the temperature (1/T) for both DPPC and POPC in the LC phase (3.5 kcal/mol and 3.9 kcal/mol, respectively) and for both DPPC and POPC in the GI phase (6.0 kcal/mol and 4.4 kcal/mol, respectively). From the lateral diffusion coefficient and line width data pressure-temperature phase diagrams for sonicated pure DPPC and POPC vesicles were constructed. The values of the temperature to pressure equivalence of DPPC (dTm/dP) were estimated to be 22.1 degrees C/kbar for the LC to GI phase transition and 28.6 degrees C/kbar for the GI to Gi phase transition. The value of the temperature to pressure equivalence of POPC for the LC to GI phase transition was estimated to be 19.0 degrees C/kbar.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

NMR study of the cold, heat, and pressure unfolding of ribonuclease A.

The reversible cold, heat, and pressure unfolding of RNase A and RNase A--inhibitor complex were studied by 1D and 2D 1H NMR spectroscopy. The reversible pressure denaturation experiments in the pressure range from 1 bar to 5 kbar were carried out at pH 2.0 and 10 degrees C. The cold denaturation was carried out at 3 kbar, where the protein solution can be cooled down to -25 degrees C without freezing. Including heat denaturation experiments, the experimental data obtained allowed us to construct the pressure--temperature phase diagram of RNase A. The experimental results suggest the possibility that all three denaturation processes (cold, heat, and pressure) lead to non-cooperative unfolding. The appearance of a new histidine resonance in the cold-denatured and pressure-denatured RNase A spectra, compared to the absence of this resonance in the heat-denatured state, indicates that the pressure-denatured and cold-denatured states may contain partially folded structures that are similar to that of the early folding intermediate found in the temperature-jump experiment reported by Blum et al. [Blum, A. D., et al. (1978) J. Mol. Biol. 118, 305]. A hydrogen-exchange experiment was performed to confirm the presence of partially folded structures in the pressure-denatured state. Stable hydrogen-bonded structures protecting the backbone amide hydrogens from solvent exchange were observed in the pressure-denatured state. These experimental results suggest that the pressure-denatured RNase A displays the characteristics of a the inhibitor 3'-UMP show that the RNase A-inhibitor complex is more stable than RNase without the inhibitor.

Animals↗
PubMed1995

One and two dimensional 1H-NMR studies of pressure and tetracaine effects on sonicated phospholipid vesicles.

One and two dimensional 1H-NMR experiments have been performed to study the molecular order and dynamics of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles under the influence of high pressure and the local anesthetic, tetracaine (TTC), which can also be considered as a model-charged amphiphile. The TTC molecules have an ordering effect on the headgroups but a disordering effect on the acyl chains, whereas, pressure has an ordering effect on the acyl chains. The results from 2D NOESY experiments on pure DPPC vesicles show that the intensities of NMe3/CH3, NMe3/(CH2)n, and CH3/(CH2)n cross-peaks increase with increasing pressure in the liquid-crystalline phase but decrease with pressure in the gel phase, further suggesting that the appearance of the cross-peaks between the two extremes of the DPPC molecules is due to spin-diffusion. For the DPPC/TTC vesicles, the 2D NOESY experiments confirm that charged TTC molecules are located in the headgroup region of the DPPC bilayers and, in the gel phase, also suggest the formation of an interdigitated gel phase.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

High pressure 2H-NMR study of the order and dynamics of selectively deuterated dipalmitoyl phosphatidylcholine in multilamellar aqueous dispersions.

High pressure 2H multipulse NMR techniques were used to investigate the effects of pressure on the structure and dynamics of selectively deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) multilamellar aqueous dispersions. The samples were deuterated on both chains at positions 2, 9, or 13. The deuterium lineshapes, the spin-lattice relaxation times, T1, and the spin-spin relaxation times, T2, were measured as a function of pressure from 1 bar to 5 kbar at 50 degrees C for the three deuterated DPPC samples. This pressure range permitted us to explore the phase behavior of DPPC from the liquid-crystalline (LC) phase through various gel phases such as the Gel I (P beta), Gel II (L beta), Gel III, Gel X, and the interdigitated, Gel i, gel phase. Pressure had an ordering effect on all chain segments both in the LC phase and various high pressure gel phases as indicated by the increase in SCD bond order parameter and the first moment, M1, with pressure. Compared with the adjacent gel phases, the Gel i phase had the highest order. Also, in all gel phases the carbon-9 segment of the chains had the most restricted motions in contrast to the LC phase, where the carbon-2 segment was the most restricted. In the LC phase, T1 and T2 values for all segments decreased with pressure, indicative of the fast correlation time regime. Similarly, T1 decreased with pressure in the Gel I and the interdigitated Gel i gel phases but changed to the slow correlation time regime at the Gel i/Gel II phase transition. For T2, which reflects slow motions, the transition to the slow correlation time regime occurred already at LC/Gel I phase transition. Considering the various motions which contribute to relaxation, the behavior of T1 and T2 in the Gel 11 through Gel X phases showing discontinuities and slope changes at the phase transitions was, as expected, quite complex.In addition we found a straight line relationship for T-1 vs. S2D, and T-1 vs. S2CD for the deuterons in the 9 and 13 positions in the LC phase in the pressure range investigated.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

[Risks and follow-up after crural vascular reconstruction in the extremity at risk for ischemia].

After 36 crural bypass operations the operative risk and the long-term results were analyzed in 34 patients. For reconstruction autologous vein (n = 12), a composite graft (saphenous vein and PTFE, n = 10) and in 14 cases a 6 mm PTFE graft were used. In 18 cases a monobypass, in another 16 patients a jump graft and in two patients a sequential bypass were performed. Postoperative complications were seen in 16.7%. An early bypass occlusion was seen in one patient, an amputation was necessary in 2 patients. After 1,2 and 3 years the bypass patency rate was 85%, 67% and 67%. The long-term results were dependent on the bypass material. The best results were seen with vein or composite grafts with a 3 year patency rate of 82% in contrast to only 39% of a PTFE graft.

Aged↗
PubMed1994

High-pressure NMR study of the dissociation of Arc repressor.

Different denatured states of Arc repressor were characterized by one-dimensional and two-dimensional NMR and by fluorescence spectroscopy. Increasing pressure promoted sequential changes in the structure of Arc repressor: from the native dimer through a predissociated state to a denatured molten globule monomer. A compact state (molten globule) of Arc repressor was obtained in the dissociation of Arc repressor by pressure whereas high temperature and urea induced dissociation and unfolding to less structured conformations. The NMR spectra of the monomer under pressure (up to 5.0 kbar) are typical of a molten globule, and they are considerably different from those of the native dimer and the thermally or chemically denatured monomer. The substantial line broadening and overlap of many resonances in the NMR spectra at high pressures indicate that there is interconversion between a number of different conformations of the molten globule at an intermediate exchange rate. The two-dimensional NOE spectra show that the pressure-denatured monomer retains substantial secondary structure. The presence of NOEs in the beta-sheet region in the dissociated state suggests that the intersubunit beta-sheet (residues 6-14) in the native-dimer is replaced by an intramonomer beta-sheet. Changes in 2D NMR spectra prior to dissociation indicate the existence of a predissociated state that may represent an intermediate in the folding and subunit association pathway of Arc repressor.

Macromolecular Substances↗
PubMed1994

[Diagnosis and prognosis of mesenterial infarct].

RESULTS: 28 cases of arterial thrombosis, 18 arterial embolism, 16 venous thrombosis and twelve cases of nonocclusive intestinal ischemia were diagnosed. History of symptoms on admission was longer in venous thrombosis (80 hours) than in arterial vascular occlusion (40 hours). There was a leukocytosis of 19.7/nl and lactate in serum was elevated in 85.1% of patients. Sonographic abdominal examination without preparation of the gut was normal in 44.6% (33/74 patients), variable distended loops of small intestine in the other cases. Sonographic measurement of mesenteric vascular flow succeeded only in 10.9%. Abdominal X-ray photography showed no characteristic signs in 21.6%. Variable degree of gaseous distension and fluid levels was described in 73.7%. Angiography was only performed in patients which were not supposed to be operated because of clinical examination (e.g. peritonitis). Eleven of 19 cases were diagnosed correctly (specificity 73.7%). Mortality rate of all patients was 70.3% and showed in further analysis significant differences in age, etiology of mesenteric ischemia, the length of ischemic and operatively resected gut. CONCLUSION: If mesenteric vascular occlusion is suspected a quick diagnostic procedure and laparotomy for resection of gangrenous bowel is to be planned.

Aged↗
PubMed1994

Nuclear relaxation of liquids in confinements.

We study theoretically the effects of geometrical confinement on the dipolar relaxation of a non-interacting liquid in porous media. Application to the 1H relaxation of methylcyclohexane liquid in porous silica glasses is given. The case of an interacting liquid is considered by molecular dynamics simulations. Geometrical confinement and surface interaction lead to similar frequency behaviour of relaxation rates according to the layering of local density and anisotropy of the molecular mobility.

Eyeglasses↗