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Biomedical subjects

J Frank

Publications and source records attributed to J Frank.

At least 217 records · Page 12Linked to original sources
PubMed1995

Double-tilt electron tomography.

Fidelity of tomographic reconstructions is improved and reconstruction artifacts are reduced, without increasing the number of projections, by combining tilt series taken around two orthogonal axes. Test reconstructions were made from high-voltage EM of rat liver mitochondria in a 0.6 micron thick plastic section. A number of schemes for selecting tilt angles for the projections are compared. A new method for aligning fiducial markers is described. It uses an iterative algorithm to determine the shift, scale, in-plane rotation and tilt angle for each tilt image, enforcing agreement of the expected locations of the fiducial markers in 3D space. These 3D locations are used to find the orientation between two tilt series and to merge both sets of projections.

Animals↗
PubMed1995

Approaches to large-scale structures.

Quantitative three-dimensional (3D) maps of large-scale structures can now be routinely obtained by the use of high- or intermediate-voltage electron tomography. The recent 3D reconstructions of the mitochondrion and the Golgi apparatus highlight both the potential and the shortcomings of this technique. New technological developments, in particular the development of automated low-dose electron tomography, are expected to facilitate the 3D visualization of large structures in the fully hydrated environment, embedded in vitreous ice.

Animals↗
PubMed1995

Levodopa reduces muscle tone and lower extremity tremor in Parkinson's disease.

OBJECTIVE: We have quantified the effects of levodopa treatment in Parkinsonian subjects during maintained stance. METHODS: Electromyographic muscle activity during quiet stance was assessed in subjects with Parkinson's disease, who exhibited a fluctuating response to levodopa, and in age-matched control subjects. Stance stability was also assessed from mean displacement and velocity of the center of pressure excursions during stance. RESULTS: Lower extremity and trunk muscles showed high amplitude activity in all Parkinson's subjects when "off", and a 4-5 Hz tremor in three of these subjects. When "on", the amplitude of muscle activity was reduced in the distal muscles more than the proximal, while tremor was suppressed in all muscles. Corresponding to the excessive muscle activity, the Parkinson's subjects had increased velocity and variability of velocity in the anterior-posterior center of foot pressure excursions, but the mean displacement of the center of pressure excursion was not different from the controls. The velocity of center of pressure excursions in the Parkinson's subjects "on", approached those of the control subjects suggesting that the excessive distal muscle amplitude and tremor contributed to the high velocity of the center of pressure. CONCLUSIONS: These findings suggest that dopaminergic systems are involved in the regulation of muscle tone during stance. Depletion of dopaminergic transmission results in increased muscle tone and tremor in the lower extremities which may contribute to changes in posture and stability.

Aged↗
PubMed1995

Estimation of variance distribution in three-dimensional reconstruction. I. Theory.

A theory is developed for estimating the three-dimensional (3-D) variance of a 3-D image reconstructed from projections by weighted backprojection. The theory is applicable for any data-collection schemes that produce partially redundant sampling of the angular space. The particular data collection considered here, the single-exposure random-conical scheme, is used for the reconstruction of macromolecules in electron microscopy. In this context, the purpose of the 3-D variance estimation is to detect and localize the conformational variability, to assess the significance of structural differences between two experimentally related 3-D images, and to assess the significance of local features in a 3-D image. The 3-D variance estimate of each reconstruction voxel is obtained by (i) the comparison of closest points on Fourier sections associated with difference projections, (ii) the comparison of neighbor projections in real space, or (iii) the comparison of projections with reprojections of the reconstruction.

Fourier Analysis↗
PubMed1995

Estimation of variance distribution in three-dimensional reconstruction. II. Applications.

A previously developed theory of three-dimensional (3-D) variance estimation [J. Opt. Soc. Am. A 12, 2615-2627 (1995)] is applied to the structural study of a hemocyanin-Fab complex with the electron microscope. The precise locations of structurally variable regions of the macromolecule are determined from the 3-D variance maps. The structural differences among different classes of the macromolecular complex are assessed by the use of the statistical t-test, and the 3-D antibody binding sites are revealed. From a model analysis, a rule is demonstrated for visually identifying a 3-D conformational change by the inspection of the 3-D variance map. Our analysis lays the foundation for numerous practical applications of variance estimation in the 3-D imaging of macromolecules.

Analysis of Variance↗
PubMed1995

[Antioxidants in nutrition and their importance in the anti-/oxidative balance in the immune system].

Free radicals and reactive oxygen species can damage cells and tissues of biological organisms. Due to the fact that these compounds are generated continuously in living cells defense mechanisms must exist. This so-called antioxidative system ensures that the formation of free radicals during different physiological processes does not result in cellular damage. Free radicals (oxidants) are produced form the immune system. The purpose of this immune cell products is to destroy invading organisms and damaged tissue. Oxidants enhance IL-1, IL-8 and TNF production in response to inflammatory stimuli. Sophisticated antioxidant defense systems like enzymes or vitamins protect directly and indirectly the host against the damaging influence of oxidants. While endogenous systems can hardly be influenced, exogenous antioxidants, delivered by the diet, can be upregulated in the body. By this way the pro-/antioxidative capacity can be balanced or even unbalanced.

Animals↗
PubMed1994

Separation of selenium analogues of sulphur-containing amino acids by high-performance liquid chromatography and high-resolution gas chromatography.

The historically conditioned adaptation of living organisms to chemically corresponding elements is influenced in nature by anthropogenic activities in many regions, the selenium-sulphur pair being one example of such a case. The separation of selenomethionine, selenoethionine and selenocystine was studied by HPLC and high-resolution GC. Ion-exchange chromatography followed by temperature-programmed GC gives the possibility of the analytical separation of trace amounts of selenomethionine in a complex mixture of common amino acids. Diastereoisomers of selenocystine were identified by HPLC in the AccQ-Tag mode.

Amino Acids, Sulfur↗
PubMed1994

A novel dye-linked formaldehyde dehydrogenase with some properties indicating the presence of a protein-bound redox-active quinone cofactor.

Dye-linked formaldehyde dehydrogenase from methylamine-grown Hyphomicrobium zavarzinii ZV 580, a tetramer of M(r) 210,000 with subunits of M(r) 54,000, was purified to homogeneity in five steps with 10% yield. The enzyme shows optimal affinity for, and activity with, formaldehyde (Km 67 microM) compared with other aldehydes. Pyridoxal phosphate, pyrroloquinoline quinone and other cofactors that would give the enzyme a distinctive absorption spectrum are absent. Slight changes are observed in the spectrum at 300-550 nm on oxidation of the enzyme with Wurster's Blue (WB) and reduction with formaldehyde. Titration of the native reduced enzyme with WB accounts for 2 mol of electrons per mol of tetrameric enzyme. The circumstantial evidence supporting the presence of a redox-active quinone cofactor bound to the polypeptide chain comprises a signal at g = 2.0049 in the X-band e.p.r. spectrum of the enzyme oxidized with WB, which disappears on reduction with formaldehyde, and a positive reaction of the native as well as the denatured and dialysed enzyme in the redox-cycling assay with glycinate and NitroBlue Tetrazolium (quinone staining). The oxidized enzyme is inhibited by equimolar amounts of phenylhydrazine, which is also a reductant. Hydrazone formation was absent with completely inhibited enzyme, according to photometric evidence. Likewise, the glycinate-dependent reduction of NitroBlue Tetrazolium was not affected by the inhibitor. It is concluded that an oxidation product of the hydrazine is the actual inhibitor which reacts with an amino acid residue of the active site rather than with the prospective quinone cofactor.

Aldehyde Oxidoreductases↗
PubMed1994

Quaternary structure of Octopus vulgaris hemocyanin. Three-dimensional reconstruction from frozen-hydrated specimens and intramolecular location of functional units Ove and Ovb.

A frozen-hydrated sample of Octopus vulgaris hemocyanin was imaged at 0 degree and 40 degrees tilt angle under low dose conditions by transmission electron microscopy. A three-dimensional reconstruction by the method of random conical tilt series produced a three-dimensional volume to which a D5 symmetry was applied. Examination of serial sections in the volume and surface representation at various thresholds allowed the five arches containing functional unit Ovg to be localized at the interdimeric subunit groove. In another set of experiments specific polyclonal antibodies were used to label functional units Ovb and Ove in the cylinder wall. The observation of the negatively stained immunocomplexes showed that Ovb is located in the external tiers of functional units and Ove in the internal tier. These results suggest that the direction of the polypeptide chains in the cylinder wall may be only partially antiparallel. A model of the quaternary structure is proposed with the following features: (1) the external tiers of functional units comprise four units each (Ova-d) coming from a single polypeptide chain; (2) the internal tier comprises two functional units from each polypeptide chain (Ove-f); (3) the interdimeric subunit arches connect the two copies of a single functional unit (Ovg) located in each polypeptide chain.

Animals↗
PubMed1994

The internal compartmentation of rat-liver mitochondria: tomographic study using the high-voltage transmission electron microscope.

The three-dimensional organization of the internal compartments of conventionally fixed and embedded rat-liver mitochondria has been determined by tomographic reconstruction from tilt-series images collected on the Albany high-voltage electron microscope. The results indicate that the inner membranes of these organelles are predominantly tubular in the orthodox (expanded matrix) conformation, as previously suggested by scanning electron microscopy. In the condensed (contracted matrix) conformation, the intracristal space opens up into large irregularly shaped compartments which are connected to each other and to the external (intermembrane) space by tubes with approximately the same diameter (20 nm) as those observed in the orthodox state. These results raise several questions, in particular about the nature of the structural transitions that occur in the cristae during matrix expansion and contraction, and about the influence of inner-membrane shape on the diffusion of ions and metabolites between the intracristal and intermembrane compartments.

Animals↗
PubMed1994

MRI detects acute degeneration of the nigrostriatal dopamine system after MPTP exposure in hemiparkinsonian monkeys.

Exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can cause an acute chemical toxicity resulting in a parkinsonian state in humans and nonhuman primates. We wished to assess whether the toxicity from MPTP is associated with changes on magnetic resonance images of brain structures containing dopamine neuronal processes or with disrupture of the blood-brain barrier. Normal rhesus monkeys and monkeys at various times after being subjected to unilateral intracarotid injection of MPTP (0.4 mg/kg) were studied with magnetic resonance imaging using T1- and T2-weighted spin-echo and gradient-echo sequences. Disrupture of the blood-brain barrier was assessed also with magnetic resonance imaging after administration of gadolinium-diethylenetriamine pentaacetic acid. Parkinsonian symptoms contralateral to the infused carotid usually appeared within 1 day after MPTP exposure, reaching their peak severity by 7 days, when all monkeys showed clear clinical abnormalities. Magnetic resonance imaging changes developed in concomitance with the clinical signs and were characterized by increased signal intensity on T2-weighted images as well as decreased intensity on T1-weighted images of the ipsilateral caudate and putamen. T2 hyperintensity was also present just dorsal to the pars compacta of the substantia nigra, in the region of the proximal nigrostriatal tract. All magnetic resonance imaging changes dissipated in the next 2 weeks. There were no abnormalities at any time in the globus pallidus, nucleus accumbens, and other structures innervated by the mesocorticolimbic dopamine system. After MPTP exposure, there was no evidence of blood-brain barrier disrupture, suggesting that vasogenic edema was an unlikely factor in the production of the observed abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1994

The ribosome at improved resolution: new techniques for merging and orientation refinement in 3D cryo-electron microscopy of biological particles.

Cryo-electron microscopy of single biological particles opens up new possibilities for structure analysis: the particle can be reconstructed in its native shape and internal features are preserved. To take advantage of these possibilities we have developed new methods of data collection and image processing and we have applied them to the 70S Escherichia coli ribosome. A method of orientation search is proposed, which makes it possible to relate random-conical data sets to one another even if they are collected from low-tilt micrographs. A technique for 3D alignment of projections is described and applied to the single-micrograph 3D reconstruction.

Escherichia coli↗
PubMed1994

Functional brain MR imaging based on bolus tracking with a fast T2*-sensitized gradient-echo method.

Dynamic physiological scanning, based on temporary changes in local field homogeneity during the passage of a contrast agent bolus, has been performed hitherto with echo-planar imaging (EPI) or conventional gradient-recalled techniques (FLASH). Here, it is shown that the T2* sensitivity of conventional FLASH techniques can be improved drastically on a conventional whole body instrument by delaying the gradient-echo until the subsequent TR-period without increasing total imaging time. Examples are given for a full k-space matrix (128 x 256) obtained within 2 s with a TE of 25 ms, resulting in images free of artifacts. The method is applied to bolus tracking through the brain of healthy volunteers during visual stimulation and in the dark. An average increase of regional cerebral blood volume (rCBV) in the visual cortex of 10.9% (n = 9, p = .001) was found.

Blood Volume↗
PubMed1994

Cryo-electron microscopy and three-dimensional reconstruction of the calcium release channel/ryanodine receptor from skeletal muscle.

The calcium release channel (CRC) from skeletal muscle is an unusually large tetrameric ion channel of the sarcoplasmic reticulum, and it is a major component of the triad junction, the site of excitation contraction coupling. The three-dimensional architecture of the CRC was determined from a random conical tilt series of images extracted from electron micrographs of isolated detergent-solubilized channels prepared in a frozen-hydrated state. Three major classes of fourfold symmetric images were identified, and three-dimensional reconstructions were determined for two of these. The two independent reconstructions were almost identical, being related to each other by a 180 degrees rotation about an axis in the plane of the specimen grid. The CRC consists of a large cytoplasmic assembly (29 x 29 x 12 nm) and a smaller transmembrane assembly that protrudes 7 nm from one of its faces. A cylindrical low-density region, 2-3 nm in apparent diameter, extends down the center of the transmembrane assembly, and possibly corresponds to the transmembrane Ca(2+)-conducting pathway. At its cytoplasmic end this channel-like feature appears to be plugged by a globular mass of density. The cytoplasmic assembly is apparently constructed from 10 or more domains that are loosely packed together such that greater than 50% of the volume enveloped by the assembly is occupied by solvent. The cytoplasmic assembly is suggestive of a scaffolding and seems well adapted to maintain the structural integrity of the triad junction while allowing ions to freely diffuse to and away from the transmembrane assembly.

Animals↗
PubMed1994

Hepatocyte isolation from pig livers after warm ischaemic injury.

Hepatocyte cultures have been used extensively for a wide variety of physiological, pharmacological and experimental studies. The warm ischaemic period before isolation is kept to a minimum to achieve a high yield of cells isolated and a good viability for culture. We have recently introduced a new concept of liver resuscitation after warm ischaemia that is based on a 3-h reperfusion period with an improved perfusate and simultaneous dialysis. In this study, we applied the new technique for hepatocyte isolation from livers subjected to 80 min of complete ischaemia at 37 degrees C. Cell yield was improved by a resuscitating perfusion from 58% to 73% and viability from 39% to 76%.

Alanine Transaminase↗
PubMed1994

An ultrastructural study of lipoprotein accumulation in cardiac valves of the rabbit.

Heart valves are composed chiefly of extracellular matrix surrounded by an endothelial cell monolayer and as a result are an excellent model of the intima. Heart valves from rabbits fed a high-cholesterol diet accumulate lipids within the matrix and over time develop fatty streaks similar to those seen in the aorta. In this study we demonstrate that the heart valves (atrioventricular and aortic) can be isolated and used as an in vitro preparation to control and follow low-density lipoprotein (LDL) uptake and deposition. Using thin-section and freeze-etch microscopy we found that LDL rapidly associates with collagen within the extracellular matrix. As it accumulates along the collagen fibers the LDL appears to undergo structural changes in size and surface topography. This association of LDL with collagen may be a key step in lipid aggregation in the intima.

Animals↗
PubMed1994

[Chronic fatigue syndrome: immune dysfunction, role of pathogens and toxic agents and neurological and cardial changes].

375 patients with chronic fatigue syndrome (CFS) were examined using a standardized questionnaire and subsequent interview on 11 risk factors and 45 symptoms. Additionally immunologic, serologic, toxicologic, neuroradiologic, neurophysiologic and cardiologic investigations were performed. Immunologic tests showed cellular immunodeficiences particularly in functional regard (pathological lymphocyte stimulation in 50% of the patients, disorders of granulocyte function in 44%). Furthermore variable deviations were found in the lymphocyte subpopulations (CD3, CD4, CD8, CD19, DR, Leu 11 + 19). In the humoral part tendencies to low IgG-3- and IgG-1-subclass-levels occurred (59% respectively 11% of the patients) also as decreases in complement system (CH50, C3, C4, C1-esterase-inhibitor). In the group of activation markers and cytokines 42% of the investigated patients had circulating immune complexes (CIC), 47% increases of tumor-necrosis-factor (TNF-a) and 21% increases of soluble interleukin-2-receptor (IL-2-R). The increased occurrence of autoantibodies in the CFS-patients (specially antinuclear anti-bodies [ANA], microsomal thyroid antibodies) suggest, that CFS is associated with or the beginning of manifest autoimmune disease. Under the pathogens 78% of the patients had a striking serological constellation of Epstein-Barr-Virus (EBV-EA positive, low EBNA-titers), in the HHV-6-Virus 47% showed increased antibody-titers. Tests on further herpes viruses and on Borreliae, Chlamydiae, Candida and Amoebae were positive in 8 to 36% of the examined patients. Furthermore there were found variable deficits of vitamins and trace elements also as hormonal disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗