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Biomedical subjects

A Engel

Publications and source records attributed to A Engel.

At least 19 recordsLinked to original sources
PubMed1992

[Sympathetic reflex dystrophy. Effectiveness of physical therapy treatment of Sudeck's syndrome].

To investigate the impairment of patients with reflex sympathetic dystrophy syndrome (RSDS) and to establish the effectiveness of two physiotherapeutic regimens in the treatment of this entity, 54 RSDS patients were examined clinically, radiologically and scintigraphically an average of 112 days after the triggering event. The patients were assigned to either of two treatment groups in accordance with the results of preliminary scintigraphic examinations. After physiotherapy comprising exercises and cryotherapy either with or without galvanic stimulation, a significant therapeutic effect on clinical and scintigraphic parameters was found in both treatment groups. Scanning, in combination with clinical diagnostic measures proved a valuable tool in the diagnostic evaluation, selection of treatment and follow-up in patients with RSDS.

Combined Modality Therapy↗
PubMed1992

Two-dimensional crystals of Escherichia coli maltoporin and their interaction with the maltose-binding protein.

We have reconstituted Escherichia coli maltoporin into phospholipid membranes at low lipid-to-protein ratios to produce two-dimensional crystals of this membrane protein. Electron microscopy of negatively stained membranes showed three different types of arrays, two of them hexagonal and the third rectangular, all diffracting to approximately (2 nm)-1. Furthermore, we have core-constituted maltoporin with the maltose-binding protein from E. coli, a soluble periplasmic protein that has been proposed to interact with maltoporin. One of the hexagonal arrays was found to bind maltose-binding protein molecules in a regular way, while the maltose-binding protein binding sites were not accessible in the other crystal forms. Difference maps from averaged decorated arrays and undecorated controls showed three symmetry-related maltose-binding protein binding sites per maltoporin trimer, of which not more than one is likely to be occupied at a given time. Using multivariate statistical analysis to select similar unit cells of the decorated maltoporin array, we have obtained a map showing the rough outline of a maltose-binding protein molecule interacting with the pore formed by a maltoporin trimer.

ATP-Binding Cassette Transporters↗
PubMed1992

Ubiquitous soluble Mg(2+)-ATPase complex. A structural study.

We have performed a detailed structural analysis of the soluble Mg(2+)-ATPase complex purified from Xenopus laevis ovary, which is an abundant and ubiquitous homo-oligomeric protein complex located in the nucleus and in the cytoplasm, belonging to a novel multigene-family of putative Mg(2+)-ATPases. Enzyme activity staining after non-denaturing polyacrylamide gel electrophoresis revealed that Mg(2+)-ATPase activity of the native protein is dependent on oligomerization and could not be detected in dissociated subunits. For the native protein a sedimentation coefficient of 15.3 S and a corresponding relative molecular mass of 612,000 was determined by analytical ultracentrifugation and a relative molecular mass of 590,000 was estimated from scanning transmission electron microscopy, supporting our previous conclusion that the oligomer comprises six 97,000 Mr subunits. Conventional electron microscopy of negatively stained specimens revealed the Mg(2+)-ATPase complex to be a hexagonal molecule in its favoured "end-on" projection and a double-banded molecule in its "side-on" projection (approx. 12 nm diameter; approx. 9 nm height). In addition, dimerized complexes could be observed in negatively stained specimens, yielding pronounced hexameric images and four-banded images in their end-on and side-on orientations, respectively (approx. 12 nm diameter; approx. 18.5 nm height). Two-dimensional (2D = mono-molecular) crystals have been produced from the dimerized complexes by the negative staining carbon film technique. Hexagonal crystals with a p6 plane group symmetry were obtained from molecules in their end-on orientation and longitudinal arrays with a p2 symmetry from complexes in their side-on orientation. A low-resolution molecular model of the native protein, derived from averages of these two 2D crystals, is presented. From our results we propose oligomerization as an inherent structural principle of organization for this whole newly defined Mg(2+)-ATPase multigene-family, that includes such seemingly diverse functionally defined proteins as mammalian and yeast "vesicle fusion" and "peroxisome assembly" proteins and the product of the yeast cell cycle gene CDC48.

Animals↗
PubMed1992

Analysis of the structure of photosystem I in cyanobacterial thylakoid membranes.

Using electron microscopy of negatively stained specimens, we have investigated the shape and degree of association of photosystem (PS) I complexes in cyanobacterial thylakoid membranes. When incubated at high concentrations of magnesium chloride (greater than 0.15 M), the PSI complexes form small ordered arrays in the membrane composed of monomeric complexes in a P1 square lattice of dimensions a = b = 11 nm. Averaged projections of the complex resemble those found for the purified PSI reaction centre after reconstitution (Ford, R.C, Hefti, A. and Engel, A. (1990) EMBO J. 9, 3067-3075). Some small differences in its shape are discussed, with particular reference to the differences in the polypeptide composition of the 2 preparations. We find that the complex remains in the monomeric form in the thylakoid membrane under all the conditions tested.

Cyanobacteria↗
PubMed1992

Subunit stoichiometry and three-dimensional arrangement in proteasomes from Thermoplasma acidophilum.

The proteasome or multicatalytic proteinase from the archaebacterium Thermoplasma acidophilum is a 700 kDa multisubunit protein complex. Unlike proteasomes from eukaryotic cells which are composed of 10-20 different subunits, the Thermoplasma proteasome is made of only two types of subunit, alpha and beta, which have molecular weights of 25.8 and 22.3 kDa, respectively. In this communication we present a three-dimensional stoichiometric model of the archaebacterial proteasome deduced from electron microscopic investigations. The techniques which we have used include image analysis of negatively stained single particles, image analysis of metal decorated small three-dimensional crystals after freeze-etching and STEM mass measurements of freeze-dried particles. The archaebacterial and eukaryotic proteasomes are almost identical in size and shape; the subunits are arranged in four rings which are stacked together such that they collectively form a barrel-shaped complex. According to a previous immunoelectron microscopic investigation, the alpha-subunits form the two outer rings of the stack, while the two rings composed of beta-subunits, which are supposed to carry the active sites, are sandwiched between them. Each of the alpha- and beta-rings contains seven subunits; hence the stoichiometry of the whole proteasome is alpha 14 beta 14 and the symmetry is 7-fold. Image simulation experiments indicate that the alpha- and beta-subunits are not in register along the cylinder axis; rather it appears that the beta-rings are rotated with respect to the alpha-rings by approximately 25 degrees. In contrast to some previous reports we have not been able to find stoichiometric amounts of RNA associated with highly purified proteolytically active proteasome preparations.

Crystallization↗
PubMed1992

2D crystallization: from art to science.

The techniques as well as the principles of the 2D crystallization of membrane and water-soluble proteins for electron crystallography are reviewed. First, the biophysics of the interactions between proteins, lipids and detergents is surveyed. Second, crystallization of membrane proteins in situ and by reconstitution methods is discussed, and the various factors involved are addressed. Third, we elaborate on the 2D crystallization of water-soluble proteins, both in solution and at interfaces, such as lipid monolayers, mica, carbon film or mercury surfaces. Finally, techniques and instrumentations that are required for 2D crystallization are described.

Aluminum Silicates↗
PubMed1992

Has negative staining still a place in biomacromolecular electron microscopy?

Transmission electron microscopy of proteins has provided molecular- and in a few cases near-atomic-resolution structural information. In this review, we critically evaluate the potential and the limitations in obtaining molecular resolution, particularly with negatively stained specimens, and put these into perspective with cryomicroscopy of unstained frozen-hydrated and sugar-embedded preparations.

Histocytological Preparation Techniques↗
PubMed1992

[Sonographic structural analysis of the Achilles tendon and biomechanical implications].

Ruptures of the Achilles tendon mainly occur on the ground of predisposing destruction of tendon structure. The aim of this retrospective US study was to evaluate the location and extent of tendon abnormalities. 62 patients (49 male, 13 female; 19 to 57 years, mean 38) with achillodynia of short duration and/or clinically suspected tendon abnormalities were evaluated sonographically. Together with a review of the literature, US findings (location, extent, and echo pattern) were compared with clinical findings. With US, abnormalities could be detected with a sensitivity of 0,76 and a specificity of 0.9. Pathologic lesions could be grouped as follows: (1) pain without any clinical signs or US findings (tenalgia); (2) nodular tendinitis which in 52% appeared in the form of a tiny hypoechoic lesion in the ventromedial part of the tendon 2-3 cm proximal to the os calcis; (3) peritendinal oedema; (4) circumscribed tendon swelling, (5) extensive inhomogeneities of tendon structure. With US, abnormalities of the Achilles tendon may be detected at an early stage of the disease and hence the risk of tendon rupture may be predicted to better advantage.

Achilles Tendon↗
PubMed1992

Histamine-induced bronchoconstriction in conscious guinea pigs measured by strain-gauge transduction. A new method.

A new objective method for measuring histaminedihydrochloride-induced bronchoconstriction in conscious guinea pigs has been developed. The aim of the present work was to investigate whether identical results could be obtained when the clinical observation of conscious guinea pigs with symptoms of respiratory distress (bronchoconstriction) was compared to an objective measuring technique of this parameter. An evaluation of the repeatability of the method was made and the respiration frequence (fR) and histaminedihydrochloride challenge concentration were compared to see whether there was a correlation between the two. Consequently, an apparatus was built that allowed simultaneous recording of breathing pattern and clinical observation of the animal being challenged. The breathing pattern was recorded by a strain-gauge transducer, connected to a measuring bridge, and the curves obtained on a jet ink x-y writer were used for calculating changes in duration of expiratory phase (Te) and fR. During the attacks of histaminedihydrochloride-induced bronchoconstriction a significantly prolonged Te could be calculated from the respiration curves. A high degree of agreement was found between this objective measure and clinically observed respiratory distress. The repeatability of the method was comparable to that of corresponding methods used for histaminedihydrochloride challenge in man. No obvious correlation was found between changes in fR and histaminedihydrochloride challenge concentration.

Animals↗
PubMed1991

Density determination by analytical ultracentrifugation in a rapid dynamical gradient: application to lipid and detergent aggregates containing proteins.

A rapidly developing dynamical gradient can be formed in the analytical centrifuge when a buffer solution prepared in D2O is underlayered under the same buffer solution prepared in H2O in a specially designed double sector cell. In a short time the boundary layer spreads to form the gradient. Heavy particles (S greater than or equal to 10S) will band in the gradient corresponding to their density, which can be determined accurately. To this end, the buffer may contain density adjusting additives such as sucrose. We present results with this technique for lipid vesicles, for a Ca-antagonist bound to vesicles, as well as for a lipoprotein and reconstituted regular membrane protein-lipid arrays.

Animals↗
PubMed1991

Scanning transmission electron microscopic mass determination of in vitro self-assembled smooth muscle myosin filaments.

We have measured the mass per unit length of in vitro self-assembled smooth muscle myosin filaments, using scanning transmission electron microscope darkfield images of freeze-dried samples. The measured values were integral multiples, usually 1, 2, 3 or 4, of 75 kDa per nm. The data corroborate an earlier proposal, that these filaments are built from monolayer sheets of molecules, each sheet having two antiparallel myosin molecules per 14.3 nm of its length.

Animals↗
PubMed1991

[Computed tomography in the diagnosis of popliteal artery entrapment syndrome].

Popliteal artery entrapment syndrome (PAES), a rare cause of lower limb ischemia, is due to an anomalous relationship between the popliteal artery and the gastrocnemius muscle in the popliteal fossa. Hypertrophy of the muscle, or its anomalous insertion, can displace or compress the artery, leading to stenosis or obstruction. It is clinically manifested by intermittent claudication and most often occurs in young, healthy men. Arteriography is the method of choice to demonstrate vascular lesions, but it can only visualize change in the course of vessels or intrinsic lesions. Due to its high spatial and density resolution, CT scan can differentiate between bony structures, vessels, muscles, and fatty tissue in the popliteal fossa. It is therefore a very useful supporting examination in PAES and can demonstrate whether or not stenosis or occlusion of the artery results from causes outside the artery itself.

Arterial Occlusive Diseases↗
PubMed1991

Bilateral stress fracture of the scaphoid. A case report.

Bilateral stress fractures of the scaphoid bones in a gymnast are reported and discussed with special consideration of the possible differential diagnoses; bipartite scaphoid and pseudarthrosis of the scaphoid bone. The relevance of the mechanical factors involved and the abduction and dorsiflexion of the wrist in gymnastics are suggested as likely pathomechanisms.

Adult↗
PubMed1991

Biological structures imaged in a hybrid scanning transmission electron microscope and scanning tunneling microscope.

A hybrid scanning transmission electron microscope (STEM) and scanning tunneling microscope (STM) is described which allows simultaneous imaging of biological structures adsorbed to electron-transparent specimen supports in both modes of scanning microscopy, as demonstrated on uncoated phage T4 polyheads. We further discuss the reproducibility and validity of height data obtained from STM topographs of biomacromolecules and present raw data from topographs of freeze-dried, metal-coated nuclear envelopes from Xenopus laevis oocytes.

Animals↗
PubMed1991

In vitro assembly of gap junctions.

Gap junction structures were assembled in vitro from octyl-beta-D-glucopyranoside-solubilized components of lens fiber cell membranes. Individual pore structures (connexons), short double-membrane structures, and other amorphous material were evident in the solubilized mixture. Following the removal of the detergent by dialysis, these connexons associated to form single- and double-layered, two-dimensional hexagonal arrays (unit cell size a = b = 8.5 nm). The formation of larger arrays was dependent on the lipid-to-protein ratio and the presence of Mg2+ ions. Crystallographic analysis of electron micrographs revealed that lens junctional connexons consisted of six subunits surrounding a stain-filled channel. Upon further detergent treatment, in vitro assembled gap junctions were insoluble and formed three-dimensional stacks while other components were solubilized. SDS-PAGE and mass data from scanning transmission electron microscopy strongly suggest that a 38-kDa polypeptide, which is a processed form of the lens specific gap junction protein MP70, is a major component of the arrays. The in vitro assembly of gap junctions opens new avenues for the structural analysis of gap junctions and for the study of the intermolecular interactions of connexons during junctional assembly.

Animals↗
PubMed1991

Mass analysis of bacteriophage T4 proheads and mature heads by scanning transmission electron microscopy and hydrodynamic measurements.

Quantitative mass analysis of bacteriophage T4 proheads by scanning transmission electron microscopy (STEM) revealed a mass of 79.5 +/- 0.6 MDa, while hydrodynamic measurements yielded a prohead mass of about 80 MDa. This is 25% less than the prohead mass deduced from its polypeptide composition, and this finding implies that the bacteriophage T4 prohead is built of fewer polypeptide copies than previously reported. In contrast, the mass of mature heads measured by STEM, 194 +/- 2 MDa, is in agreement with previous mass measurements of DNA and protein content, and it is consistent with the previously determined stoichiometry. This good agreement of average STEM values for proheads and mature heads with corresponding hydrodynamic measurements suggests that STEM allows faithful evaluation of the masses of large supramolecular assemblies (i.e., greater than or equal to 200 MDa) such as whole viruses or cellular organelles.

Formaldehyde↗