Search PubMed⌕ Search

Biomedical subjects

L Bachmann

Publications and source records attributed to L Bachmann.

At least 55 records · Page 3Linked to original sources
PubMed1991

Correlation of metal decoration and topochemistry on protein surfaces.

On the surface of protein molecules the formation of metal clusters during vacuum condensation is controlled by topochemical features of the substrate and by specific properties of the decorating material. The resulting metal distribution (decoration pattern) can be mapped by electron microscopy in conjunction with image processing. We have applied this technique to freeze-etched crystals of the lumazine synthase-riboflavin synthase complex and its derivative obtained by binding of the heteropolytungstate (NaP5W30O110)(NH4)14.31 H2O. The decoration pattern of the free protein and its heteropolytungstate derivative showed marked differences. The correlation of these data with the X-ray structure of the protein showed an increased affinity of both gold and silver to the location of heteropolytungstate. Decoration sites can, but do not need to, be close to the protein surface. Actually, two of the observed decoration sites are located on a layer of ice as thick as 20 A, which apparently transmits underlying topochemical features. Preferential affinity of a site to a given metal must be seen as a property that depends on specific interaction with the decorating material but also on the differential affinities in adjacent areas.

Bacillus subtilis↗
PubMed1990

Evolution of a telomere associated satellite DNA sequence in the genome of Drosophila tristis and related species.

A highly repetitive satellite DNA sequence from the genome of Drosophila tristis with a length of 181 bp has been cloned in the pUC plasmid. The sequence hybridizes to the telomeres of all chromosomes but the Y of D. tristis and produces a ladderlike hybridization pattern with filterbound genomic DNA of D. tristis digested with Eco RI or Pst I with the hybridization bands at fragment lengths in multiples of 181 bp. A similar pattern is found when the genomic DNA comes from D. ambigua or, though less clear, from D. microlabis. Additional bands appear in the zones of high fragment lengths, too. In D. obscura and D. kitumensis, however, the 181 bp sequence is found in fragments with a length of a few kb only. The 181 bp sequence is tandemly arranged in the genome of D. tristis and has a copy number of about 82,000 per haploid genome (i.e. 10 per cent of the total DNA). A sequence comparison among four independently cloned copies of the family from D. tristis and another homologous sequence from D. obscura, found by chance, shows a one to six per cent variation in basepair composition. However, low divergence (only one per cent) between two copies of D. tristis and between the one of D. obscura and one of D. tristis was observed, and high divergence (six per cent) between these two pairs. This is discussed and explained as the evolutionary consequence of an existing homogenization process by unequal crossing over.

Animals↗
PubMed1989

[Using drugs: experiences with a slide show program and patient questionnaires].

200 patients were surveyed by questionnaire while attending the medical outpatient service at the university hospital of Zürich. Questions related to a slide show on the usage of prescribed drugs presented at the same time in the attending room but also to general personal habits and attitudes regarding pharmacotherapy. Appreciation of the slide show was remarkable. This was substantiated by the observation that next to the physician media such as news papers, television and broadcast serve as source of information on drugs. Patient-compliance was in part related to lack of correct information. While older patients discontinued treatment because of side-effects, younger patients stopped drugs often because of improvement under therapy. In depth information could improve compliance in the latter population since particularly these individuals complained about insufficient instruction. The personal preference of "natural" over "chemical" drugs was surprisingly at variance with the admission of regular intake of prescription drugs--possibly a sign of an ultimately greater confidence in "chemical" drugs.

Audiovisual Aids↗
PubMed1989

Electron microscopy of subnanometer surface features on metal-decorated protein crystals.

Crystals of heavy riboflavin synthase from Bacillus subtilis were freeze-etched and vacuum-coated at normal incidence with 0.1 to 0.4 nm of gold and silver, respectively. This decoration technique was applied to probe the protein surface for preferential nucleation sites. Image processing of the electron micrographs revealed two particular decoration sites for silver and a different one for gold. According to X-ray crystallography, the riboflavin synthase molecules are spherical and smooth except for a surface corrugation of less than 1 nm, which can not be depicted by heavy-metal shadowing. Thus the decoration sites represent sites of specific physical-chemical interactions between the condensing metal and the protein. The decoration pattern correctly reflects the icosahedral symmetry of the almost spherical protein molecules. Owing to the molecule's symmetry, the position of these topochemical sites with respect to the symmetry axes can be localized within 5A. The packing of the molecules in the crystal can be directly observed on shadowed replicas. Only decoration, however, makes it possible to observe the exact orientation of the molecules within the crystal planes and to derive the true lattice constant along the 6-fold screw axis. This proves decoration to be a technique suitable for studying crystal packing and the molecular symmetry of protein complexes at high resolution. The technique can be applied to crystals that are not large enough or insufficiently ordered for X-ray crystallography.

Bacillus subtilis↗
PubMed1986

Heavy riboflavin synthase from Bacillus subtilis. Particle dimensions, crystal packing and molecular symmetry.

Heavy riboflavin synthase from Bacillus subtilis is an enzyme complex consisting of approximately three alpha-subunits (Mr 23.5 X 10(3)) and 60 beta-subunits (Mr 16 X 10(3)). The enzyme has been crystallized from phosphate buffer in a hexagonal crystal modification that belongs to space group P6(3)22. The asymmetric unit of the crystal cell contains ten beta-subunits. The structure of this unusual 10(6) Mr protein has been studied by small-angle X-ray scattering, electron microscopy of three-dimensional crystals, and crystallographic methods. The scattering curves can be interpreted in terms of a hollow sphere model with a ratio of inner and outer radius of 0.3:1. A diameter of 168 A was estimated from the scattering curves, in close agreement with electron microscopic studies. An aggregate with the stoichiometry beta 60, which was obtained by ligand-driven reaggregation of isolated beta-subunits, showed similar shape and dimensions, but a larger value for the ratio Ri/Ra. Electron micrographs of freeze-etched enzyme crystals showed approximately spherical molecules, which were arranged in hexagonal layers. The lattice constants found from the micrographs are in good agreement with the values derived from X-ray diffraction data. Rotation function calculations in Patterson space showed a set of peaks for 2-fold, 3-fold and 5-fold local rotation axes, accurately consistent with icosahedral symmetry and with the particle orientation A shown in the Appendix. The crystal packing can be described as follows: enzyme particles with icosahedral symmetry (point group 532) are located at points 32 of the hexagonal cell, corresponding to positions (0, 0, 0) and (0, 0, 1/2) on the 6-fold screw axes. From the data reported, it may be concluded that the enzyme structure can be described as an icosahedral capsid of 60 beta-subunits with the triangulation number T = 1. The alpha-subunits are located in the central core space of the capsid, but their spatial orientation is incompletely understood.

Bacillus subtilis↗
PubMed1985

Decoration and shadowing of freeze-etched catalase crystals.

Aqueous suspensions of catalase crystals were freeze-cleaved, deep-etched and either shadowed with Ta/W at 45 degrees or decorated with 0.1-0.9 nm thick deposits of Au and Pt at normal incidence. The electron micrographs of the decorated specimens were processed by correlation averaging and compared with a relief reconstruction obtained from shadowed specimens. Pronounced decoration was observed on the catalase crystals at temperatures between 130 and 180 K. Disregarding the difficulties in interpretation, the averages of 0.1-0.2 nm thick Au and Pt films reveal more structural detail than the relief reconstruction. Perfect shadowing provides information on surface topography and is relatively easy to comprehend; decoration renders variations in physico-chemical affinity visible. Problems of the interference of decoration and shadowing effects in the intuitive interpretation of freeze-etch replicas and in relief reconstruction are discussed as well as the disturbing effects of a non-ideal carbon backing. The perspectives of using decoration intentionally as a positive staining technique for the investigation of frozen-hydrated surfaces are evaluated and quality criteria are defined.

Animals↗
PubMed1985

A simple and effective method to teach patients about high blood pressure and obesity.

It is an open question whether information about hypertension and obesity increases compliance with therapy. Nevertheless, patients increasingly demand precise but simple and comprehensive information. A simple slide programme is described which can be demonstrated in any waiting room. The learning effect was assessed in 1083 subjects, of whom 485 had seen the programme completely; 256 subjects served as controls. The percentage of subjects with good or excellent knowledge about hypertension and obesity rose from 22.8% in the controls to 64.2% in the experimental group. Age was the only factor influencing learning, but this was of no great importance in subjects under 70. In particular, social status did not have any significant effect on learning. This programme may be an ideal tool to inform patients about hypertension and obesity and to study the influence of information on compliance with therapy.

Age Factors↗
PubMed1983

[A slide program on hypertension and obesity: a simple method of patient information].

It is well established that information on their disease is one of the prerequisites for improvement of patients' compliance with therapy. The authors have therefore developed a simple slide program presenting information on hypertension and obesity. Consisting of 52 slides, it was shown in the central waiting room of the medical outpatient department at the University Hospital, Zurich. In order to assess learning, 841 patients were asked to fill in a questionnaire. 485 had seen the program and 356 served as controls with the program switched off. Four main results emerged: 1. The percentage of subjects scoring greater than or equal to 4 correct answers (of a maximum of 5) rose significantly from 22.6% to 64.2%. 2. The number of incorrect answers (maximum 3) remained unchanged. 3. Learning decreased with age. 4. Occupation did not have a significant effect on learning. The results clearly show that the program represents an effective method of teaching patients and may therefore serve to improve compliance with therapy.

Adult↗
PubMed1980

Structure of hydrated immunoglobulins and antigen-antibody complexes. Electron microscopy of spray-freeze-etched specimens.

The structure of spray-frozen IgG and IgM, either free in solution or specifically bound to bacterial flagella is compared after freeze-etching with the corresponding preparations negatively stained. The freeze-etched IgG is readily detected; most of the hydrated particles appear approximately spherical with an average diameter of about 12 nm. About 20% are triangular with sides of about 13-14 nm. Antibodies attached to flagella are clearly seen on the top as well as the exposed edges. The technique can thus be used for antigen localization on freeze-etched macromolecules and also on the surface of larger structures. The dimensions and shape of freeze-etched bound IgM confirm the earlier interpretations of the structure of this antibody based on negative staining.

Antigen-Antibody Complex↗
PubMed1977

Structure of pyruvate dehydrogenase complex. Comparison between freeze-etching and negative staining.

Pyruvate dehydrogenase complex (pyruvate : lipoate oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1), from pig heart, was studied by spray freeze etching and negative staining. From freeze etching experiments an average particle weight of 7-10(6) was estimated. Negative staining after glutaraldehyde fixation and freeze etching of unfixed and prefixed enzyme solutions yielded no significant difference in particle dimensions: the majority of the isometric complex molecules measured approximately 400 A in diameter. Tantalum tungsten shadowed freeze etch replicas indicated that the surface of the complex is built up of globular units. The relative positions of these units are in good agreement with the model still under discussion.

Animals↗
PubMed1975

Tracer and freeze-etching analysis of intra-cellular membrane-junctions in Paramecium with a note on a new heme-nonapeptide tracer.

In paramecia the membranes of alveoli and trichocysts are permanently connected to the cell membrane by membrane-junctions, which consist of membrane-intercalated particles in a regular geometrical arrangement. Trichocysts contain secretory material discharged by exocytosis. In unfixed or fixed cells these two compartments were impermeable to the following tracers: To "microperoxidases", i.e. a cytochrome c-derived heme-nonapeptide and a heme-undecapeptide (WM approximately 1650, 1900) applied in vivo, as well as to lanthanum and cytochrome c used during (La) or after (cytochrome c) fixation. The heme-nonapeptide was prepared by TPCK trypsin digestion of cytochrome c and subsequent purification by Sephadex gel chromatography--a simple and inexpensive new procedure resulting in preparations of high yield and purity. Tracers entered alveoli only when the plasmalemma and the alveolar membranes ruptured upon glutardialdehyde fixation. In no case were transmembraneous channels detectable in regions containing membrane-intercalated particles; this holds true for all tracers used and for freeze-fracture replicas obtained by tantalum-tungsten evaporation. With regard to attachment sites over trichocysts our results do not support the assumptions by others according to which exocytosis would be driven by an osmotic shift via transmembraneous channels (which would be analogous to inter-cellular coupling phenomena mediated by gap-junctions), unless such channels would be assumed to operate as carriers rather than via diffusion. Tracers did not penetrate trichocysts before exocytosis occurred. The functional role of membrane-intercalated particles on trichocyst attachments remains unclear. Despite some resemblance with gap-junctions all types of intra-cellular membrane-junctions investigated are functionally "tight" at the level of "resolution" obtained with tantalumtungsten-shadowing and with the tracers used.

Amino Acid Sequence↗