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991.
Jochen Walz Dieter Typke Michael Nitsch Abraham J. Koster Reiner Hegerl Wolfgang Baumeister 《Journal of structural biology》1997,120(3):387-395
From 3-D reconstructions of automatically recorded tilt series of ice-embedded macromolecules, several hundred 3-D images of single particles can be extracted. Here we describe correlation-based techniques to align the particles with respect to translation and orientation in 3-D and the calculation of an averaged reconstruction after application of the correct weighting function to the particle projections. Multivariate statistical analysis and classification are applied to the set of three-dimensionally reconstructed particles to investigate interimage variations on the 3-D level. 相似文献
992.
Thomas Brinkmann Jochen Schäfers Lutz Gürtler Hiroshi Kido Yasuharu Niwa Nobuhiko Katunuma Harald Tschesche 《The protein journal》1997,16(6):651-660
The serine esterase TL2 from human T4+ lymphocytes is a binding component to HIV-1 glycoprotein gp120 and seems to play a role in the HIV-1 infection mechanism. Recombinant variants of the Kunitz-type serine proteinase inhibitor aprotinin were investigated for their ability to inhibit tryptase TL2 and the binding of gp120 to this enzyme. Furthermore, the viral replication of HIV-1 was investigated in H9 cell cultures under the influence of recombinant aprotinin and bikunin variants. In contrast to native aprotinin, the recombinant variant [Arg15, Phe17, Glu52]aprotinin with a reactive-site sequence homologous to the V3 loop of HIV-1 gp120 showed a specific inhibition of tryptase TL2 (>80%). However, the [Leu15, Phe17, Glu52]aprotinin variant with hydrophobic subsites was the most potent inhibitor of the binding of gp120 to tryptase TL2 (68%). Our results show that the enzyme activity of purified tryptase TL2 is inhibited not only by variants with basic amino acids, but also those with hydrophobic residues in the reactive-site region. Therefore, tryptase TL2 is not a typical trypsin-like or chymotrypsin-like protease. Investigations on inhibition of HIV-1 replication in H9 cell cultures showed that tryptase TL2 is involved in the mechanism of virus internalization into human lymphocytes. The [Leu15, Phe17, Glu52]aprotinin showed a significant retardation of syncytium formation over a period of 5 days in a 1 μM concentration. Similar investigations were performed with recombinant variants of bikunin, the light chain of human inter-α-trypsin inhibitor. Only the single-headed variant [Arg94]82bikunin inhibited slightly the syncytium formation over a period of 2 days in a 2.2 μM concentration. Wild-type bikunin and all full-length variants showed no effect, possibly due to steric hindrance by the second domain of the double-headed inhibitor. 相似文献
993.
Sandra Turconi Jochen Kruip Gerd Schweitzer Matthias Rögner Alfred R. Holzwarth 《Photosynthesis research》1996,49(3):263-268
Picosecond time-resolved fluorescence measurements have been performed as a function of emission wavelengths in order to investigate the possible functional differences between monomeric and trimeric Photosystem I (PS I) particles from a cyanobacterium Synechocystis. Applying global analysis, four kinetic components were found necessary to describe the fluorescecne decay for both monomers and trimers of PS I. The lifetimes and spectra of the respective components are quite similar, indicating that they can be attributed to identical processes in both the monomers and trimers. It is concluded that both forms of PS I are capable of efficient energy transfer and charge separation, in agreement with a physiological role of both forms. Small differences in the fluorescence decays are discussed in terms of a slightly higher ratio of red emitting pigments per reaction centre in trimers of PS I. A comparison to Synechococcus PS I particles reveals the higher red chlorophyll content of the latter.Abbreviations -DM-
-dodecyl-maltoside
- Chl-
chlorophyll
- CMC-
critical micellar concentration
- DAS-
decay-associated spectrum
- DCM-
4-dicyano-methylene-2-methyl-6-(-dimethyl-aminostyryl)-4h-pyran
- FWHM-
full-width at half-maximum
- P700-
primary electron donor of Photosystem I
- PS-
photosystem
- RC-
reaction centre 相似文献
994.
Cellular Expression and Proteolytic Processing of Presenilin Proteins Is Developmentally Regulated During Neuronal Differentiation 总被引:2,自引:0,他引:2
Anja Capell Rainer Saffrich †Jean-Christophe Olivo ‡Liane Meyn Jochen Walter Jürgen Grünberg §Paul Mathews §Ralph Nixon ‡Carlos Dotti Christian Haass 《Journal of neurochemistry》1997,69(6):2432-2440
Abstract: We have determined the expression of the Alzheimer's disease-associated proteins presenilin-1 and presenilin-2 in primary cultures of rat hippocampal neurons. Neurons highly express presenilin-1 and presenilin-2, whereas both proteins were not detected in astrocytes. Further, we have analyzed the subcellular localization and expression in rat hippocampal neurons during development. Although presenilin proteins were localized predominantly to the endoplasmic reticulum in nonneuronal cells transfected with presenilin cDNAs, in neurons, presenilin proteins were also found in compartments not staining with antibodies to grp78(BiP). Presenilin-1 and presenilin-2 were predominantly detected in vesicular structures within the somatodendritic compartment with much less expression in axons. Polarized distribution of presenilin-1 and presenilin-2 differs slightly, with more presenilin-2 expressed in axons compared with presenilin-1. Presenilin expression was found to be developmentally regulated. Presenilin expression strongly increased during neuronal differentiation until full morphological polarization and then declined. No full-length presenilin-1 or presenilin-2 could be detected within cell lysates. At early developmental stages the expected ~34-kDa N-terminal proteolytic fragment of presenilin-1 and the ~38-kDa fragment of presenilin-2 were detected. Later during differentiation we predominantly detected a ~38-kDa fragment for presenilin-1 and a ~42-kDa fragment for presenilin-2. By epitope mapping, we show that these slower migrating peptides represent N-terminal proteolytic fragments, cleaved C-terminal to the conventional site of processing. It is noteworthy that both presenilin-1 and presenilin-2 undergo alternative proteolytic cleavage at the same stage of neuronal differentiation. Regulation of presenilin expression and proteolytic processing might have implications for the pathological as well as the biological function of presenilins during aging in the human brain. 相似文献
995.
Synaptopodin: An Actin-associated Protein in Telencephalic Dendrites and Renal Podocytes 总被引:31,自引:1,他引:30
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Peter Mundel Hans W. Heid Thomas M. Mundel Meike Krüger Jochen Reiser Wilhelm Kriz 《The Journal of cell biology》1997,139(1):193-204
Transforming growth factor-β (TGFβ) is a dimeric peptide growth factor which regulates cellular differentiation and proliferation during development. Most cells secrete TGFβ as a large latent TGFβ complex containing mature TGFβ, latency associated peptide, and latent TGFβ-binding protein (LTBP)-1. The biological role of LTBP-1 in development remains unclear. Using a polyclonal antiserum specific for LTBP-1 (Ab39) and three-dimensional collagen gel culture assay of embryonic heart, we examined the tissue distribution of LTBP-1 and its functional role during the formation of endocardial cushion tissue in the mouse embryonic heart. Mature TGFβ protein was required at the onset of the endothelial-mesenchymal transformation to initiate endocardial cushion tissue formation. Double antibody staining showed that LTBP-1 colocalized with TGFβ1 as an extracellular fibrillar structure surrounding the endocardial cushion mesenchymal cells. Immunogold electronmicroscopy showed that LTBP-1 localized to 40–100 nm extracellular fibrillar structure and 5–10-nm microfibrils. The anti–LTBP-1 antiserum (Ab39) inhibited the endothelial-mesenchymal transformation in atrio-ventricular endocardial cells cocultured with associated myocardium on a three-dimensional collagen gel lattice. This inhibitory effect was reversed by administration of mature TGFβ proteins in culture. These results suggest that LTBP-1 exists as an extracellular fibrillar structure and plays a role in the storage of TGFβ as a large latent TGFβ complex. 相似文献
996.
Titus Kuehne B Kelly Gleason Maythem Saeed Daniel Turner Jochen Weil David F Teitel Charles B Higgins Phillip Moore 《Journal of applied physiology》2005,99(4):1422-1427
This study was conducted to determine the effects of chronic combined pulmonary stenosis and pulmonary insufficiency (PSPI) on right (RV) and left ventricular (LV) function in young, growing swine. Six pigs with combined PSPI were studied, and data were compared with previously published data of animals with isolated pulmonary insufficiency and controls. Indexes of systolic function (stroke volume, ejection fraction, and cardiac functional reserve), myocardial contractility (slope of the end-systolic pressure-volume and change in pressure over time-end-diastolic volume relationship), and diastolic compliance were assessed within 2 days of intervention and 3 mo later. Magnetic resonance imaging was used to quantify pulmonary insufficiency and ventricular volumes. The conductance catheter was used to obtain indexes of the cardiac functional reserve, diastolic compliance, and myocardial contractility from pressure-volume relations acquired at rest and under dobutamine infusion. In the PSPI group, the pulmonary regurgitant fraction was 34.3 +/- 5.8%, the pressure gradient across the site of pulmonary stenosis was 20.9 +/- 20 mmHg, and the average RV peak systolic pressure was 70% systemic at 12 wk follow-up. Biventricular resting cardiac outputs and cardiac functional reserves were significantly limited (P < 0.05), LV diastolic compliance significantly decreased (P < 0.05), but RV myocardial contractility significantly enhanced (P < 0.05) compared with control animals at 3-mo follow-up. In the young, developing heart, chronic combined PSPI impairs biventricular systolic pump function and diastolic compliance but preserves RV myocardial contractility. 相似文献
997.
Zusammenfassung Untersucht wurden einige Pyrenäenseen, die durch ihre Entstehung und ihre trophischen Verhältnisse besonders kennzeichnend sind. Alle gehören zur Gruppe der Hochgebirgsseen, wovon der Lac d'Estaing, entstanden durch Aufstau mittels Schuttkegel, ein natürlicher See ist, während alle übrigen Stauseen darstellen, einesteils an natürliche Seen anknüpfen,, zum anderen durch Aufstau von Flußläufen bedingt.In den Vegetationsverhältnissen ergibt sich eine deutliche Abstufung vom eutrophen Typus (Lac d'Estaing), über schwache Eutrophie-Erscheinungen (Embalse de Terradets) zum rein oligotrophen Typus eines Stausees (z.B. Lac d'Orédon). Alle Seen sind ursprünglich infolge Lage und Klima oligotroph gewesen und erfuhren teilweise durch anthropogene und zoogene Einflüsse eine gewisse Eutrophierung. Ihre Weiterentwicklung wird u.a. abhängen vom Fortfall oder Andauern dieser Einflüsse.
(Aus dem Botanischen Garten und Institut der Universität Köln) 相似文献
Résumé Des recherches ont été faites dans les Pyrénées sur plusieurs lacs particulièrement caractéristiques par leur origine et leurs conditions trophiques. Tous sont des lacs de haute montagne. Le Lac d'Estaing a été formé par refoulement de déblai des montagnes. C'est un lac naturel, tous les autres lacs ont été formés par un refoulement artificiel, d'une part en connection avec un lac naturel et d'autre part par refoulement des cours d'eau. Dans leur végétation il se présente une gradation nettement visible du type eutrophique (Lac d'Estaing), passant par des types mésotrophiques (Embalse de Terradets) au type oligotrophique (Lac d'Orédon). A l'origine tous les lacs étaient oligotrophiques, par suite de leur position géographique et leur climat. Ils sont eutrophiés en partie par des influence anthropogènes et zoogènes. Leur développement ultérieur dépendra de ces infiuences.
(Aus dem Botanischen Garten und Institut der Universität Köln) 相似文献
998.
999.
1000.
The phylogenetic relationships of Przevalski's Finch Urocynchramus pylzowi,the most ancient Tibetan endemic passerine known to date
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Competing systematic hypotheses have placed the Tibetan endemic Przevalski's Finch Urocynchramus pylzowi either with the Old World buntings (Emberizidae) or with the cardueline finches (Fringillidae, Carduelinae). Recent studies based on limited genetic evidence instead suggest an isolated position within Passeroidea and advocate a separate family, Urocynchramidae, as had been suggested much earlier on the grounds of morphology. We provide a time‐calibrated multi‐locus phylogeny for Passeroidea including Przevalski's Finch based on three mitochondrial markers and three nuclear introns that placed U. pylzowi in a clade together with Estrildidae, Viduidae and Ploceidae. A sister group relationship of U. pylzowi and weavers (Ploceidae) was concordant among three multilocus reconstructions but received only poor support. Divergence time estimates inferred from a fossil/biogeographical molecular dating approach suggested a late Oligocene split of U. pylzowi from its closest relatives at roughly 25 million years ago, making this the oldest known Tibetan endemic passerine. In addition to the molecular data, behavioural peculiarities and egg coloration further strengthen an isolated placement of U. pylzowi. 相似文献