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D Stock

Publications and source records attributed to D Stock.

At least 37 records · Page 2Linked to original sources
PubMed1995

Crystal structure of the 20S proteasome from the archaeon T. acidophilum at 3.4 A resolution.

The three-dimensional structure of the proteasome from the archaebacterium Thermoplasma acidophilum has been elucidated by x-ray crystallographic analysis by means of isomorphous replacement and cyclic averaging. The atomic model was built and refined to a crystallographic R factor of 22.1 percent. The 673-kilodalton protease complex consists of 14 copies of two different subunits, alpha and beta, forming a barrel-shaped structure of four stacked rings. The two inner rings consist of seven beta subunits each, and the two outer rings consist of seven alpha subunits each. A narrow channel controls access to the three inner compartments. The alpha 7 beta 7 beta 7 alpha 7 subunit assembly has 72-point group symmetry. The structures of the alpha and beta subunits are similar, consisting of a core of two antiparallel beta sheets that is flanked by alpha helices on both sides. The binding of a peptide aldehyde inhibitor marks the active site in the central cavity at the amino termini of the beta subunits and suggests a novel proteolytic mechanism.

Amino Acid Sequence↗
PubMed1995

Proteasome from Thermoplasma acidophilum: a threonine protease.

The catalytic mechanism of the 20S proteasome from the archaebacterium Thermoplasma acidophilum has been analyzed by site-directed mutagenesis of the beta subunit and by inhibitor studies. Deletion of the amino-terminal threonine or its mutation to alanine led to inactivation of the enzyme. Mutation of the residue to serine led to a fully active enzyme, which was over ten times more sensitive to the serine protease inhibitor 3,4-dichloroisocoumarin. In combination with the crystal structure of a proteasome-inhibitor complex, the data show that the nucleophilic attack is mediated by the amino-terminal threonine of processed beta subunits. The conservation pattern of this residue in eukaryotic sequences suggests that at least three of the seven eukaryotic beta-type subunit branches should be proteolytically inactive.

Amino Acid Sequence↗
PubMed1994

Expression, purification and crystallization of human phosphotyrosine phosphatase 1B.

Protein phosphotyrosine phosphatases are believed to be involved in the regulation of the activity of cellular proteins, such as receptor tyrosine kinases, by controlling their phosphorylation status. One of the best described and characterized protein of this class of enzymes is the phosphotyrosine phosphatase 1B. To obtain sufficient quantities for structural investigations, truncated forms of PTP1B encompassing the catalytic domain were over-expressed in Escherichia coli and purified to apparent homogeneity by conventional chromatography. The activity of these purified enzymes has been compared with the wild-type enzyme expressed in mammalian cells. By measuring the activities against p-nitrophenyl phosphate, the pH dependence of this activity, and responses to different modulators, it could be demonstrated that the truncated forms of PTP1B retained the same characteristics as the full-length mammalian enzyme, but are not subject to inhibition of enzymic activity mediated by the C-terminus. Due to their improved solubility, it can be assumed that the catalytic domains are advantageous for crystallization studies in comparison to the natural enzyme. In a screening for crystallization conditions, we obtained protein crystals indicating that the quality of the purified protein is sufficient for crystallographic studies.

Base Sequence↗
PubMed1993

Preliminary X-ray crystallographic study of the proteasome from Thermoplasma acidophilum.

Single cystals of proteasomes from the archaebacterium Thermoplasma acidophilum were obtained using the hanging-drop vapor diffusion method. The crystals diffract to better than 3.0 A and belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions a = 308.9 A, b = 208.8 A and c = 116.9 A. There is one molecular complex in the asymmetric unit. Two potentially useful heavy-atom derivatives have been obtained. The self-rotation function of the native Patterson map shows local sevenfold symmetry, consistent with the low-resolution structure obtained by electron microscopic techniques. The unit cell dimensions and crystal symmetry together with the shape and size of the proteasome suggest a packing arrangement of proteasome molecules in the unit cell, with their cylinder axis nearly parallel to the crystallographic a-axis.

Crystallization↗
PubMed1992

Crystal structure of the factor for inversion stimulation FIS at 2.0 A resolution.

The factor for inversion stimulation (FIS) binds as a homodimeric molecule to a loose 15 nucleotide consensus sequence in DNA. It stimulates DNA-related processes, such as DNA inversion and excision, it activates transcription of tRNA and rRNA genes and it regulates its own synthesis. FIS crystallizes as a homodimer, with 2 x 98 amino acid residues in the asymmetric unit. The crystal structure was determined with multiple isomorphous replacement and refined to an R-factor of 19.2% against all the 12,719 X-ray data (no sigma-cutoff) extending to 2.0 A resolution. The two monomers are related by a non-crystallographic dyad axis. The structure of the dimer is modular, with the first 23 amino acid residues in molecule M1 and the first 24 in molecule M2 disordered and not "seen" in the electron density. The polypeptide folds into four alpha-helices, with alpha A, alpha A' (amino acid residues 26 to 40) and alpha B, alpha B' (49 to 69) forming the core of the FIS dimer, which is stabilized by hydrophobic forces. To the core are attached "classical" helix-turn-helix motifs, alpha C, alpha D (73 to 81 and 84 to 94) and alpha C', alpha D'. The connections linking the helices are structured by two beta-turns for alpha A/alpha B, and alpha C1 type extensions are observed at the C termini of helices alpha B, alpha C and alpha D. Helices alpha D and alpha D' contain 2 x 6 positive charges; they are separated by 24 A and can bind adjacent major grooves in B-type DNA if it is bent 90 degrees. The modular structure of FIS is also reflected by mutation experiments; mutations in the N-terminal part and alpha A interfere with FIS binding to invertases, and mutations in the helix-turn-helix motif interfere with DNA binding.

Amino Acid Sequence↗
PubMed1992

Auditory filter bandwidths as a function of level at low frequencies (125 Hz-1 kHz)

Auditory filter bandwidths were measured using the symmetric notched-noise method in five normally hearing listeners at four masker levels (40-70 dB SPL/Hz in 10-dB steps) and four probe frequencies (125-1000 Hz in octave steps). Accurate stimulus spectrum shape and level were ensured by use of a headphone monitoring technique. Auditory filter bandwidths decreased with decreasing frequency from 1 kHz down to 125 Hz. On the whole, bandwidths increased with increasing level, but the effect of level on bandwidth was greater as frequency increased, with little or no effect of level at 125 Hz. Insofar as the results from the notched-noise method reflect basilar membrane vibration patterns, basilar membrane mechanics appear to become less nonlinear as one approaches the apex of the cochlea.

Adult↗
PubMed1989

Biomechanical considerations on some postoperative problems of directly anchored total hip replacements.

Uncemented total hip replacements have resulted in a higher incidence of postoperative complaints than cemented ones. The theoretical explanation of these not well defined discomforts is based on the differences of the stress and strain fields around the distal portions of the femoral components. While the noncemented stems are press-fitted and most of them tapered distally, thus creating hoop stresses and strains in the surrounding cortical bone, the shrinkage of the cement prevents these mechanical irritations. The relatively sudden disappearance of these discomforts within the first 2 postoperative years is attributed to the shift of the main zone of load transmission from the distal to the proximal portion of the stems following bone remodeling.

Biomechanical Phenomena↗
PubMed1987

NCL-5D3: a new monoclonal antibody recognizing low molecular weight cytokeratins effective for immunohistochemistry using fixed paraffin-embedded tissue.

Production of a new monoclonal antibody designated NCL-5D3 is described. The antibody recognizes several low molecular weight cytokeratins, in particular cytokeratin Moll number 8 as determined by immunoblotting studies, and is highly effective for immunocytochemistry using routinely processed paraffin-embedded material. Staining is enhanced by prior treatment of the sections with trypsin. Assessment using a wide variety of normal and neoplastic tissue indicates reactivity with all tissues of simple or glandular epithelial origin, and in addition with many squamous carcinomas. Thus the antibody should prove of value in diagnostic histopathology.

Antibodies, Monoclonal↗
PubMed1983

[Detection of gamma globulin and Inv markers in vaginal secretions].

The Gm 1, Gm 2, and Inv 1-factors in the vaginal secretion are in accordance with the corresponding serum features to be expected basically. Deviations are possible. They are either caused by interference factors in the vaginal secretion or other factors which are not, however, always detectable in each case. It is important to test in advance the appropriate dilutions for the particular antiserum charges and to examine extracts of the samples to find out whether they have the necessary concentration.

Female↗
PubMed1982

[Detection of hereditary enzyme characteristics in vaginal secretion].

Upon investigation of semen- and blood-free vaginal swabs using starch gel electrophoresis the Phosphoglucomutase type was clearly identified in about 40%. Using cellulose acetate membrane electrophoresis PGM could not be demonstrated. In all cases the results correspond with those obtained in blood. No relation was found between secretor type (determined in saliva) and PGM typing. In vaginal material the following could not be determined: Adenylatkinase (AK) using starch gel electrophoresis, Esterase D (EsD) using cellulose acetate membrane electrophoresis, and Glyoxalase I (GLO) using agarose gel thin-layer electrophoresis.

Adenylate Kinase↗
PubMed1982

The influence of fine surface structures on the osseo-integration of implants.

The availability of inert materials like dense, pure Al2O3-ceramic or titanium allows the study of purely biomechanical influences of surface modulations or lacune on the osseo-integration of implants at different locations of the skeleton. The discovery of the "load-line-shadow" phenomenon in lacune of dental implants and the observation of the same effect in the grooves of hip sockets (Lindenhof type) indicate the general validity of the rules controlling the remodelling ability of bony tissue. Their application to the problems concerned with load transmission via surfaces which are mainly loaded by shear can contribute to achieve a well defined anchorage of implants.

Aluminum Oxide↗
PubMed1980

Results of endoprosthetic hip joint replacement with the aluminum ceramic-metal composite prosthesis "Lindenhof".

The first clinical results of the Lindenhof ceramic-metal composite prosthesis implanted in our hospital in Freiburg are presented. We observed that same favorable early results as the conventional prostheses in a correct position. The implants are incorporated into the bone within 8-12 weeks. The radiographic films show the adaptation of the supporting bone around the ceramic socket. We explain the failures due to our initial lack of technical experience and/or anatomical deformation of the pelvic bone. complications caused by the post-operative treatment during the 12 weeks following surgery did not occur. The combination of a cemented metal femoral component with a ceramic head seems to be a reasonable compromise to use the favorable physical and biochemical properties of the bioceramic material as long as there is no satisfactory solution for a stable cementless fixation of the femoral stem in to the bone. The advantages of the Lindenhof prosthesis predominate the disadvantages: expensive instruments and a post-operative treatment of several months.

Adult↗
PubMed1979

The treatment of osteoarthritis with unconstrained and constrained knee prostheses.

The first cases of knee prosthesis implantation at the orthopaedic department of the Freiburg university hospital are discussed. Surgery was indicated by advanced osteoarthritis which showed no improvement under conservative treatment. Indications concerning the choice of knee joint replacement with unconstrained or constrained prostheses are also discussed. Considerations of these indications as well as operative technique and consequent functional treatment usually produced good results. Follow up studies show equally good results for the GSB-total knee endoprosthesis (constrained) as for the surface type prosthesis (unconstrained).

Female↗
PubMed1977

[The ball deformation method, a new method in oryhopedics for the quantitative threedimensional force flow determination in bone models].

The long term results of 1135 followed up patients after coxarthrosis-operations showed, besides being very effective, typical complications and problems. The bone bearing strength and strain has to be known exactly. In the past there was no method known for quantitative 3dimensional measurement of strength flow in case of biomechanical alteration by operations. The ball deformation system is introduced which was tested on bone models.

Arthritis↗