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C Westphal

Publications and source records attributed to C Westphal.

At least 19 recordsLinked to original sources
PubMed2004

Structural analysis of the SiO2/Si100 interface by means of photoelectron diffraction.

The local environment of Si atoms at the interface between a thermally grown SiO2 film and Si(100) was studied by angle-scanned photoelectron diffraction. Experimental photoelectron diffraction patterns for each Si oxidation state were obtained from the results of least squares fitting on Si 2p core-level spectra. A comparison of the diffraction patterns with multiple-scattering calculations including an R-factor analysis was performed. An excellent agreement between experimental and simulated data was achieved within the proposed bridge-bonded interface model [Phys. Rev. Lett. 84, 4393 (2000)]].

Journal Article↗
PubMed2004

The mammalian mid-pachytene checkpoint: meiotic arrest in spermatocytes with a mutation in Atm alone or in combination with a Trp53 (p53) or Cdkn1a (p21/cip1) mutation.

ATM, the protein product of the gene mutated in the human autosomal recessive disorder ataxia telangiectasia, is involved in detection of double strand breaks (DSBs) and is a key component of the damage surveillance network of cell cycle proteins. In somatic cells ATM phosphorylates many other proteins including p53, an important regulator of cell cycle control. Mice deficient for Atm are male sterile with arrest and apoptosis occurring at testis epithelial stage IV, which in normal spermatocytes corresponds to mid-pachynema. Unlike the situation in somatic cells, we find no evidence that disruption of the Trp53 (p53) gene, or its down-stream target Cdkn1a (p21/Cip1) results in even a partial rescue of the Atm defect.

Animals↗
PubMed2001

Local atomic environment of Si suboxides at the SiO2/Si(111) interface determined by angle-scanned photoelectron diffraction.

Local environments of Si suboxides at the interface between a thermally grown SiO2 film and Si(111) were studied by angle-scanned photoelectron diffraction. Si 2p core-level spectra containing chemically shifted components were recorded. The components were deconvoluted by least squares fitting and assigned to different Si oxidation states. The obtained diffraction patterns of the various suboxides exhibit different features. Comparison of these patterns with multiple scattering calculations including a multipole R-factor analysis shows that a simple chemical abrupt interface model describes well the environment of the suboxides and indicates ordered SiO2 close to the interface.

Journal Article↗
PubMed2000

Characterization of a novel plasmid-encoded HsdS subunit, S.LlaW12I, from Lactococcus lactis W12.

A novel type I restriction-modification specificity subunit, S. LlaW12I, has been identified on the naturally occurring 8.0-kb plasmid pAW122 in the lactic acid bacterium Lactococcus lactis subsp. cremoris W12. Presence of the HsdS protein together with a complete type I restriction-modification system conferred increased phage restriction to the host, indicating exchange of specificity subunits. Sequence analysis showed that the S.LlaW12I subunit is most probably of type IC. Presumably, the hsdS gene is organized together with the repB gene on one transcriptional unit.

Amino Acid Sequence↗
PubMed1995

Studies on the distribution and characteristics of new mammalian selenium-containing proteins.

It has now been established that the essential effects of selenium in mammals are owing to the presence of several biologically active selenium compounds. Seleno-enzymes identified so far include several glutathione peroxidases and the type 1 iodothyronine de-iodinase. Some other selenoproteins have been sequenced and characterized. After in vivo labelling of rats with 75Se and protein separation using gel electrophoretic methods, more than 25 selenium-containing proteins or protein sub-units were detected. Some of the results of the investigations on these compounds are summarized and discussed here. By determining the pattern in a large number of tissues information on the distribution of the selenium-containing proteins was obtained. Their biological significance is not yet known but several findings indicate that some of these proteins may have important functions, especially in the brain and the endocrine and reproductive organs. More detailed information is already available on a 34 kDa-protein found in the testis and spermatozoa. Studies on the effects of dosage and chemical form of dietary selenium indicated that the tissue levels of the seleno-enzymes are homeostatically controlled and cannot be increased by additional supply. The increase in the tissue selenium observed with high selenium intake was found to be mainly caused by the non-specific incorporation of the element into a large number or proteins. The formation of most of the other selenium-containing proteins has priority over that of the cytosolic and plasma glutathione peroxidases. Thus the selenium requirement, which was calculated for optimum plasma glutathione peroxidase activity, also covers the amounts needed for normal levels of the other biologically important selenium compounds.

Animals↗
PubMed1994

Application of nuclear analytical methods in the investigation and identification of new selenoproteins.

Nuclear methods have been applied in the investigation of selenium-containing proteins in rat tissues. Selenium was determined in tissues, cells, and cellular compartments by instrumental neutron activation analysis via 77mSe or 75Se. For tracer studies, the selenium compounds were labeled in vivo by administering 75Se with a high specific activity to rats. Quantitative determination of very small amounts of the element in protein fractions was achieved by measurement of the tracer after replenishment of selenium-depleted animals with the labeled element. The application of the nuclear methods in the detection, characterization, and identification of new selenium-containing proteins is shown with the help of some examples.

Animals↗
PubMed1991

Regulation of expression of genes for milk proteins.

Our results demonstrate that mRNAs that encode two major milk proteins in the mouse, namely, WAP and beta-casein, are found predominantly in the mammary glands of lactating animals. During the course of mammary development from the virgin to the fully lactating animal the steady-state levels of the two RNAs increase about 10(4)-fold, with the most pronounced increase occurring around midpregnancy. Low levels of WAP and beta-casein RNAs are also found in some nonmammary tissues such as tongue, pancreas, and pituitary gland, but not in others, for example, heart and brain. This variation suggests that the transcriptional machinery in some nonmammary cells is capable of recognizing milk-protein genes. The analysis of transgenic animals that carry a hybrid gene composed of the WAP promoter plus the tPA gene strongly suggests that mammary specificity of gene expression is encoded in the promoter/upstream region of the WAP gene. Induction of the genes for WAP and beta-casein during development of mammary glands requires the synergistic action of insulin, hydrocortisone, and prolactin. The increase in levels of the two mRNAs in mammary tissue from midpregnant animals was about 50-fold upon incubation with all three of these hormones, suggesting that no additional hormones may be required in the intact animal. The characteristics of the hormonal induction of the WAP-tPA hybrid gene in transgenic animals differed from those of the induction of the endogenous milk-protein genes in that the presence of all three hormones was not sufficient to increase the levels of the hybrid RNA. This difference suggests that some elements involved in the hormone-dependent accumulation of WAP RNA are located outside the promoter/upstream region, (Pittius et al. 1988a and 1988b). Similar conclusions have been drawn by Groner and coworkers, who analyzed expression of the WAP promoter in two additional hybrid genes (Andres et al. 1988). In addition to the WAP gene, the beta-casein gene also appears to contain hormone-sensitive regulatory elements within the transcribed region. Hybrid genes containing the rat beta-casein promoter (Lee et al. 1989a and 1989b) are expressed in a mammary-specific fashion in transgenic animals but have lost their ability to be regulated by steroid and peptide hormones, a property of their endogenous counterpart.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Melamine resins and their application in electron microscopy.

Melamine resins are derived from the heterocyclic compound triaminotriazine, C3H6N6. Similar to proteins in structure and reactivity, water-soluble melamine resins can be used as water-embedding media for electron microscopy (Bachhuber and Frösch, 1983). The idea behind this approach was to study some of the artefacts of traditional embedding techniques and to work out conditions to eliminate as far as possible denaturing of proteins and extraction of lipids. Sectioned cells and tissues processed in the melamine resin Nanoplast show remarkable preservation of ultrastructure. Because they can be sectioned extremely thinly, melamine resins are particularly suitable for dark-field and electron spectroscopic imaging of unstained molecular suspensions providing in this way an unusually clear reproduction of ultrastructural detail such as the helical structure of isolated unstained double-strand DNA molecules (Frösch et al., 1987b). In 1988, the melamine resin Nanostrat was introduced as an EM-compatible prolific substrate foil for cell culture (Westphal et al., 1988). Cells or bacteria cultivated on this material can be processed for various kinds of follow-up techniques like TEM, SEM, vertical sectioning and immunocytochemistry.

Animals↗
PubMed1989

Integrin VLA-3: ultrastructural localization at cell-cell contact sites of human cell cultures.

The integrin VLA-3 is a cell surface receptor, which binds to fibronectin, laminin, collagen type I and VI (Takada, Y., E. A. Wayner, W. G. Carter, and M. E. Hemler. 1988. J. Cell. Biochem. 37:385-393) and is highly expressed in substrate adherent cultures of almost all human cell types. The ligand specificity of VLA-3 and the inhibition of cell adhesion by anti-VLA-3 monoclonal antibodies suggest its involvement in cell-substrate interaction. In normal tissues, VLA-3 is restricted to few cell types, notably the kidney glomeruli and basal cells of the epidermis. In the epidermis, VLA-3 is generally strongly expressed on the entire plasma membrane of basal cells and is not polarized towards the basement membrane (Klein, C. E., C. Cardon-Cardo, R. Soehnchen, R. J. Cote, H. F. Oettgen, M. Eisinger, and L. J. Old. 1987. J. Invest. Dermatol. 89:500-507). Based on this finding we speculated that, in addition to a role of VLA-3 for adhesion of cells to substrate, it could also be relevant for cell-cell interaction. To investigate this, we ultrastructurally localized VLA-3 on the surface of cultured cells by immunoelectron microscopy. In accordance with our concept, we found VLA-3 strongly associated with intercellular contact sites. Interestingly, very little immunoreactivity was detected at the under-surface of cells which had been cultured for 18-32 h. This observation was unexpected but is consistent with previous findings (Kantor, R. R. S., M. J. Mattes, K. D. Lloyd, L. J. Old, and A. P. Albino. 1987. J. Biol. Chem. 262:15158-15165) which suggest that the association of VLA-3 with the basal surface of substrate adherent tumor cells is a late event occurring after days of culture under confluent conditions. However, we cannot formally rule out VLA-3 expression at the undersurface of cells under our experimental conditions, since VLA-3 molecules at this location could be inaccessible for in situ labeling of unfixed cells because of spatial interferences. In conclusion, our results demonstrate the expression of VLA-3 at intercellular contact sites of cultured cells supporting the concept that it may be relevant for intercellular interactions also.

Animals↗
PubMed1988

A new method for cell culture on an electron-transparent melamine foil suitable for successive LM, TEM and SEM studies of whole cells.

A new cell culture technique is described which is based on the observation that foils cast from the melamine resin hexamethylol-melamine-ether are suitable for the cultivation of beating heart muscle cells and fibroblasts of the rat. This foil can be flamed for sterilization, is about 80 nm in thickness, homogeneous and smooth, withstands dehydration and critical point-drying, can be removed from glass and permits the imaging of whole cells successively by light microscopy, transmission and scanning electron microscopy. The method is capable of narrowing the gap between light and electron microscopy, yielding excellent whole cell preparations in various kinds of microscopic studies to be performed on one and the same cell.

Animals↗
PubMed1987

Dark-field electron microscopy of unstained biological materials embedded in Nanoplast.

Extremely thin sections of unstained materials (beef liver catalase, double-stranded calf thymus DNA, horse spleen ferritin and mammalian skeletal muscle), embedded in the water-soluble melamine resin Nanoplast FB101, were studied by dark-field electron microscopy and electron spectroscopic imaging. While ferritin molecules so recorded show 0.4 and 0.9 nm lattice fringes within the crystalline iron core, double-stranded DNA shows a helical repeat with a spacing of 3.4 nm. The gain in resolution of structural detail reported here is probably due mainly to the reduced section thickness as compared to traditional thin-sectioning techniques. As we reported earlier (Frösch & Westphal, 1984), melamine resins can be sectioned extremely thinly (less than 10 nm) and observed without a supporting film, making them especially suitable for dark-field electron microscopy.

Animals↗