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Biomedical subjects

M Schmid

Publications and source records attributed to M Schmid.

At least 91 records · Page 5Linked to original sources
PubMed2002

Deammonification in biofilm systems: population structure and function.

For the development of alternative concepts for the cost effective treatment of wastewaters with high ammonium content and low C/N-ratio, autotrophic consortia of micro-organisms with the ability to convert ammonium directly into N2 are of particular interest. Several full-scale industrial biofilm plants eliminating nitrogen without carbon source for years in a stable process, are suspected for some time to harbor active anaerobic ammonium oxidizers in deeper, oxygen-limited biofilm layers. In order to identify the processes of the single-stage nitrogen elimination (deammonification) in biofilm systems and to allocate them to the responsible micro-organisms, a deammonifying moving-bed pilot plant was investigated in detail. 15N-labelled tracer compounds were used as well as 16S rDNA libraries and in situ identification of dominant organisms. The usage of rRNA-targeted oligonucleotide probes (FISH) was particularly emphasized on the ammonium oxidizers of the beta-subclass of Proteobacteria and on the members of the order Planctomycetales. The combined application of these methods led to a deeper insight into the population structure and function of a deammonifying biofilm.

Biofilms↗
PubMed2001

Crystallographic structure of ultrathin Fe films on Cu(100).

We report the observation of bcc-like crystal structures in 2-4 monolayer (ML) Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The nonpseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness, is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.

Journal Article↗
PubMed2001

Adsorption sites and ligand effect for CO on an alloy surface: a direct view.

CO adsorption on a PtCo(111) surface was studied by scanning tunneling microscopy. Comparison of images with chemical contrast of Pt and Co and images showing the CO molecules indicates that CO resides exclusively on top of Pt sites and never on Co. CO bonding is highly sensitive to the chemical environment. The probability to find CO on a Pt atom increases drastically with the number of its Co nearest neighbors. Ab initio calculations show that this ligand effect is due to different positions of the center of the Pt d band.

Journal Article↗
PubMed2001

Heterochromatin is not an adequate explanation for close proximity of interphase chromosomes 1--Y, 9--Y, and 16--Y in human spermatozoa.

Analysis of human spermatozoa and lymphocytes using C-banding techniques and in situ hybridization has shown a higher order packaging of the human genome. Chromosomes are not distributed entirely at random within the nucleus. In particular, chromosomes 1, 9, and 16, carrying large blocks of pericentromeric heterochromatin, and the Y chromosome, carrying heterochromatin in Yq12, are in close proximity to each other within the nucleus and are involved in somatic pairing with nonhomologous chromosomes. In order to determine whether the close proximity of these chromosomes in any way is attributable to the distribution of heterochromatin, double in situ hybridization was performed on chromosomes 1--Y, 9--Y, and 16--Y as well as on 1--X, 9--X, and 16--X-with chromosome X as the other gonosome carrying less heterochromatin-in human spermatozoa. Each pair was found to have a nonrandom spatial distribution. However, comparison of the arrangement of chromosomes 1--Y versus 1--X and 9--Y versus 9--X revealed that heterochromatin cannot be the only cause for the tendency of chromosome fusion, because only the results of the chromosome pair 1--Y/1--X could support this proposition. In conclusion, the heterochromatin effect cannot be, in itself, an adequate explanation for chromosome association, implicating as well other mechanisms.

Cell Nucleus↗
PubMed2001

Coupling mechanism of the oxaloacetate decarboxylase Na(+) pump.

The oxaloacetate decarboxylase Na(+) pump consists of subunits alpha, beta and gamma, and contains biotin as the prosthetic group. The peripheral alpha subunit catalyzes the carboxyltransfer from oxaloacetate to the prosthetic biotin group to yield the carboxybiotin enzyme. Subsequently, this is decarboxylated in a Na(+)-dependent reaction by the membrane-bound beta subunit. The decarboxylation is coupled to Na(+) translocation from the cytoplasm into the periplasm, and consumes a periplasmically derived proton. The gamma subunit contains a Zn(2+) metal ion which may be involved in the carboxyltransfer reaction. It is proposed to insert with its N-terminal alpha-helix into the membrane and to form a complex with the alpha subunit with its water-soluble C-terminal domain. The beta subunit consists of nine transmembrane alpha-helices, a segment (IIIa) which inserts from the periplasm into the membrane but does not penetrate it, and connecting hydrophilic loops. The most highly conserved regions of the molecule are segment IIIa and transmembrane helix VIII. Functionally important residues are D203 (segment IIIa), Y229 (helix IV) and N373, G377, S382 and R389 (helix VIII). The polar of these amino acids may constitute a network of ionizable groups which promotes the translocation of Na(+) and the oppositely oriented translocation of H(+) across the membrane. Evidence indicates that two Na(+) ions are bound simultaneously to subunit beta with D203 and S382 acting as binding sites. Sodium ion binding from the cytoplasm to both sites elicits decarboxylation of carboxybiotin possibly with the consumption of the proton extracted from S382 and delivered via Y229 to the carboxylated prosthetic group. A conformational change exposes the bound Na(+) ions toward the periplasm. With H(+) entering from the periplasm, the hydroxyl group of S382 is regenerated, and as a consequence, the Na(+) ions are released into this compartment. After switching back to the original conformation, Na(+) pumping continues.

Amino Acid Sequence↗
PubMed2001

Kinetically assisted potential sputtering of insulators by highly charged ions.

A new form of potential sputtering has been found for impact of slow ( < or = 1500 eV) multiply charged Xe ions (charge states up to q = 25) on MgO(x). In contrast to alkali-halide or SiO2 surfaces this mechanism requires the simultaneous presence of electronic excitation of the target material and of a kinetically formed collision cascade within the target in order to initiate the sputtering process. This kinetically assisted potential sputtering mechanism has been identified to be present for other insulating surfaces as well.

Journal Article↗
PubMed2001

The ricinosomes of senescing plant tissue bud from the endoplasmic reticulum.

The ricinosome (synonym, precursor protease vesicle) is a novel organelle, found so far exclusively in plant cells. Electron microscopic studies suggest that it buds off from the endoplasmic reticulum in senescing tissues. Biochemical support for this unusual origin now comes from the composition of the purified organelle, which contains large amounts of a 45-kDa cysteine endoprotease precursor with a C-terminal KDEL motif and the endoplasmic reticulum lumen residents BiP (binding protein) and protein disulfide isomerase. Western blot analysis, peptide sequencing, and mass spectrometry demonstrate retention of KDEL in the protease proform. Acidification of isolated ricinosomes causes castor bean cysteine endopeptidase activation, with cleavage of the N-terminal propeptide and the C-terminal KDEL motif. We propose that ricinosomes accumulate during senescence by programmed cell death and are activated by release of protons from acidic vacuoles.

Amino Acid Sequence↗
PubMed2001

Influence of impurities on localized transition metal surface states: scanning tunneling spectroscopy on V(001).

The first scanning tunneling spectroscopy measurements on V(001) are reported. A strong surface state is detected which is very sensitive to the presence of segregated carbon impurities. The surface state energy shifts from 0.03 eV below the Fermi level at clean areas towards higher energies (up to approximately 0.2 eV) at contaminated areas. Because of the negative dispersion of this state, the upward shift cannot be described in a simple confinement picture. Rather, the surface state energy is governed by vanadium surface s- d interactions which are altered by carbon coverage.

Journal Article↗
PubMed2001

Nucleation of bcc iron in ultrathin fcc films.

Needle-shaped bcc nucleation centers in fcc films of Fe on Cu(100) are observed by scanning tunneling microscopy. They form virtually without mass transfer and nearly under conservation of volume, which causes a large strain within the nascent bcc grain. The corresponding strain energy almost equals the gain in structural energy, rendering the bcc nucleation very sensitive to any effect influencing this subtle balance. We suggest that modifying the film by straining, alloying, or surface adsorption may inhibit the bcc nucleation and lead to thick metastable fcc films.

Journal Article↗
PubMed2001

Characterization of murine BATF: a negative regulator of activator protein-1 activity in the thymus.

BATF belongs to the AP-1/ATF superfamily of transcription factors and forms heterodimers with Jun proteins to bind AP-1 consensus DNA. Unlike Fos/Jun heterodimers which stimulate gene transcription, BATF/Jun heterodimers are transcriptionally inert and inhibit biological processes that are associated with the overstimulation of AP-1 activity. Here, we describe the murine BATF cDNA and genomic clones and map the BATF locus to chromosome 12 D2-3. Using in situ hybridization of BATF mRNA, we show that BATF gene expression is highly restricted, with the most prominent signals detected in the thymus. BATF mRNA levels are regulated differentially during discrete stages of T cell development and are up-regulated following activation of T cells in the periphery. To demonstrate the impact of BATF on AP-1 activity in vivo, AP-1 luciferase reporter mice were crossed to transgenic mice overexpressing BATF exclusively in thymic T cells. Results show that elevated levels of BATF protein correlate with reduced transactivation by AP-1. Since the differential regulation of AP-1 activity is linked to key transitions in the developing immune system, our observations support a critical role for BATF in determining the overall level of AP-1 activity, and thus AP-1 target gene expression, in specific T cell subtypes.

Amino Acid Sequence↗
PubMed2001

Enantioselective high-performance liquid chromatography of therapeutically relevant aminoalcohols as their fluorescent 1-naphthyl isocyanate derivatives.

A method for determining the enantiomers of 10 therapeutically relevant aminoalcohols using HPLC and precolumn derivatization was developed. Naphthyl isocyanate reacted with racemic aminoalcohols to form urea derivatives which were separated isocratically on a cellulose tris(3,5-dimethylphenylcarbamate) coated silica gel column, and detected fluorometrically in the lower ng mL(-1) range. The effluents can also be monitored at lower sensitivity, using an ultraviolet detector operated at 220 nm.

Amino Alcohols↗
PubMed2001

3D contrast-enhanced MR angiography of the run-off vessels: value of image subtraction.

The diagnostic gain associated with image subtractions was assessed regarding contrast-enhanced 3D magnetic resonance angiography (MRA) image sets of the pelvic and lower extremity arteries. The MRA strategy combined a dedicated vascular coil with a single injection, two-station protocol. Voxel-by-voxel signal intensity subtraction was performed on MRA image sets obtained before and during dynamic infusion of a para-magnetic contrast agent. Non-subtracted and subtracted MRA image sets were assessed for the presence of occlusive (four grades) disease, using DSA as the standard of reference. In addition, SNR and CNR were recorded for each vascular segment on both the non-subtracted and subtracted images. While CNR values of subtracted images exceeded those of non-subtracted images (P < 0.05), there was no difference in diagnostic performance. For the detection of hemodynamically significant disease, non-subtracted and subtracted MRA provided overall sensitivity and specificity of 90.2%/90.3% and 95.1%/95.6%, respectively. Concordance between non-subtracted and subtracted MRA was excellent (Kappa = 0.86).

Aged↗
PubMed2001

Genomic organization and expression of the doublesex-related gene cluster in vertebrates and detection of putative regulatory regions for DMRT1.

Genes related to the Drosophila melanogaster doublesex and Caenorhabditis elegans mab-3 genes are conserved in human. They are identified by a DNA-binding homology motif, the DM domain, and constitute a gene family (DMRTs). Unlike the invertebrate genes, whose role in the sex-determination process is essentially understood, the function of the different vertebrate DMRT genes is not as clear. Evidence has accumulated for the involvement of DMRT1 in male sex determination and differentiation. DMRT2 (known as terra in zebrafish) seems to be a critical factor for somitogenesis. To contribute to a better understanding of the function of this important gene family, we have analyzed DMRT1, DMRT2, and DMRT3 from the genome model organism Fugu rubripes and the medakafish, a complementary model organism for genetics and functional studies. We found conservation of synteny of human chromosome 9 in F. rubripes and an identical gene cluster organization of the DMRTs in both fish. Although expression analysis and gene linkage mapping in medaka exclude a function for any of the three genes in the primary step of male sex determination, comparison of F. rubripes and human sequences uncovered three putative regulatory regions that might have a role in more downstream events of sex determination and human XY sex reversal.

Amino Acid Sequence↗
PubMed2001

Sex chromosomes, sex-linked genes, and sex determination in the vertebrate class amphibia.

In this chapter the different categories of homomorphic and heteromorphic sex chromosomes, types of sex-determining mechanisms, known sex-linked genes, and data about sex-determining genes in the Amphibia have been compiled. Thorough cytogenetic analyses have shown that both XY/XX and ZW/ZZ sex chromosomes exist in the order Anura and Urodela. In some species quite unusual systems of sex determination have evolved (e.g. 0W-females/00-males or the co-existence of XY/XX and ZW/ZZ sex chromosomes within the same species). In the third order of the Amphibia, the Gymnophiona (or Apoda) there is still no information regarding any aspect of sex determination. Whereas most species of Anura and Urodela present undifferentiated, homomorphic sex chromosomes, there is also a considerable number of species in which an increasing structural complexity of the Y and W chromosomes exists. In various cases, the morphological differentiation of the sex chromosomes occurred as a result of quantitative and/or qualitative changes to the repetitive DNA sequences in the constitutive heterochromatin of the Y and W chromosomes. The greater the structural differences between the sex chromosomes, the lesser the extent of pairing in meiosis. No dosage compensation of the sex-linked genes in the somatic cells of the homogametic (XX or ZZ) individuals have been detected. The genes located to date on the amphibian sex chromosomes lead to the conclusion that there is no common ancestral or conserved sex-linkage group. In all amphibians, genetic sex determination (GSD) seems to operate, although environmental factors may influence sex determination and differentiation. Despite the accumulated evidence that GSD is operating in Anura and Urodela, there is little substantial information about how it functions. Although several DNA sequences homologous to the mammalian ZFY, SRY and SOX genes have been detected in the Anura or Urodela, none of these genes is an appropriate candidate to explain sex determination in these vertebrates.

Amphibians↗
PubMed2001

Ricinosomes: an organelle for developmentally regulated programmed cell death in senescing plant tissues.

This review describes aspects of programmed cell death (PCD). Present research maps the enzymes involved and explores the signal transduction pathways involved in their synthesis. A special organelle (the ricinosome) has been discovered in the senescing endosperm of germinating castor beans (Ricinus communis) that develops at the beginning of PCD and delivers large amounts of a papain-type cysteine endopeptidase (CysEP) in the final stages of cellular disintegration. Castor beans store oil and proteins in a living endosperm surrounding the cotyledons. These stores are mobilized during germination and transferred into the cotyledons. PCD is initiated after this transfer is complete. The CysEP is synthesized in the lumen of the endoplasmic reticulum (ER) where it is retained by its C-terminal KDEL peptide as a rather inactive pro-enzyme. Large number of ricinosomes bud from the ER at the same time as the nuclear DNA is characteristically fragmented during PCD. The mitochondria, glyoxysomes and ribosomes are degraded in autophagic vacuoles, while the endopeptidase is activated by removal of the propeptide and the KDEL tail and enters the cytosol. The endosperm dries and detaches from the cotyledons. A homologous KDEL-tailed cysteine endopeptidase has been found in several senescing tissues; it has been localized in ricinosomes of withering day-lily petals and dying seed coats. Three genes for a KDEL-tailed cysteine endopeptidase have been identified in Arabidopsis. One is expressed in senescing ovules, the second in the vascular vessels and the third in maturing siliques. These genes open the way to exploring PCD in plants.

Apoptosis↗
PubMed2001

Genomic plasticity and melanoma formation in the fish Xiphophorus.

Melanoma formation in certain interspecific hybrids of the genus Xiphophorus (Teleostei: Poeciliidae) is associated with the overexpression of the Xmrk receptor tyrosine kinase oncogene. The Xmrk oncogene arose by duplication of the pre-existing Xmrk protooncogene in a highly unstable subtelomeric region of the X and Y sex chromosomes undergoing frequent rearrangements including duplications, deletions, amplifications, and transpositions. Some of these rearrangements are likely to be responsible for the overexpression of the Xmrk oncogene in melanoma. The oncogene itself is very unstable in Xiphophorus and is frequently removed by deletion or disrupted by transposable elements. The Xmrk oncogene region displays a high concentration of retroelements not observed in the corresponding Xmrk protooncogene region. Particularly, a retrovirus long terminal repeat-like sequence was amplified in the proximity of the Xmrk oncogene. Additional genes, some of them also duplicated copies, were detected in this region and might be involved in modulating the melanoma's phenotype.

Journal Article↗
PubMed2001

Ribozyme-mediated cleavage of wt1 transcripts suppresses growth of leukemia cells.

OBJECTIVE: The Wilms' tumor gene product (WT1) was identified as a tumor suppressor in pediatric kidney tumors. Conversely, acute leukemias express WT1 at a high frequency, and leukemias with high levels of WT1 expressed by leukemic blast cells have a significantly worse prognosis, suggesting an oncogenic function of WT1 in leukemic cells. To address this issue, we developed five hammerhead ribozymes (RZ1-RZ5) designed to cleave various wt1-mRNA GUC-recognition sites and thus suppress wt1 expression. METHODS: Using in vitro transcribed ribozymes and truncated wt1 target RNAs as substrates, we performed in vitro cleavage assays. The sequence of two ribozymes was then cloned into the pCDNA3 expression vector containing a self-processing ribozyme cassette. Downregulation of wt1 due to ribozyme expression was analyzed in the human 293 embryonic kidney and the K562 chronic myeloid leukemia cell line by Western blotting and RT-PCR. Growth of stable transfected K562 cells was determined by proliferation analysis and 3H-thymidine incorporation. RESULTS: In vitro, the anti-wt1 ribozymes were able to recognize and cleave the target RNA in a highly sequence-specific and time-dependent manner. The ribozymes showed different catalytic activity. Coexpression of wt1 and the self-processing ribozymes pRZ3 and pRZ5, respectively, resulted in a significantly downregulated WT1 protein level when transiently transfected in 293 cells. Furthermore, stable transfection of pRZ3 and pRZ5 resulted in considerably reduced expression of endogenous wt1 in K562 cells, correlating with the inhibition of cell proliferation and the induction of cell death. CONCLUSION: Our data suggest that anti-wt1 ribozymes are a potent inhibitor of wt1 expression with possible implications for the inhibition of cell proliferation in leukemic cells.

Base Sequence↗