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Biomedical subjects

W Dittrich

Publications and source records attributed to W Dittrich.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of TASK-4, a novel member of the pH-sensitive, two-pore domain potassium channel family.

We report the primary sequence of TASK-4, a novel member of the acid-sensitive subfamily of tandem pore K(+) channels. TASK-4 transcripts are widely expressed in humans, with highest levels in liver, lung, pancreas, placenta, aorta and heart. In Xenopus oocytes TASK-4 generated K(+) currents displaying a marked outward rectification which was lost by elevation of extracellular K(+). TASK-4 currents were efficiently blocked by barium (83% inhibition at 2 mM), only weakly inhibited by 1 mM concentrations of quinine, bupivacaine and lidocaine, but not blocked by tetraethylammonium, 4-aminopyridine and Cs(+). TASK-4 was sensitive to extracellular pH, but in contrast to other TASK channels, pH sensitivity was shifted to more alkaline pH. Thus, TASK-4 in concert with other TASK channels might regulate cellular membrane potential over a wide range of extracellular pH.

Amino Acid Sequence↗
PubMed2001

Cytological effects of platelet-derived growth factor on mitochondrial ultrastructure in fibroblasts.

The goal of this study was to evaluate morphofunctional changes in mitochondrial ultrastructure after platelet-derived growth factor application in fibroblasts as an indicator of mitochondrial activation in processes like wound healing. NRK-49F fibroblasts were synchronized, incubated with PDGF (platelet-derived growth factor) and studied by electron microscopy. Volume density (Vv), numerical density (Nv) and surface density (Sv) were measured by stereological analysis. Application of PDGF on NRK-49F caused an increase in mitochondrial volume density by 57% and surface area of cristae per mitochondrion by 65%. The numerical density of the mitochondria was decreased in the PDGF-treated cells by 23%, but at the same time their mean volume was increased. Furthermore, the mitochondria had a complex and highly variable shape both in control and PDGF-treated cells, possibly indicating the existence of a mitochondrial reticulum. The results demonstrated that biochemically active membrane systems in fibroblast mitochondria are enlarged as a direct effect of small doses of platelet-derived growth factor and support the concept that this factor and related peptides serve as mitogens for connective tissue forming cells. Thus, in mitogenic processes like wound healing, the high energy demand of fibroblasts is provided by the increase of the inner surface of mitochondria.

Animals↗
PubMed1997

An in vivo approach for the identification of acceptor sites for O-glycosyltransferases: motifs for the addition of O-GlcNAc in Dictyostelium discoideum.

To identify and analyze acceptor sequences for O-glycosylation, we have developed an in vivo system expressing short peptides as glutathione S-transferase fusion proteins in the eukaryotic host Dictyostelium discoideum. Using this approach, we show that a short peptide motif (PTVTPT), present in the D. discoideum cell-surface glycoprotein PsA, is sufficient as a signal for O-glycosylation, even when fused to a heterologous protein. Monosaccharide analysis and solid-phase protein sequencing showed that the modification is a single N-acetylglucosamine attached to threonine residues. This was further confirmed by electrospray-mass spectrometry. The O-linked glycosylation of both this peptide and authentic PsA presents the modB-dependent carbohydrate-specific epitope identified by the monoclonal antibody MUD50. Substitution of threonine by serine residues in this peptide also yields a glycosylated fusion protein which is modified with single N-acetylglucosamine residues, but not all of the serines are glycosylated.

Acetylglucosamine↗
PubMed1996

DGAP1, a homologue of rasGTPase activating proteins that controls growth, cytokinesis, and development in Dictyostelium discoideum.

A protein accumulated in the cortical region of Dictyostelium discoideum cells proved to be a homologue of GTPase activating proteins that are responsible for the inactivation of ras in yeast and man. Elimination of this protein, DGAP1, by gene replacement resulted in an increased rate of growth of D. discoideum cells on bacterial lawns, and in the formation of aberrant, multi-tipped fruiting bodies. Overexpression of DGAP1 caused the cells to become multi-nucleated since chromosome segregation during mitosis was not reliably followed by cleavage of the cells. These results suggest that in D. discoideum, ras or a related small GTP-binding protein is involved in regulating growth based on the phagocytosis of bacteria, and in coupling activities of the cell cortex to the organization of spindle and asters in mitotic cells.

Amino Acid Sequence↗
PubMed1995

pDcsA vectors for strictly regulated protein synthesis during early development of Dictyostelium discoideum.

Two expression vectors have been constructed to express proteins exclusively in developing cells of Dictyostellium discoideum. In these Escherichia coli/D. discoideum shuttle vectors, proteins are synthesized under control of the promoter of the contact site A (csA) gene, which is efficiently suppressed during growth and becomes strongly activated during early development of D. discoideum. The pDcsA vectors appear to be valuable tools for the production of proteins that are not compatible with growth of D. discoideum cells.

Ampicillin Resistance↗
PubMed1994

Production and secretion of recombinant proteins in Dictyostelium discoideum.

We have expressed useful amounts of three recombinant proteins in a new eukaryotic host/vector system. The cellular slime mold Dictyostelium discoideum efficiently secreted two recombinant products, a soluble form of the normally cell surface associated D. discoideum glycoprotein (PsA) and the heterologous protein glutathione-S-transferase (GST) from Schistosoma japonicum, while the enzyme beta-glucuronidase (GUS) from Escherichia coli was cell associated. Up to 20mg/l of recombinant PsA and 1mg/l of GST were obtained after purification from a standard, peptone based growth medium. The secretion signal peptide was correctly cleaved from the recombinant GST- and PsA-proteins and the expression of recombinant PsA was shown to be stable for at least one hundred generations in the absence of selection.

Amino Acid Sequence↗
PubMed1993

Pretranslational regulation of type I 5'-deiodinase by thyroid hormones and in fasted and diabetic rats.

In both humans and experimental animals, nutritional deprivation and systemic illness are associated with decreases in circulating T3 levels, T3 production, and type I 5'-deiodinase (5'DI) activity. In order to assess the regulation of 5'DI messenger RNA (mRNA) in these conditions, a solution hybridization assay was developed which utilized a complementary (cDNA) encompassing 92% of the 5'DI coding region. The administration of T3 to hypothyroid rats induced a 50-fold increase in 5'DI mRNA levels that preceded by 12 h a similar increase in 5'DI activity. Fasting for 48-72 h, but not 24 h, was associated with an approximate 50% decrease in 5'DI mRNA levels in liver, which preceded a decrease of similar magnitude in 5'DI activity. Fasting in hyperthyroid rats did not lower hepatic 5'DI mRNA levels or activity, nor did fasting attenuate the stimulatory effects of T3 administration on these parameters. In diabetic animals 5'DI mRNA levels and activity were markedly reduced. These results demonstrate that regulation of 5'DI by thyroid hormones and in fasting and diabetes mellitus is exerted principally at the pretranslational level. The relatively late occurrence of decreases in 5'DI mRNA levels and activity observed in nutritional deprivation suggests that these changes are secondary to, rather than causative of, the decreased serum and tissue T3 levels noted in these conditions.

Animals↗
PubMed1992

The unstable tetracycline resistance gene of Streptomyces lividans 1326 encodes a putative protein with similarities to translational elongation factors and Tet(M) and Tet(O) proteins.

Streptomyces lividans contains a genetically unstable tetracycline resistance determinant. Nucleotide sequencing revealed an open reading frame of 1,917 nucleotides. The transcriptional start site was mapped at about 110 bp upstream of the ATG codon. The proposed promoter contains an 8-bp perfect inverted repeat between the -10 and -35 regions. The deduced amino acid sequence showed several motifs which are commonly found in many GTP-binding proteins. On the basis of its amino acid sequence, the presumptive S. lividans 1326 protein belongs to the Tet(M)-Tet(O) group of tetracycline resistance proteins and shows significant similarity to translational elongation factors of prokaryotes and eukaryotes.

Amino Acid Sequence↗
PubMed1991

An amplifiable and deletable chloramphenicol-resistance determinant of Streptomyces lividans 1326 encodes a putative transmembrane protein.

A genetically unstable chloramphenicol resistance gene from Streptomyces lividans 1326 was cloned and characterized. This gene and adjacent DNA regions can be lost spontaneously or amplify within variants. Biochemical studies proved that chloramphenicol is not modified by an acetyltransferase or any other enzyme and that ribosomes of the resistant strain are sensitive to chloramphenicol. Sequence data revealed that the resistance gene encodes a hydrophobic protein predicted to have 12 membrane-spanning alpha-helices and a hydropathic profile similar to the membrane of proteins required for the efflux of tetracycline. Variable proportions of the amino acids (about 16-24%) within the presumed chloramphenicol-resistant protein are identical to various aligned tetracycline-resistant proteins from Gram-negative and Gram-positive bacteria and to transporters for citrate in Klebsiella pneumonaie and for ferrichrome in Escherichia coli.

Amino Acid Sequence↗
PubMed1991

Inactivation of fusidic acid by resistant Streptomyces strains.

Streptomyces lividans and several other Streptomyces species are resistant to the steroid-like antibiotic fusidic acid. This resistance is mediated by structural modification of the antibiotic. Using TLC, CD, UV, IR, NMR and mass spectroscopy the structure of one of the resulting inactive compounds was determined. It is derived from fusidic acid by the loss of an acetyl group and the formation of a lactone ring between C-21 and C-16. In addition, helvolic acid, a compound closely related to fusidic acid, has been shown to be modified.

Chromatography, Thin Layer↗
PubMed1990

Molecular cloning by hybrid arrest of translation in Xenopus laevis oocytes. Identification of a cDNA encoding the type I iodothyronine 5'-deiodinase from rat liver.

The enzyme(s) catalyzing the 5'-monodeiodination of thyroxine and 3,3',5'-triiodothyronine has not yet been purified, and antibodies of demonstrated specificity are not available. Thus, molecular cloning strategies which rely on the traditional screening techniques of using cDNA probes or monospecific antibodies are problematic. We previously reported that expression of type I 5'-deiodinase can be induced in Xenopus laevis oocytes by the injection of poly (A)+ RNA prepared from rat liver (St. Germain, D.L., and Morganelli, C.M. (1989) J. Biol. Chem. 264, 3054-3056). Using this expression system, we developed a hybrid arrest assay, and with it identified a 241-base pair cDNA which encodes part of this enzyme. The cDNA inhibits translation of 5'-deiodinase activity in oocytes by greater than 99% and 5'-deiodinase mRNA from rat liver poly(A)+ RNA in hybrid selection experiments. The cDNA hybridizes to a 1.9-kilobase RNA species on Northern analysis and demonstrates no significant homology to any previously cloned protein. The application of this hybrid arrest strategy for molecular cloning may prove useful for the isolation of cDNAs for proteins that are low in abundance, difficult to purify, or are subunits of a polymeric functional unit.

Animals↗
PubMed1990

Biological properties and partial purification of a growth factor from porcine spleen.

3T3-Fibroblast growth is enhanced in a dose-dependent way by a factor isolated from porcine spleen after limited proteolysis. The factor is not dialyzable and is stable for 5 min at 100 degrees C and at pH 2 at room temperature. Trypsin or collagenase treatment does not affect its biological activity. The stimulation of cell growth is independent of serum concentration in the culture medium but is accelerated by insulin supplement. The biochemical properties of this factor indicate a novel growth promotor different from other growth factors.

Animals↗
PubMed1990

[The bioavailability of doxycycline].

The bioavailability of doxycycline (Doxy-Diolan 100 tablets, test, active substances: 100 mg doxycyclin per tablet) was compared with that of another commercially available tablet-formulation containing the same active substance (reference). In a cross-over study, 16 young healthy male volunteers were administered in fasting state orally by one tablet containing 100 mg active substance. The concentrations of doxycycline were determined in plasma and saliva by a high-performance liquid chromatographic assay. Mean maximum plasma concentration (cmax +/- standard deviation) of doxycycline were 1.57 +/- 0.40 micrograms/ml (test) and 1.59 +/- 0.38 micrograms/ml (reference), respectively, and were reached 1.47 +/- 0.55 h and 1.66 +/- 0.57 h after administration. Plasma half-lives were 16.6 +/- 2.9 h and 16.8 +/- 3.0 h, the areas under the plasma concentration-time curves (AUC0-00) 29.3 +/- 4.5 mg/l.h and 29.7 +/- 4.4 mg/l.h. The concentration of doxycycline in saliva were low, median maximum concentrations of 50 ng/ml were measured 1-2 h after administration. The statistical evaluation revealed bioequivalence between both drugs.

Adult↗
PubMed1989

Learning deficiencies in Borna disease virus-infected but clinically healthy rats.

Borna disease (BD) virus, a still unclassified neurotropic agent, causes either fatal encephalomyelitis or persistent asymptomatic infection in a variety of animal species. We monitored the neuronal functions of intracerebrally infected but healthy rats with three types of learning experiments. Spatial discrimination learning, using the y maze and the hole board, was significantly less successful in BD virus-infected (I) compared with mock-infected (M) rats. Similarly, I rats tended to show a certain emotional disturbance (reduced resting behavior and less anxiety) as evaluated by open-field and neophobia tests. Furthermore, in two aversive learning experiments (taste aversion and reaction suppression via Skinner box), it appeared that the I rats expressed a significantly diminished ability to learn pain avoidance compared with M rats. In conclusion, we found specific learning deficiencies together with subtle behavioral alterations suggesting that BD virus causes certain modulations of high integrative brain functions which are only detectable under experimental conditions.

Animals↗