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D Kamp

Publications and source records attributed to D Kamp.

At least 19 recordsLinked to original sources
PubMed1996

Pathways for flip-flop of mono- and di-anionic phospholipids in the erythrocyte membrane.

The inward translocations (flip), from the outer to the inner membrane leaflet of human erythrocytes, of di-anionic NBD-labeled phospholipids containing as a head group phosphate esters of glycolate, butyrate and hydroxyethanesulfonate are slow processes (k = 0.005-0.008 h-1, 37 degrees C) at pH 7.4. A decrease of pH highly stimulates the flip. A major role of the anion exchanger (AE1), band 3, in this flip is indicated by (a) the strong inhibition of the flip (55-85%) by stilbene disulfonates and other inhibitors of anion transport, (b) the stimulation and loss of pH dependence of the flip after modification of band 3 by Woodward's reagent K and NaBH4, and (c) the stimulation of the flip after proteolytic cleavage of band 3 by papain. The flip of mono-anionic NBD-phospholipids with phosphate esters of glycerol, glycol, methanol, butanol and benzyl alcohol is much faster than that of their dianionic analogs (k = 0.04 to > 3.0 h-1, 37 degrees C). It is inhibited by stilbene disulfonates to a decreasing extent (35 to 0%) and is not affected by several reversible inhibitors of anion exchange. This indicates a minor component of band-3-mediated flip and a major component of nonmediated flip. The outward translocations (flop), from the inner to outer membrane leaflet, of both mono- and di-anionic phospholipids are very fast (1.0-5.9 h-1), ATP-dependent and inhibitable by vanadate, fluoride, SH-reagents or Mg(2+)-depletion of cells and thereby likely to be largely mediated by a 'floppase'. The stationary distributions of the NBD-labeled anionic phospholipids are asymmetric to an extent (outer to inner leaflet ratio 2-9) correlating with the ratio of the rates of the outward and the inward translocation. Thus, asymmetry is largely abolished by blockage of the floppase-mediated translocation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Conserved sequence patterns in phages Mu and lambda DNA.

The genetic maps of bacteriophages Mu and lambda can be aligned with respect to the functions of their genes. We were interested to ascertain whether the congruence of gene order is reflected at the nucleotide sequence level. A sliding window analysis of sequences from the early regions of both phages revealed a substantial degree of similarity. Equally high scores, however, were found when the early region of Mu was compared to the late region of lambda and in self-comparisons of either Mu or lambda. Hence, the similarity is due to a common pattern of nucleotides rather than to sequence similarities between functionally related genes. Employing degenerated scoring matrices we could show that primarily adenine and thymine residues contribute to the high scores and that a specific clustering of these residues is the basis for the conserved pattern. Since such a similarity was not observed with control sequences of other phages. Escherichia coli or eukaryotic viruses, the data support the notion that Mu and lambda have diverged from a common phage module. In general, our approach could offer a simple and sensitive way to trace distant relationships.

Bacteriophage lambda↗
PubMed1994

Classification of genetic sequences with backpropagation.

A backpropagation algorithm is used to train a neural net with the goal of distinguishing between two groups of biological species: prokaryotic and eukaryotic, based on frequencies of all 16 doublets in DNA sequences. An improvement of about 15% is obtained compared to statistical analysis based on one doublet only. This is done first by presenting sequences of species to the network with known classification (the training phase) and then showing species which the neural net has never seen before, and looking for the response. A brief discussion of the speed of training is given.

Algorithms↗
PubMed1992

An in vitro investigation of the action of lamotrigine on neuronal voltage-activated sodium channels.

Lamotrigine (LTG), 6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine, is a novel antiepieptic drug structurally unrelated to the major anticonvulsants in current use. Previous studies of LTG in rodents revealed efficacy in maximal electroshock test, pentylenetetrazol test and kindling models of seizures suggesting potential utility in the treatment of partial and generalized (tonic-clonic) seizures. In the present study, LTG was found to block sustained repetitive firing of sodium-dependent action potentials in mouse spinal cord cultured neurons and inhibit [3H]batrachotoxinin A 20-alpha-benzoate binding in rat brain synaptosomes suggesting a direct interaction with voltage-activated sodium channels.

Action Potentials↗
PubMed1990

The sequence of the hemoregulatory peptide is present in Gi alpha proteins.

The hemoregulatory peptide PyroGlu-Glu-Asp-Cys-Lys (HP5b), which inhibits myelopoietic colony formation in vitro, is shown to be a sequence motif which is also part of the effector domain of Gi alpha proteins. Out of 8 synthetic peptides with sequence variations of HP5b, those with the closest similarity to the Gi alpha sequence are biologically active. The inhibitory effect appears to be dependent on the blocked N-terminus. It is postulated that these peptides may interfere with signal transduction mediated by Gi alpha proteins.

Amino Acid Sequence↗
PubMed1989

Evolution of the DNA invertase Gin of phage Mu and related site-specific recombination proteins.

The relationship between site-specific recombination enzymes has been studied by computer analysis of nucleotide and amino acid sequences. A phylogenetic tree for two types of these enzymes has been constructed. DNA resolvases of Tn3-related transposable elements and DNA invertases form a superfamily which can be divided into four families of resolvases and one family of invertases comprising the Gin, Cin, Pin and Hin proteins. The DNA invertase genes descend from the tnpR branch that is represented by Tn917. Although TnpR 917 and Gin are almost 50% identical in their amino acid sequence, no gin-complementing activity of Tn917 could be measured. Within the family of DNA invertases, Gin and Pin are the closest relatives. The degree of sequence relatedness of the various invertases compared to Gin correlates with the biological relatedness tested in a gin complementation assay. A relationship between the inversion enzymes FimB and FimE and the super-family of site-specific recombinases could not be detected by these methods.

Bacteriophages↗
PubMed1988

The immunological profile of a new immunomodulatory agent, oxamisole.

Oxamisole is a T-cell immunorestorative agent when administered by the oral (p.o.) route. It has little or no effect on the IgM or IgG responses to the T-dependent antigen, sheep erythrocytes (SRBC), in normal mice but augments antibody production in immunodeficient animals. Unlike the response to SRBC, the humoral immunocompetence of both normal and immunosuppressed animals sensitized with the T-independent antigen, trinitrophenyl-lipopolysaccharide (TNP-LPS) was unaffected by oxamisole. Oxamisole restored cellular immunocompetence, as evidenced by an increase in the in vitro proliferative response of normal murine splenocytes to T-cell mitogens, while decreasing B-cell mitogenic responses. This indicates that oxamisole may selectively restore T-cell function. However, oxamisole did not significantly modify the classical T-cell-mediated delayed hypersensitivity responses to either the protein antigen methylated bovine serum albumin or to the contact-sensitizing antigen oxazolone. When assayed in vitro, oxamisole enhanced macrophage chemotactic function but not phagocytic function, suggesting a potential stimulation of the reticuloendothelial system. In vivo studies failed to demonstrate any consistent significant activation of murine macrophage function following oral dosing with oxamisole.

Adjuvants, Immunologic↗
PubMed1986

Mu-induced rifamycin-resistant mutations not located in the rpoB gene of Escherichia coli.

A new class of rifamycin-resistant mutants of Escherichia coli was obtained by lysogenic insertions of bacteriophage Mu Amp DNA. Rifamycin resistance is closely linked to the ampicillin resistance conferred by the prophage. Mapping by conjugation with auxotrophic markers revealed that the rifamycin-resistant mutations are located between 28 and 37 min on the E. coli chromosome standard map, some distance from the rpoB gene at 89.5 min. The DNA-dependent RNA polymerase of these mutants is highly sensitive to rifampicin.

Coliphages↗
PubMed1986

DNA inversion in bacteriophage Mu: characterization of the inversion site.

Gin-mediated site-specific recombination promotes inversion of the G segment of phage Mu. The crossover takes place between two 34 bp-long inverted repeat sequences flanking the G segment. We have characterized the inversion site, the target for the site-specific recombination mechanism. An artificial invertible segment was constructed which consists of parts of the invertible segments of Mu and phage P1, which in this respect are largely homologous. Upon inversion of this hybrid segment the crossover site could be located, by DNA sequencing, in the ACCT sequence of the centre of symmetry in the inverted repeat in Mu. The hybrid Mu-P1 segment inverts at a lower frequency than its parental invertible segments probably because of the mismatches between the inverted repeats of Mu and P1. This suggests that base pairing between the inverted repeats is an intermediate step in recombination. Plasmids with subcloned G segments lacking the adjacent beta region of Mu or the corresponding region in P7, a relative of P1, are deficient in inversion. By analysis through site-specific mutagenesis of Mu DNA, an enhancer element with multiple recognition sites was identified which is necessary for efficient inversion. This component of the inversion site was located in a 170 bp segment within the Mu beta region, 30 bp to the right of the inverted repeat sequence, but can be separated from the crossover site by a 1200 bp insertion without losing its effect.

Bacteriophage mu↗
PubMed1984

Application of high-performance liquid chromatographic techniques to the separation of ribosomal proteins of different organisms.

The ribosomal proteins from Escherichia coli, Bacillus stearothermophilus and Methanococcus vannielii were separated by size-exclusion, ion-exchange and reversed-phase high-performance liquid chromatography (HPLC), employing new column materials, different gradient systems, and preparative columns, respectively. The purity of the isolated proteins was analysed by one- and two-dimensional gel electrophoresis and by direct micro-sequencing. The separation of ribosomal proteins could be improved by employing propanol gradients in combination with Vydac reversed-phase columns. From the E. coli ribosome, fifteen S and twenty-three L proteins were isolated in sequencer purity by this method. In addition, ion-exchange HPLC was proven to be useful for isolating ribosomal proteins under native conditions: six S proteins and sixteen L proteins from E. coli could be purified. Some of these proteins were not isolated by the reversed-phase procedures, e.g. proteins L9, L14 and L21.

Amino Acid Sequence↗
PubMed1984

Cell wall receptor for bacteriophage Mu G(+).

The invertible G segment in phage Mu DNA controls the host range of the phage. Depending on the orientation of the G segment, two types of phage particles, G(+) and G(-), are produced which recognize different cell surface receptors. The receptor for Mu G(+) was located in the lipopolysaccharide (LPS) of gram-negative bacteria. The analysis of different LPS core types and of mutants that were made resistant to Mu G(+) shows that the primary receptor site on Escherichia coli K-12 lies in the GlcNAc beta 1 . . . 6Glc alpha 1-2Glc alpha 1-part at the outer end of the LPS. Mu shares this receptor site in E. coli K-12 with the unrelated single-stranded DNA phage St-1. Phage D108, which is related to Mu, and phages P1 and P7, which are unrelated to Mu but contain a homologous invertible DNA segment, have different receptor requirements. Since they also bind to terminal glucose in a different configuration, they adsorb to and infect E. coli K-12 strains with an incomplete LPS core.

Coliphages↗
PubMed1982

Capillary resistance to flow of hardened (diamide treated)red blood cells (RBC).

Pressure-flow curves for control and hardened (diamide treated) human RBC's were obtained in capillaries of the isolated rat mesentery, in order to evaluate resistance to flow of hardened RBC's. Blood vessels were maximally dilated by an infusion of 10(-5) mol/l acetylcholine and isoprenaline and perfused with freshly collected human RBC's as well as with RBC's hardened by a treatment (hct 40%; pH 8.0; 37 degree C) with 0.5 mmol/l or 1.5 mmol/l diamide, respectively, suspended in Albumin (0.05%) - Ringer solution. The mesentery was perfused via a hydrostatic pressure reservoir. Arterio-venous pressure difference was varied from 4-10 kPa, and corresponding arteriolo-venular pressure gradients changed from about 200-500 Pa/mm. No significant difference in resistance to flow was observed between control and diamide treated cells over the whole pressure range. However, the flow through the microvascular bed was inhomogeneous upon perfusion with diamide treated cells, caused by a deceleration and stoppage of the cells at capillary narrowing (ratio of cell to vessel diameter greater than 2). The time of stagnation increased with decreasing pressure gradient.

Animals↗
PubMed1982

Nucleotide sequence of the immunity region of bacteriophage Mu.

The leftmost 1590 bp of Mu DNA covering the immunity region have been sequenced. This region encodes the cI repressor, the cII or ner function and the beginning of gene A. An open reading frame extends from position 863 to 342 on the l-strand corresponding to cI protein with a molecular weight of 19212. It is preceded by a sequence resembling a promoter. To the right of the HindIII site an open reading frame extends from position 1099 to 1323 corresponding to cII or ner protein (molecular weight of 8505) followed by the beginning of gene A at position 1328. Between position 863 and 1099 promoters for leftward and rightward transcription and operator-like structures can be recognized in the sequence. The promoter for rightward transcription overlaps with the HindIII site and coincides with a RNA polymerase binding site as demonstrated by electron microscopy.

Bacteriophage mu↗
PubMed1981

Topology of membrane sulfhydryl groups in the human erythrocyte. Demonstration of a non-reactive population in intrinsic proteins.

A major fraction of the protein sulfhydryl groups of human erythrocyte membranes can be oxidized to disulfide bonds by the lipid soluble reagent, diamide, and the hydrophilic reagent, tetrathionate. Furthermore, the same fraction also reacts with the monofunctional reagent, N-ethylmaleimide. About 20% of the SH groups, however, do not react with any of these agents even upon prolonged treatment and increased concentrations. These 'non-reacting' SH groups were now localized by a procedure involving blockage of the accessible SH groups by non-labeled N-ethylmaleimide or by diamide, subsequent isolation and solubilization of the membranes in SDS and labelling of the now accessible, residual SH groups with N-[ethyl-2-3H]ethylmaleimide. The distribution of the radioactivity over the peptide fractions shows that the non-reacting SH groups are mainly localized in the intrinsic proteins, while essentially all of the SH groups of the extrinsic protein, spectrin, are reactive. After solubilization of the membranes with Triton X-100 the non-reacting SH groups became reactive towards N-ethylmaleimide. It is proposed that lack of reaction of SH groups in the native membranes is due to their localization within the hydrophobic core of the membrane.

Erythrocyte Membrane↗