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F Wohlrab

Publications and source records attributed to F Wohlrab.

At least 19 recordsLinked to original sources
PubMed1992

GC-rich flanking tracts decrease the kinetics of intramolecular DNA triplex formation.

The effect of the base composition of flanking sequences on DNA intramolecular triplex formation was investigated in negatively supercoiled plasmids. The rates of triplex formation at two oligopurine.oligopyrimidine inserts with interrupting sequences in plasmids containing AT- or GC-rich flanking sequences were compared as a function of temperature, pH, and negative superhelical density. The kinetics of the transition of linear B-DNA to triplex (also called H-DNA) were influenced by all of these factors; triplexes were formed slower in a GC-rich background than in an AT-rich background. However, at equilibrium, the same amounts of the triplexes in AT- or GC-rich contexts were formed, and the conformations adopted by (GAA)4TTCGC(GAA)4 showed the canonical intramolecular triplex as mapped with chemical probes. We propose that the GC-rich segments caused this effect by thermodynamically clamping the DNA inserts, since the dependence of kinetics on base composition disappeared in tetraalkylammonium ions which eliminate the dependence of helix-coil transitions on base composition. The dependence of the kinetics of intramolecular triplex formation on flanking sequences further strengthens the concept of the role of DNA as a dynamic participant in cellular events.

Base Sequence↗
PubMed1992

Metal ions cause the isomerization of certain intramolecular triplexes.

The influence of cations on the capacity of five oligopurine.oligopyrimidine mirror repeat sequences to adopt intramolecular triplexes (the usual H-y3 isomer and/or the rare H-y5 isomer) in recombinant plasmids was investigated. Unexpectedly, the presence of certain metal ions (magnesium, zinc, manganese, and calcium) stabilized the (GAA)4TTCGC(GAA)4 insert in the rare H-y5 when cloned into either of two different sequence backgrounds. Alternatively, either shortening or lengthening the sequence at the central interruption, which becomes the loop of the triplex, led to the formation of the canonical H-y3 under all conditions tested. Similarly, other oligopurine.oligopyrimidine mirror repeat sequences (i.e. (GAA)8 or (GGA)8) formed only the H-y3 under all experimental conditions. All triplexes were stabilized by negative supercoiling at pH 5.0; chemical probe and primer extension analyses served as critical structural tools. Hence, the nature of the central interruption sequence (the loop) of the mirror repeat is important for the stabilization of the H-y5. This region may be important for metal ion binding in the initial stages of triplex formation and thus may play a critical role in determining which isomer is formed. The possible biological role of a DNA sequence adopting three different conformations is discussed.

Cations↗
PubMed1991

The herpes simplex virus 1 segment inversion site is specifically cleaved by a virus-induced nuclear endonuclease.

Nuclear extracts from several tissue culture cell lines (human, primate, and murine) contain an endonuclease that specifically cleaves sequences at the herpes simplex virus 1 (HSV-1) segment inversion site. Mapping studies identified the preferential site of cleavage as a set of tandemly repeated dodecamers, the DR2 repeats. Endonuclease levels vary according to the proliferative state of the cell; little or no activity is detectable in extracts from quiescent cells, whereas high levels are expressed in dividing cells. Also, infection of density-arrested BSC-1 cells with HSV-1 induces a substantial increase (at least 35-fold) in endonucleolytic activity, which is first detectable at about 1 hr after infection at 32 degrees C. The elevated levels of enzyme activity then persist throughout the viral life cycle. In addition to the HSV-1 DR2 repeats, certain other G+C-rich sequences with an asymmetric distribution of purines and pyrimidines on the DNA strands and with appropriate sequences and lengths are substrates for the nuclease. These data indicate that target site recognition by the enzyme is conformation specific rather than sequence specific.

Animals↗
PubMed1991

[Victoria blue: staining properties in orthology and pathology].

The staining properties of the cationic dye Victoria Blue are summarized in consideration of the findings in the literature and own findings. Dependent on the staining conditions (with or without preoxidation of tissue sections), different structures and substances are stained by Victoria Blue. Without preoxidation elastic fibres, acid glycosaminoglycanes and DNA predominantly stained, but with preoxidation the dye stained insulin, some peptide hormones and secretion products, HBs-antigen, and lipofuscin. The chemism of the histochemical reaction is not quite understood yet.

Animals↗
PubMed1990

Morphological findings in the liver of diabetic rats after intraportal transplantation of neonatal isologous pancreatic islets.

Morphological (light microscopical, immunohistological and electron microscopical) findings in the recipient liver of rats with streptozotocin-induced diabetes, obtained 9 months after intraportal injection of neonatal isologous pancreatic islets, are described and their significance discussed. The results support the assumption of active ingrowth of nonmyelinated nerve fibers into the islet isografts. The hepatocytes surrounding the islet isografts contain--obviously owing to the influence of unusually high and locally variable concentrations of insulin--a focally increased number of enlarged mitochondria, abundant glycogen and a smaller amount of neutral fat droplets. Furthermore, hepatocytes and cells looking like hepatocytes (hepatocyte-like cells) with typically structured cytoplasmic beta (insulin) granules were found bordering the islet isografts. These results could be interpreted as an expression of artificial or nonartificial fusion of beta cells with hepatocytes, i.e. formation of hybrid cells ("in vivo hybridization"). Alternatively, they might reflect insulin uptake and storage in the hepatocytes. In addition, these findings suggest that contact between neonatal islet tissue and liver tissue could be a trigger for the in vivo transformation (modulation) of differentiated cells of similar embryonic development in the adult organism.

Animals↗
PubMed1990

[Gomori reactions in orthology and pathology].

The following four basic histochemical reactions were developed by Gomori (1904-1957): 1. Silver impregnation of reticular fibres (1937); 2. Metal salt principle for detection of hydrolytic enzyme activity (1939); 3. Silver-methenamine reaction (1946); 4. Aldehyde fuchsin reaction (1950). These reactions and their modifications have assumed growing importance to expansion of knowledge, primarily on orthological and pathobiological problems.

Histocytochemistry↗
PubMed1990

[Proliferation of beta cells after syngeneic transplantation of isolated Langerhans cells into the spleens of diabetic rats].

Syngeneic transplantation of cultured and functionally characterized neonatal islet into the spleen of streptozotocin diabetic Lewis rats resulted in long time survival up to 200 days and in plasma glucose levels lower than 9 mmol/l. The daily plasma glucose profile of transplanted rats had shown significantly above that of non diabetic control rats. 200 days after transplantation morphologically intact, insulin containing beta-cells were demonstrable in the spleen, thus demonstrating the long-term survival of functioning islet cells. Proliferation of beta-cells was shown in the transplanted islets. In addition, beta-cell clusters were found which derived from pancreatic ductules transplanted together with the isolated islets into the spleen. Mitose were visible within ductular epithelial cells. The proliferative response of islets after intrasplenic transplantation is probably the result of a long-term stimulation by slightly enhanced plasma glucose values of the transplanted acceptors compared to control animals.

Animals↗
PubMed1979

Thymidylate synthetase from Escherichia coli K12. Purification, and dependence of kinetic properties on sugar conformation and size of the 2' substituent.

Thymidylate synthetase from Escherichia coli K12 has been purified 3600-fold by a series of chromatographic procedures. The final preparation had a specific activity of 1.47 units/mg protein and was approximately 80% pure. The enzyme is a dimer of relative molecular mass, Mr, 64000 composed of two subunits of Mr 32,000 each. Its isoelectric point is 4.7 and it is stimulated by Mg2+. Michaelis constants for (+)5,10-methylene-5,6,7,8-tetrahydrofolate [(+)CH2H4folate] were 0.014 mM in the case of methylation of 2'-deoxyuridine-5'-phosphate (dUMP) and 0.55 mM when it served as methyl-group donor for 2'-fluoro-2'-deoxyuridine-5'-phosphate (dUflMP); the corresponding Km values for dUMP and dUflMP were 0.01 mM and 0.11 mM, respectively. The activation energies for the two reactions were found to be 72.8 kJ/mol (methylation of dUMP) and 66.1 kJ/mol (methylation of dUflMP). The data support a recognition mechanism between thymidylate synthetase and that fraction of the nucleotide the sugar moiety of which is in the 2'-endo-3'-exo conformation.

Carbohydrate Conformation↗
PubMed1979

[On the localization of sorbitol dehydrogenase in the rat kidney (author's transl)].

We have investigated the localization and demonstration of sorbitol dehydrogenase activity in the rat kidney by comparative histochemical-electrophoretical technique. Under histochemical conditions an adequate demonstration of the activity of the sorbitol dehydrogenase in native sections is possible by membrane incubating technique in presence of PMS and KCN. In the glomerulum the strong and uniform reaction with regard to the specifity is not clear. In the glomerula of semithin sections from glutaraldehyde fixed, incubated and Epon-embedded cryostate sections the reaction product is localized predominantly in the maesangium cells. By micropolyacrylamidgel gradient electrophoresis of the supernatant from the kidney cortex and of isolated glomerula 2 sorbitol dehydrogenase fractions were found. The results are discussed in connection with the specifity of the reaction.

Animals↗
PubMed1978

2'-Deoxy-2'-fluorouridine-5'-phosphate: an alternative substrate for thymidylate synthetase from Escherichia coli K12.

The substrate specificity of 2'-deoxy-2'-substituted uridines and their 5'-phosphates towards thymidylate synthetase from Escherichia coli K12 was investigated. Besides the natural substrate 2'-deoxyuridine-5'-phosphate (dUMP), only 2'-deoxy-2'-fluorouridine-5'-phosphate (dUflMP) was a substrate. The KM of dUflMP is 11 times higher than that of dUMP, while the Vmax values are virtually the same. It is concluded that the size of the 2'-substituent and not its polarity (and the concomitant conformational change) determines substrate specificity of thymidylate synthetase.

Deoxyuracil Nucleotides↗
PubMed1978

On the histochemistry of prostaglandin-dehydrogenase.

Using PGF2alpha as substrate the PGDH-activity was localised in the male and in the female rat kidney by histochemical technique. The reaction is independent of the presence of NAD, but with NAD the reaction intensity is enhanced. The effectors phenazine methosulphate, Triton X 100 and Tween 80 showed no enhancing effect on the enzyme activity. In the rat kidney we have found the reaction product predominantly in the inner cortex (straight portion of the proximal tubules), however, sex dependent differences of PGDH-activity and localization are visible.

15-Oxoprostaglandin 13-Reductase↗
PubMed1978

[On the histochemistry of xanthine dehydrogenase (author's transl)].

We have investigated the enzymes of the XDH-XOD-system by histochemical technique based on a model study for histochemical tetrazolium reduction by flavine enzymes. We have not found a reaction in native sections from liver, kidney and duodenum of adult male Wistar rats. The effectors PMS, Triton X-100 and Tween 80 were inefficient. A strong reaction was observed after a short fixation (10 min) of the sections with glutaraldehyde predominantly in the duodenal epithel cells. The intensity of the reaction was much stronger in sections of liver, kidney and duodenum by influence of the effector PMS and the detergents Triton X-100 and Tween 80. The application of the membrane technique does not show advantages in the histochemical demonstration of the XDH-XOD-system. The specificity of the reaction is discussed under the aspect of the complexity of the XDH-XOD-system shown by biochemical investigations.

Animals↗
PubMed1977

The problem of diabetic angiolopathy in sand rats (Psammomys obesus).

No diabetic angiolopathy was found in the retinas, kidneys and skeletal muscles of protodiabetic and overtly diabetic sand rats. The terminal blood vessels were investigated using histological, enzyme histochemical, immunofluorescence microscopic, autoradiographic and electron microscopic methods. There seems to be little or no connection in sand rats between the diabetic metabolism syndrome and the metabolic process leading to angiolopathy.

Animals↗