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G Schimpff-Weiland

Publications and source records attributed to G Schimpff-Weiland.

6 recordsLinked to original sources
PubMed1987

DNA methylation in wheat. Purification and properties of DNA methyltransferase.

The origin and function of the large amount of 5-methylcytosine in plant DNA is not well understood. As a tool for in vitro studies of methylcytosine formation in plants we have isolated and characterized the DNA methyltransferase present in germinating wheat embryo. An enzyme fraction enriched 300-fold over the tissue homogenate was obtained by salt extraction of nuclei, chromatography on DEAE-cellulose, Sephadex G-75, blue Sepharose and on DNA immobilized on cellulose. It catalyzes the methylation of cytosine residues in double-stranded DNAs isolated from wheat, maize, calf thymus or bacteria using S-adenosylmethionine as methyl donor. The efficient methylation of both an unmethylated plasmid DNA and its hemimethylated derivative indicate that the wheat DNA methylase can function de novo and in maintenance methylation. A relative molecular mass of 50,000-55,000 was estimated by gel permeation chromatography and sucrose density gradient centrifugation. Polyacrylamide gel electrophoresis showed the presence of a protein of Mr = 50,000 and one other component (Mr = 35,000). The preference for endogenous, double-stranded DNA as substrate and the lower molecular mass distinguish wheat DNA methyltransferase from the DNA methylases obtained from mammalian sources. The properties of the wheat enzyme resemble, however, those of the DNA methylase isolated from the alga Chlamydomonas reinhardii, suggesting that plant cells possess their own type of DNA methyltransferase for the biosynthesis of their high methylcytosine content in DNA.

Amino Acid Sequence↗
PubMed1985

Unexpected specificity in the thioredoxin activation of fructose-bis-phosphatases from different plants.

Green seedlings of soy bean and wheat contain, like the plant seeds, multiple thioredoxin proteins which possess all typical thioredoxin properties but are inactive in the stimulation assay with spinach fructose-bis-phosphatase. However the pure proteins do have thioredoxin f activity when tested with homologous enzymes isolated from soy bean or wheat leaves, respectively, in the presence of Mg++. This new type of species specificity, unknown in all other in vitro assays of reduced thioredoxins, has to be considered in characterizing complete thioredoxin profiles in plants.

Bacterial Proteins↗
PubMed1980

Deoxyribonucleotide biosynthesis in synchronous algae cells.

Synchronous cells of the green alga, Scenedesmus obliquus, cultured in a 14-h/10-h light/dark regime, contain a peak of ribonucleoside-diphosphate reductase activity and maximum deoxyribonucleoside 5'-triphosphate concentrations at the 12th hour of the cell cycle, coinciding with DNA synthesis and preceding the formation of eight daughter cells. The intracellular dTTP pool reaches 4.5 pmol and the other pools 2-3 pmol/10(6) cells. Algal reductase activity is sensitive to cycloheximide, but not to lincomycin. These correlations demonstrate the functioning of the NDP leads to dNDP leads to dNTP pathway of DNA precursor biosynthesis in plant cells. In the presence of 20 micrograms 5-fluorodeoxyuridine/ml, an inhibitor of thymidylate synthesis, the dTTP pool is rapidly depleted and DNA synthesis ceases. 5-Fluorouracil and methotrexate produce similar effects. At the same time the ribonucleotide reductase activity and also the dATP pool are greatly increased, especially when fluorodeoxyuridine treatment is combined with continued illumination of the algae. In contrast, arabinosylcytosine, an inhibitor of DNA replication, has no effect on ribonucleotide reduction. The control of de novo enzyme synthesis in the eucaryotic algae therefore appears to depend on the presence of dTTP (or a related nucleotide), but not directly coupled to DNA synthesis. This interdependence resembles the situation observed in HeLa cells, while it may differ in detail from control mechanisms of ribonucleotide reductase studied in bacteria.

Cell Cycle↗
PubMedDate not supplied

Aurintricarboxylic acid and polynucleotides as novel inhibitors of ribonucleotide reductases.

Ribonucleoside diphosphate reductases isolated from Escherichia coli, baker's yeast, Ehrlich ascites tumor cells, and unicellular green alga (Scenedesmus obliquus) are inhibited strongly and uniformly by the polymeric triphenylmethane dye, aurintricarboxylic acid. The molecule appears to interact simultaneously with the enzyme's various nucleotide and catalytic (iron-organic radical) sites. Oligo- and polyribonucleotides are also inhibitory. These reactions serve as models of the probably physiologic regulation of ribonucleotide reduction exerted by natural inhibitors. Partial characterization of an inhibitor fraction found in wheat seed embryo is described.

Animals↗