Biomedical subjects

G Kirchner

Publications and source records attributed to G Kirchner.

7 recordsLinked to original sources

PubMed1992

Migration rates of radionuclides deposited after the Chernobyl accident in various North German soils.

In three soils typical for Northern Germany including Eutric Cambisol, Orthic Podsol and Eutric Histosol (Food and Agriculture Organization nomenclature), distributions of 90Sr, 134Cs, 137Cs and 239Pu + 240Pu in the soil profiles were determined. Sampling was performed more than 3 years after deposition of Chernobyl fallout nuclides. Migration rates calculated with a compartmental model showed no significant differences between Cs originating from either atomic weapons or Chernobyl fallout. This result indicates that Chernobyl Cs may have reached sorption equilibrium with the soil matrix 3 years after the accident. Both the compartmental model and the dispersion equation reproduce distributions of most of the activities, but fail to reproduce some (minor) activity fractions that show increased mobility.

Accidents↗

PubMed1990

Purification and properties of yeast ATP (CTP):tRNA nucleotidyltransferase from wild type and overproducing cells.

ATP (CTP):tRNA nucleotidyltransferase (EC 2.7.7.25) has been purified from wild type cells of the yeast Saccharomyces cerevisiae, as well as from a strain that overproduces the activity. Purification from the wild type strain was accomplished with a multistep protocol including ammonium sulfate fractionation, anion exchange chromatography, gel filtration, and affinity chromatography. The purified enzyme is near homogeneity as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and at 59,000 Da is smaller than reported previously. A similar molecular mass is obtained by gel filtration demonstrating that the enzyme is active as a monomer. The pH optimum for the enzyme is around 9.5. The apparent KM values for ATP and CTP were determined to be 5.6 x 10(-4) M and 1.8 x 10(-4) M, respectively. Purification of the enzyme from the overproducing cells was accomplished by a three step protocol with high yield. The nucleotidyltransferase activity from the overproducing cells had a KM for CTP indistinguishable from that of the wild type enzyme, and the mobility of the protein on sodium dodecyl sulfate gels was the same regardless of the source. Thus, the overproducing strain appears to be a good source for large amounts of yeast nucleotidyltransferase for further biochemical and structural studies.

Chromatography↗

PubMed1990

Isolation of a temperature-sensitive mutant with an altered tRNA nucleotidyltransferase and cloning of the gene encoding tRNA nucleotidyltransferase in the yeast Saccharomyces cerevisiae.

We have isolated a yeast mutant, ts352, that is temperature-sensitive for growth. The mutation has a general effect on mRNA metabolism and a specific effect on tRNA biosynthesis. Cells shifted to the nonpermissive temperature accumulate tRNAs that are shorter than mature tRNAs. The increased ability of these tRNAs to accept ATP demonstrates that growth of the ts352 mutant at the nonpermissive temperature results in accumulation of tRNA with defective 3' ends. The activity of ATP (CTP):tRNA-specific tRNA nucleotidyltransferase can readily be measured in extracts from wild type but not mutant cells. We have cloned and sequenced the wild type allele of the ts352 gene and find significant similarity between the yeast protein sequence predicted from the DNA sequence and the protein predicted from the sequence of the Escherichi coli tRNA nucleotidyltransferase gene. Expression of the yeast gene on a multicopy plasmid increases the activity of the tRNA nucleotidyltransferase in extracts. We conclude that the defect in the ts352 mutant is in the gene coding for yeast tRNA nucleotidyltransferase and that we have isolated the yeast gene that codes for this enzyme.

Amino Acid Sequence↗

PubMed1989

Active bacterial luciferase from a fused gene: expression of a Vibrio harveyi luxAB translational fusion in bacteria, yeast and plant cells.

The luxA and luxB genes encoding the luciferase from Vibrio harvey were fused by site-directed mutagenesis so that one polypeptide was encoded by the fused gene. The fused gene facilitated light production in Escherichia coli, Saccharomyces cerevisiae, and Nicotiana plumbaginifolia when the substrates decanal and reduced flavin mononucleotide were present. The specific activity of the encoded enzyme is not known. In E. coli and S. cerevisiae cells the light emission could be measured in viable, intact cells. The luxAB fusion provides a simple reporter gene for in vivo measurement of promoter strength in these species and may be useful in other systems as well.

Base Sequence↗

PubMed1976

[Fermentation of pyruvate by 7 species of phototrophic purple bacteria].

The dark, anaerobic fermentation of pyruvate under growth conditions was examined with the following species of phototrophic purple bacteria: Rhodospirillum rubrum strains Ha and S1, Rhodopseudomonas gelatinosa strain 2150, Rhodopseudomonas acidophila strain 7050, Rhodopseudomonas palustris strain ATCC 17001, Rhodopseudomonas capsulata strains Kb1 and 6950, Rhodopseudomonas sphaeroides strain ATCC 17023, and Chromatium vinosum strain D. Fermentation balances were established for all experiments. Under fermentative conditions cell protein and dry weight increased only slightly, if at all. The species differed considerably in their fermentative activity; R. rubrum and R. gelatinosa exhibited the highest rates (2-8 mumoles pyruvate/mg protein-h). R. acidophila and R. capsulata showed an intermediate fermentation rate (0.4--2.0 mumoles pyruvate/mg protein-h), while the other strains tested fermented at quite low rates (0.2-0.4 mumoles pyruvate/mg protein-h). The extremes of fermentation times were from 30-380 hours. Based on the products of fermentation which were formed in addition to acetate, formate, and CO2, the species can be grouped as follows: a) R. rubrum, R. gelatinosa, and R. sphaeroides additionally form propionate. b) R. gelatinosa, R. palustris, R. capsulata, R. sphaeroides, and C. vinosum additionally form lactate. R. palustris also produces butyrate. c) R. acidophila and R. capsulata additionally form much 2,3-butanediol, acetoin, and diacetyl. Small amounts of acetoin were formed by the rest of the strains. A comparison of the fermentation of pyruvate by normal and starved cells (4 days in the light without a carbon source) of R. rubrum and R. gelatinosa shows that the latter ferment more slowly and produce less acetate and formate, but more propionate or lactate. The fermentation of pyruvate by R. rubrum was also studied in cultures in which the pH fell (7.2--6.6). Compared with the fermentation at neutral pH (7.3, 7.4), the following differences were found: a slower fermentation rate, an increased production of dry weight, an increased formation of propionate, but a reduced formation of acetate and a very low production of formate.

Acetates↗

PubMedDate not supplied

Zonal turnover of cell poles of Bacillus subtilis.

Turnover of cell walls of Bacillus subtilis occurs in three distinct phases: a lag phase, a relatively rapid phase persisting for 2-3 generations and a much slower phase continuing for several additional generations. A lectin probe revealed that cell pole material was lost during the slow phase of turnover and that the loss of wall occurred in zones, beginning at the cylinder-pole junction and continuing to the cell tip. This is in contrast to cell wall turnover in cylinders where turnover occurs randomly at many surface sites.

Acetylglucosamine↗

PubMedDate not supplied

How does a Bacillus split its septum right down the middle?

This is a speculative paper which considers the possible ways that Gram-positive cells might employ to achieve an even thickness of the two daughter poles resulting from the fission of the cross-wall. The first is that the protonmotive force generated by the extrusion of protons at the cytoplasmic membrane acts to inhibit autolysins to a distance of about 25 nm. The second has to do with the stresses that develop as the poles form. On the tacit assumption that the autolysins will function faster when their substrates are under tension, it is shown how this, too, can lead to even bisection of the cross-wall. These possibilities are not alternative, both probably function.

Bacillus↗