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1.
Rolf Altenburger Sibylle Abarzua Rainer Callies L. Horst Grimme Adalbert Mayer Dieter Leibfritz 《Archives of microbiology》1991,156(6):471-476
Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo 31P NMR. Furthermore, the energy status of the cells remains regulated. In vivo 15N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show -aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.Abbreviations GABA
-aminobutyric acid
- GOGAT
glutamate synthase
- GS
glutamine synthetase
- MDP
methylene diphosphonate
- MOPSO
3-(N-morpholino)-2-hydroxy-propanesulfonic acid
- NDPS
nucieoside diphosphosugars
- NOE
nuclear Overhauser effect
- NMR
nuclear magnetic resonance
For convenience, the term ammonia is used throughout to denote ammonia or ammonium ion when there is no good evidence as to which chemical species is involved 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
6.
S. Abarzua R. Altenburger R. Callies L.-H. Grimme A. Mayer D. Leibfritz U. Schiewer 《Physiologia plantarum》1993,89(3):659-663
Over a period of several days, rhythmic changes in extracellular NH+ 4 concentration take place in cultures of the cyanobacterium Microcystis firma (Bré et Lenorm.) Schmidle, strain Gromov/St. Petersb. 398, under conditions of restricted CO2 supply and light/dark alternation. The changes are enhanced by nitrate supply. Among the various processes generating intracellular NH+ 4 (NH4 4 uptake, NO− 3 reduction, protein and amino acid degradation, photorespiration), NO− 3 reduction appears as the one most important. This can be concluded from experiments with and without nitrate and/or ammonium in the medium. In the presence of saturating CO2 , continuous light, or continuous darkness, rhythmic NH+4 4 oscillations are not induced. Studies of the incorporation of NH+ 4 nitrogen by in vivo 15 N-NMR show that if CO2 is supplied, 15 N is accumulated in several components with the following time course: in the first hour in Gln (δ), in the second hour in the α-amino groups of most nonbranched amino acids, in the third hour in γ-aminobutyric acid (GABA), Orn (δ) and Lys (ε), and in the sixth hour in Ala. Carbon limitation, however, results in accumulation of label in the amide nitrogen of glutamine only. 相似文献
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The nucleotide sequence of uncloned mouse satellite DNA has been determined by analyzing Sau96I restriction fragments that correspond to the repeat unit of the satellite DNA. An unambiguous sequence of 234 bp has been obtained. The sequence of the first 250 bases from dimeric satellite fragments present in Sau96I limit digests corresponds almost exactly to two tandemly arranged monomer sequences including a complete Sau96I site in the center. This is in agreement with the hypothesis that a low level of divergence which cannot be detected in sequence analyses of uncloned DNA is responsible for the appearance of dimeric fragments. Most of the sequence of the 5% fraction of Sau96 monomers that are susceptible to TaqI has also been determined and has been found to agree completely with the prototype sequence. The monomer sequence is internally repetitious being composed of eight diverged subrepeats. The divergence pattern has interesting implications for theories on the evolution of mouse satellite DNA. 相似文献
9.
Micrococcal nuclease is shown to cleave DNA under conditions of partial digestion in a specific manner. Sequences of the type 5'CATA and 5'CTA are attacked preferentially, followed by exonucleolytic degradation at the newly generated DNA termini. GC-rich flanking sequences further increase the probability of initial attack. Unexpectedly, long stretches containing only A and T are spared by the nuclease. These results, which were obtained with spared by the nuclease. These results, which were obtained with mouse satellite DNA and two fragments from the plasmid pBR22, do not support the previous contention that it is the regions of high At-content which are initially cleaved by micrococcal nuclease. This specificity of micrococcal nuclease complicates its use in experiments intended to monitor the nucleoprotein structure of a DNA sequence in chromatin. 相似文献
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