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81.
82.
Utilization of limiting concentrations of ortho-phosphate and production of extracellular organic phosphates in cultures of marine diatoms 总被引:1,自引:0,他引:1
The utilization of ortho-phosphate by two coastal marine diatomspecies, Nitzschia closterium and Cyclotella cryptica, was studiedin batch cultures. The hypothesis was tested that thresholdconcentrations in the phosphate uptake determine the lower limitof environmental phosphate, permitting the existence of species.The turn-over time of residual medium phosphate in culturesis {small tilde}10 min, indicating a rapid equilibration ofconcentration dependent on uptake with leakage of ortho-phosphate.Increasing phosphate starvation in cultures diminished the residualortho-phosphate in the range of {small tilde}60<2nmol l1, as measured radiochemically after elution onSephadex® G-10 gel. These concentrations encompass the rangeof limiting phosphate concentration in continuous cultures ofthe few microalgae, for which these concentrations are actuallymeasured. The diatoms excreted {small tilde}20100 nmolI1 of organic phosphate. One dominating compound, probablyan unusual nucleotide, was incompletely or not resorbed underphosphate starvation. In contrast, Nitzschia closterium excretedunder ample phosphate supply a series of three related compounds,probably phospholipids, that were resorbed under depletion.The association of the organic phosphates with macromolecularexudates is interpreted, along with the other observations,as an indication for a hardly explored periplasmatic phosphatemetabolism in these algae.
3Dedicated to Prof. Dr. H.-A. von Stosch in honour of his 75thbirthday.
4This study was conducted at the University of Marburg undersupport of the Humboldt Foundation Publication no. 64 of theproject "Biological Research of the Eems-Dollard Estuary". 相似文献
83.
84.
Differing Neurochemical and Morphological Sequelae of Global Ischemia: Comparison of Single- and Multiple-Insult Paradigms 总被引:3,自引:0,他引:3
Baowan Lin Mordecai Y.-T. Globus W. Dalton Dietrich Raul Busto Elena Martinez Myron D. Ginsberg 《Journal of neurochemistry》1992,59(6):2213-2223
The purpose of this investigation was to investigate pathomechanisms responsible for the deleterious effects of repeated episodes of brief forebrain ischemia. Halothane-anesthetized male Wistar rats were subjected to either (a) a single 15-min period or (b) three 5-min periods (separated by 1 h) of global forebrain ischemia by bilateral carotid artery occlusions plus hypotension (50 mm Hg), followed by various periods of recirculation. Brain temperature was normothermic throughout. In one series of rats, extracellular levels of glutamate, glycine, and gamma-aminobutyric acid (GABA) were measured in the dorsolateral striatum (n = 6-8 per group) and lateral thalamus (n = 4-6 per group) by microdialysis and HPLC before and during ischemia and during 3-5 h of recirculation. In a parallel series of rats (n = 6 per group), ischemic cell change was quantified at 2 (dark neurons), 24, or 72 h following either single or multiple ischemic insults. A single 15-min ischemic period led to massive glutamate release (13-fold increase; p = 0.001), which returned to normal by 20-30 min of recirculation and remained normal thereafter. By contrast, in rats with three 5-min periods of ischemia, the glutamate level rise with each repeated insult (four- to 4.5-fold; p < or = 0.02) was smaller than that observed during the single 15-min insult, but a late sustained rise (five- to six-fold; p < 0.05) occurred at 2-3 h of recirculation. Brief ischemia-induced elevations of glycine and GABA levels were detected in both the single- and multiple-insult groups, with normalization during recirculation. In contrast, the excitotoxic index, a composite measure of neurotransmitter release ([glutamate] x [glycine]/[GABA]), differed markedly following single versus multiple insults (p = 0.002 by repeated-measures analysis of variance) and increased by seven- to 12-fold (p < 0.05) at 1-3 h following the third insult. The total amount of glutamate released was 3.3-fold higher in the multiple-insult than in the single-insult group (p < 0.02). At 2 h of recirculation, histopathological analysis of dorsolateral striatum showed a significantly greater frequency of dark neurons in the multiple- than in the single-insult group (p < 0.05 by analysis of variance). In the thalamus, a higher frequency of ischemic neurons was seen in the multiple-than in the single-insult group at all intervals studied. Thus, in rats with multiple ischemic insults, accelerated ischemic damage was found in the striatum, and severe ischemic injury was documented in the thalamus.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
85.
Stefan Schünemann Dietrich Schulte-Frohlinde 《Molecular & general genetics : MGG》1992,233(3):348-354
Summary The survival of M13 DNA was studied after partial replacement of thymine by uracil in the bacteriophage. Uracils carry the same genetic information as the thymines. Nevertheless in Escherichia coli wild-type cells, uracils in DNA are replaced by thymines by excision repair initiated by uracil-DNA glycosylase (UDG). Thus inactivation of uracil-containing phage DNA is solely due to repair initiated by UDG. Incorporation of uracils was achieved in one or in both strands, either randomly or site-specifically using differently uracylated oligonucleotides. The results show that up to 580 uracils can be repaired without a significant decrease in survival if the uracils are localized in the (–) strand only. Incorporation of 246 uracils into the (+) strand leads to 30% or 10% survival when expressed in Escherichia coli strains CMK and JM103, respectively. However, when uracils are distributed over both strands a sharp decrease in survival occurs. This shows that the repair of two uracils localized in close proximity on opposite strands of the DNA by the excision repair mechanism is difficult, whereas uracils occurring in one strand are repaired more efficiently, irrespective of their number. 相似文献
86.
R. B. Dietrich 《The Western journal of medicine》1992,156(3):296-297
87.
J B Dietrich 《Cellular and molecular biology, including cyto-enzymology》1992,38(2):95-114
Tyrosine aminotransferase (L-tyrosine: 2 oxoglutarate aminotransferase; EC 2.6.1.5; TATase) is the first enzyme in the catabolic pathway of tyrosine. The gene of this transaminase is regulated by glucocorticoid hormones as well as via the cAMP pathway. This review gives a brief survey of the structural and physico-chemical properties of this well-known protein. A comparative study of the properties of TATase with other aminotransferases is also included to analyse this molecule for itself, and not only as a marker used in studies on enzymatic induction. Finally, the regulation of the gene expression is presented, in order to underline a few important features of this model. 相似文献
88.
Chemotaxis and nod Gene Activity of Bradyrhizobium japonicum in Response to Hydroxycinnamic Acids and Isoflavonoids 总被引:9,自引:4,他引:5 下载免费PDF全文
For Bradyrhizobium japonicum, the chemotactic and the nod gene-inducing effects of hydroxycinnamic acids and two of their derivatives were compared with those of isoflavonoids. Only the hydroxycinnamic acids were strong chemoattractants, while the other substances tested were chemotactically inactive. Besides the known nod gene induction by isoflavonoids, a weak nod gene induction by coniferyl alcohol, chlorogenic acid, and ferulic acid was found. 相似文献
89.
R Nilius K Stuhec R Dietrich 《Physiological research / Academia Scientiarum Bohemoslovaca》1991,40(1):95-102
Lymphocytic dipeptidylpeptidase IV (DPP-IV, E.C. 3.4.14.5) is described as a marker enzyme of immunostimulant T-lymphocytes as well as functional characteristic of interleukin-2-producing cells. Cytochemical staining of DPP-IV positive lymphocytes and measurements of DPP-IV activity in mononuclear cells and in sera of patients suffering from different kinds of liver diseases were performed to evaluate the average activities in positive cells. The results demonstrated that this serine exopeptidase exhibits extremely low activity in autoimmune chronic hepatopathies. On the contrary, hepatitis-B-associated liver diseases were connected with markedly increased values. Furthermore, significant differences of DPP-IV activity were found in different kinds of acute and chronic liver diseases. These findings are discussed in connection with the participation of dipeptidylpeptidase IV in impaired immunoregulation of the altered liver. 相似文献
90.
Summary Experiments with black locust (Robinia pseudoacacia L.) seedlings grown under strictly controlled laboratory conditions indicated that the availability of nitrate has a marked impact on nitrogen fixation. When nitrate concentrations were very low, both nodulation and seedling growth were impaired, whereas nitrate concentrations high enough to promote plant growth strongly inhibited symbiotic nitrogen fixation. When nitrate was added to the growth medium after infection, nodulation and nitrogen fixation of the seedlings decreased. This effect was even more marked when nitrate was applied before infection with rhizobia. Higher nitrogen concentrations also reduced nodule number and nodule mass when applied simultaneously with the infecting bacteria. The contribution of symbiotic nitrogen fixation to black locust shoot mass by far exceeded its effects on shoot length and root mass. When nitrate availability was very low, specific nitrogen fixation (i. e. nitrogenase activity per nodule wet weight) was improved with increasing nitrogen supply, but rapidly decreased with higher nitrogen concentrations. 相似文献