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1.
Uri Pick 《Biometals》2004,17(1):79-86
It is demonstrated that Antimycin A (AA), a respiratory inhibitor produced by Streptomyces bacteria, forms lipophylic complexes with Fe(III) ions. Spectroscopic titration indicates that Fe(III) ions interact with 2AA molecules. At growth-limiting Fe concentrations, AA mediates Fe uptake and promotes growth and chlorophyll synthesis better than other Fe chelators in the halotolerant alga Dunaliella salina. It is proposed that AA enhances Fe bioavailability in hypersaline solutions by formation of lipophylic Fe-AA complexes which are taken-up and utilized by the algae. The results suggest that the respiratory inhibitor AA can affect Fe metabolism in microorganisms. 相似文献
2.
Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase-deficient mutant) plants exposed to NH4 NO3 总被引:1,自引:0,他引:1
David C. Taylor Barry J. Shelp Louise M. Nelson Bernard Grodzinski 《Physiologia plantarum》1988,74(4):593-601
Carbon and nitrogen partitioning was examined in a wild-type and a nitrate reductase-deficient mutant (A317) of Pisum sativum L. (ev. Juneau), effectively inoculated with two strains of Rhizobium leguminosarum (128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH4 NO3 . In wild-type symbioses the application of NH4 NO3 significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [14 C]-labelled (NO3 − , NH4 + , amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO3 − and NH4 + or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host and Rhizobium strain must be studied before generalizations about Rhizobium /legume interactions are made. 相似文献
3.
Rhizoglyphus robini Claparède (Acari: Astigmata: Acaridae) is proposed as a model laboratory animal for biological, ecological, physiological and toxicological studies. The mite is easy and inexpensive to rear, quite fecund, convenient to manipulate, and may rapidly be raised to gram quantities. Examples are presented of its use in soil pest ecology and control studies, and in physiological, biochemical and toxicological investigations. Efforts to explore the induction of detoxification systems by various chemicals, and a demonstration of its control by solarization, are also described. 相似文献
4.
Summary A procedure to reconstitute CF0CF1 proteoliposomes by gel filtration through a Sephadex-column pre-equilibrated with valinomycin and potassium is described. Proteoliposomes reconstituted by this procedure catalyze an ATP-induced pH of 2.5 to 3.5 units. pH was measured with either 9-aminoacridine or with the pH indicator pyranine trapped inside the proteoliposomes. CF0CF1 proteoliposomes prepared by conventional techniques catalyzed an ATP-induced formation, but were unable to catalyze an ATP-induced pH even in the presence of valinomycin.The ATP-induced pH was sensitive to uncouplers and energy transfer inhibitors and was increased at low temperatures. It is suggested that ATP-induced pH was observed in these proteoliposomes due to the efficient removal of intravesicular ammonium introduced with the CF0CF1 preparation. The ammonium acted as an internal buffer, and thus prevented an observable pH formation. 相似文献
5.
6.
Salt-induced cooperativity in ATPase activity of plasma membrane-enriched fractions from cultured Citrus cells: kinetic evidence 总被引:1,自引:0,他引:1
ATPase activity was studied in plasma membrane-enriched fractions prepared from cultured Citrus sinensis L. cv. Osbeck cells. In general, properties of the plasma membrane ATPase from cultured cells, such as optimal pH and temperature. Vmax and Km were similar to those already observed in higher plants. The effects of high salt concentrations on ATPase activity were studied in membrane fractions derived from salt-sensitive and salt-tolerant cells grown in the presence or absence of salt. NaCl did not have an in vivo effect on Vmax and the apparent Km value for ATP. However, high concentrations of NaCl, or KCl, added in vitro, induced cooperativity in the enzyme and reduced the affinity of the enzyme for its substrate. Isoosmolar concentrations of sucrose or choline chloride failed to do so. Our results suggest that the plasma membrane ATPase of Citrus cells has more than one substrate-binding site on the native form of the enzyme which interact in the presence of salt and act independently in its absence. 相似文献
7.
Uri S. Ladror Gary T. Wang William L. Klein Thomas F. Holzman Grant A. Krafft 《Journal of Protein Chemistry》1994,13(4):357-366
Fluorogenic peptide substrates designed to encompass the reported-secretory and amyloidogenic cleavage sites of the amyloid- precursor protein (PP) were used to analyze proteinase activities in brain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate atpH 7.5 in control and AD brains produced a major endopeptidase cleavage at the Lys687-Leu688 bond (PP770 numbering), consistent with thePP secretase cleavage. Activity in control brains against the amyloidogenic substrate atpH 7.5 produced one cleavage at the Ala673-Glu674 bond, two residues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one residue from the amyloidogenic site. Both endopeptidase and carboxypeptidase activities in AD brains were lower than in control brains. Proteinase activities against the secretory substrate had a major optimum atpH 3.0–4.0 and another atpH 6.0–7.5. Proteinase activities against the amyloidogenic substrate had a major optimum at or belowpH 3.0 and another atpH 6.0. Using both substrates, activities at lowpH were higher in AD brains than in controls, while atpH above 6.5, activities in control brains were higher than in AD. These results indicate that the levels of proteolytic enzymes in AD brains are altered relative to controls.Abbreviations A
Amyloid-
- ACN
acetonitrile
- AD
Alzheimer's disease
- PP
amyloid- precursor protein
- DABCYL
4-(4-dimethylaminophenylazo)-benzoic acid
- EDANS
5-{(2-aminoethyl)amino}napthalene-1-sulfonic acid
- MES
morpholinoethane sulfonic acid
- MOPS
morpholino-propane sulfonic acid
- RP-HPLC
reverse-phase high-performance liquid chromatography
- SDS-PAGE
sodium do-decyl sulfate-polyacrylamide gel electrophoresis
- TFA
tri-fluoroacetic acid
- Tris
tris(hydroxyethyl)aminomethane 相似文献
8.
The involvement of a vanadate-sensitive ATPase in plasma membranes of a salt tolerant cyanobacterium
Rachel Gabbay-Azaria Uri Pick Gozal Ben-Hayyim Elisha Tel-Or 《Physiologia plantarum》1994,90(4):692-698
Plasma membranes of the marine cyanobacterium Spirulina subsalsa were tested for ATPase activity, and for involvement in salt stress. Transition of cells from saline to hypersaline medium enhances the respiratory activity associated with extrusion of Na+ and Cl− , and persisting salt stress induces synthesis of respiratory enzymes in the plasma membranes. The membranes possess an ATPase, specific for ATP and Mg2+ and sensitive to orthovanadate and dicyclohexylcarbodiimide. Immunoblot analysis of plasma membrane polypeptides from Spirulina subsalsa with anti- Arabidopsis H+ -ATPase serum identified a single polypeptide of 100 kDa, which cross-reacted with the antibodies. An unusual feature of this ATPase is a specific stimulation by Na+ ions. Prolonged adaptation of S. subsals cells to hypersaline conditions induced an increase in ATPase activity in subsequent plasma membrane preparations, as well as a higher content of the 100 kDa polypeptide. It is suggested that the ATPase investigated is an H+ -pump, which is involved in extrusion of Na+ and in conferring resistance to salt stress. 相似文献
9.
The toad, Bufo viridis , can live for several months without access to free water, absorbing soil-bound water down a water-potential gradient created, mainly, by accumulating urea in its body fluids. We investigated if the retention of urine was sufficient to account for the rate of accumulation or if an increased rate of urea production was needed in order to do so. The basal rate of urea production in unfed animals in the absence of osmotic stress was estimated by two methods; first, analysis of the bathing medium and, secondly, collection and analysis of urine at two-hourly intervals. This was then repeated with animals fed a weight-maintaining diet. Generally similar results were obtained by either method in both fed and unfed animals, although higher urea production rates were found in the former. Although it had been planned to apply the short interval method to toads with free access to water, the control condition for toads transferred to soil, it proved to be impracticable. Some animals did not bathe for almost a day, during which time minute quantities of urine were obtained. Larger volumes were only produced during or after bathing. Consequently, animals which were partially immersed in water were substituted as controls. Total urea content was determined in these and in toads after a week on soil. The calculated increase was compared to that which could be expected from urine retention. It was found that urea accumulated at more than twice the predicted rate. When rates of accumulation were calculated over longer periods, urine retention alone was sufficient to account for them within three weeks on soil, the usual period required for acclimation. We concluded that B. viridis increased its rate of urea production only for a short period, until a favourable water potential gradient was achieved. 相似文献
10.
The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil. 相似文献