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991.
992.
Tissue-specific iron content is tightly regulated to simultaneously satisfy specialized metabolic needs and avoid cytotoxicity. In the brain, disruption of iron homeostasis may occur in acute as well as progressive injuries associated with neuronal dysfunction and death. We hypothesized that adverse effects of disrupted metal homeostasis on brain function may involve impairment of DNA repair processes. Because in the brain, the base excision repair (BER) pathway is central for handling oxidatively damaged DNA, we investigated effects of elevated iron and zinc on key BER enzymes. In vitro DNA repair assays revealed inhibitory effects of metals on BER activities, including the incision of abasic sites, 5'-flap cleavage, gap filling DNA synthesis and ligation. Using the comet assay, we showed that while metals at concentrations which inhibit BER activities in in vitro assays, did not induce direct genomic damage in cultured primary neurons, they significantly delayed repair of genomic DNA damage induced by sublethal exposure to H2 O2 . Thus, in the brain even a mild transient metal overload, may adversely affect the DNA repair capacity and thereby compromise genomic integrity and initiate long-term deleterious sequelae including neuronal dysfunction and death. 相似文献
993.
A factorial culture experiment was designed to investigate the influence of light regimes and of some metal chelators on the accumulation of cadmium by Lemna gibba L. The plants were grown in a complete nutrient solution containing Cd2+ concentrations ranging from 0 to 27 μ M with or without EDTA, ethylenediamine-N,N'- bis -( o -hydroxyphenylacetic acid) (EDDHA) or salicylic acid. Each experiment was run for eight days in 18 h:6 h light:dark or continuous light. An increase in the Cd2+ concentration in plants and a simultaneous drop in accumulation efficiency (ratio of Cd2+ concentration in plants to the initial Cd2+ concentration in the nutrient solution) with increasing ambient Cd2+ levels was best represented by regression power curves. At the lowest Cd2+ concentration which caused a significant decrease in the relative growth rate of duckweed, there was a decrease in manganese and zinc and an increase in the iron level in the plants. EDDHA and EDTA protected in some cases against the toxic action of cadmium without preventing its uptake by plants. It was thus observed that 9 μ M or higher levels of Cd2+ were toxic to Lemna gibba depending on the chelator and light regime. Duckweed grown in continuous light produced, in general, more dry matter and hence accumulated more cadmium. 相似文献
994.
B.J. Parsons G.O. Phillips B. Thomas D.J. Wedlock A.J. Clarke-Sturman 《International journal of biological macromolecules》1985,7(3):187-192
It is demonstrated using gamma-radiolytic and photolytic techniques that, when O2?- is produced in the presence of catalytic amounts of iron(II) and iron(III) complexes depolymerization of xanthan in aqueous solution occurs. The use of these techniques also allows a quantitative measurement of the efficiency of conversion of O2?- to ?OH in these systems to be made, with the assumption that ?OH is the most likely depolymerizing species present. Using pulse radiolysis and oxidative-reductive depolymerization, the effects of some common anions on the degradation process have been correlated with the reactivities of their related free radicals with xanthan. The effects of other parameters such as ionic strength and temperature on xanthan depolymerization are also detailed 相似文献
995.
Enhancement of In Vivo Tyrosine Hydroxylation in the Rat Adrenal Gland Under Hypoxic Conditions 总被引:2,自引:2,他引:0
Yasunori Hayashi Soichi Miwa Ken Lee Kunio Koshimura Keigo Hamahata Hiroshi Hasegawa Motohatsu Fujiwara Yasuyoshi Watanabe 《Journal of neurochemistry》1990,54(4):1115-1121
We examined the effects of hypoxia (8% O2) on in vivo tyrosine hydroxylation, a rate-limiting step for catecholamine synthesis, in the rat adrenal gland. The hydroxylation rate was determined by measuring the rate of accumulation of 3,4-dihydroxyphenylalanine (DOPA) after decarboxylase inhibition. One hour after hypoxic exposure, DOPA accumulation decreased to 60% of control values, but within 2 h it doubled. At 2 h, the apparent Km values for tyrosine and for biopterin cofactor of tyrosine hydroxylase (TH) in the soluble fraction were unchanged, whereas the Vmax value increased by 30%. The content of total or reduced biopterin was unchanged, but the content of tyrosine increased by 80%. Tyrosine administration had little effect on DOPA accumulation under room air conditions but enhanced DOPA accumulation under hypoxia. After denervation of the adrenal gland, the hypoxia-induced increase in DOPA accumulation and in the Vmax value was abolished, whereas the hypoxia-induced increase in tyrosine content was persistent. These results suggest that in vivo tyrosine hydroxylation is enhanced under hypoxia, although availability of oxygen is reduced. The enhancement is the result of both an increase in tyrosine content coupled with increased sensitivity of TH to changes in tyrosine tissue content and of an increase in dependence of TH on tyrosine levels. The increase in the sensitivity of TH and in the Vmax value is neurally induced, whereas the increase in tyrosine content is regulated by a different mechanism. 相似文献
996.
Summary Transport of iron(III) hydroxamates across the inner membrane into the cytoplasm of Escherichia coli cells is mediated by the FhuC, FhuD and FhuB proteins. We studied the extremely hydrophobic FhuB protein (70 kDa) which is located in the cytoplasmic membrane. The N- and C-terminal halves of the protein [FhuB(N) and FhuB(C)] show homology to each other and to the equivalent polypeptides involved in uptake of ferric dicitrate and of vitamin B2. Various plasmids carrying only one-half of the fhuB gene were expressed in fhuB
– mutants. Only combinations of FhuB(N) and FhuB(C) polypeptides restored sensitivity to albomycin and growth on iron hydroxamates as sole iron source; no activity was obtained with either half of FhuB alone. These results indicate that both halves of FhuB are essential for substrate translocation and that they combine to form an active permease when expressed separately. In addition, a FhuB derivative with a large internal duplication of 271 amino acids was found to be partially active in transport, indicating that the extra portion did not perurb proper insertion of the active FhuB segments into the cytoplasmic membrane. 相似文献
997.
Incubation experiments were carried out to evaluate the feasibility of extracting phosphorus from soil by embedding iron oxide-impregnanted filter paper strips (Pi strips) in soils having a wide range in pH, texture, and extractable-P contents. Under flooded conditions, the amount of P extracted by the Pi strips increased with the period of submergence and embedding time of the Pi strips. Under unsaturated conditions, the Pi strips were found to extract P from soils over a wide range in moisture conditions; however, keeping the soil at moisture level between saturation and field capacity was found to result in maximal sorption of P by the strips. An embedding time of 16 h was found to be adequate.Phosphorus extracted by embedding Pi strips in soil columns for 16 h at field capacity moisture level correlated significantly with P extracted by shaking the soil with 0.01 M CaCl2 solution and a Pi strip for 16 h in the laboratory (r=0.94**). The P extracted by embedding Pi strips correlated best with Bray 1 P in acid soils (r=0.97**) and with Olsen P in alkaline and calcareous soils (r=0.96**). The results of the studies demonstrate the feasibility of developing a nondestructive method of monitoring changes in plant-available P in situ under field conditions. 相似文献
998.
Waterlogging tolerance of four Brassica species, Brassica campestris L., B. carinata A. Br., B. juncea (L.) Czern and Coss., and B. napus L. was assessed after 4 weeks growth in greenhouse at two waterlogging treatments, unflooded control soil, and fully waterlogged soil.Shoot fresh and dry biomass, in both mean and relative terms, was highest in B. juncea and lowest in B. napus at waterlogging treatment. B. carinata was as good as B. juncea in mean shoot fresh and dry matter but it had almost same relative shoot fresh matter as that in B. campestris, but was second highest in relative shoot dry weight.Waterlogging treatment caused a marked reduction in chlorophyll content in all four species but the species difference was not evident. However, B. juncea and B. napus had lower relative total chlorophyll than the other species.A marked increase in soluble protein content of B. juncea and a significant increase in total amino acids in B. carinata was observed under waterlogged conditions as compared to the other species.At the waterlogging regime, an increase in iron content in both shoots and roots was observed in all four species. B. juncea accumulated lower amount of iron in both shoots and roots as compared to the other species, whereas B. carinata had also lower iron in the roots. The species did not differ for shoot manganese content but B. carinata had significantly higher manganese in the roots as compared to the other species. 相似文献
999.
Two phosphate rocks (PR), moderately reactive Hila PR from Colombia and slightly reactive Capinota PR from Bolivia, were compacted
with triple superphosphate (TSP) such that 50% of total P in the mixture was in water-soluble form. The effectiveness of these
materials as phosphorus sources was compared with that of partially acidulated phosphate rocks (PAPR) at 50% acidulation with
sulfuric acid and TSP in Hartsells silt loam (pH 4.5) with maize as the test crop. Huila PAPR and Huila PR compacted with
TSP were as effective as TSP as phosphorus sources. Huila PR was only half as effective. The slightly reactive Capinota PR
with 8.8% Al2O3 + Fe2O3 content was not suited for direct application, and Capinota PAPR was only half as effective as TSP. Capinota PR compacted
with TSP, however, was as effective as TSP. PR compacted with TSP, urea, and KCl was no more effective as phosphorus source
than PR compacted with TSP alone. 相似文献
1000.
P. E. Bacon 《Plant and Soil》1990,121(1):11-19
Experiments were conducted in fields which had a history of nil to four rice (Oryza sativa L.) crops during the previous four summers. Incorporating stubble after each harvest reduced soil nitrate-N content between crops, but increased soil N mineralization potential. During the fourth successive crop, plots where stubble had been incorporated after the previous three harvests had an average 21% more soil NH4N and 22% more N uptake than plots where stubble had been burnt.Soil fertility fell rapidly with increasing numbers of crops, and the unfertilized fifth crop accumulated approximately half the N (60 kg N ha-1) found in the unfertilized first crop (116 kg). Fertilizer N alleviated the effects of annual cropping; the application of 210 kg N ha-1 to the fifth crop (uptake of 156 kg N ha-1) resulted in similar N uptake to the first crop fertilized with 50 kg N ha-1 (154 kg N ha-1).Applying N at sowing had no significant effect on soil NH4-N concentration after permanent flood (PF), while N application at PF resulted in increased NH4-N concentration and N uptake until panicle initiation (PI). N applied at PI increased soil NH4-N concentration at least until the microspore stage.Management factors such as stubble incorporation and increasing N application rate, maintained N supply and enabled successive rice crops to accumulate similar quantities of N at maturity. 相似文献