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1.
Specificity and sodium dependence of the active nucleoside transport system in choroid plexus 总被引:5,自引:2,他引:3
The transport of [3H]deoxyuridine by the active nucleoside transport system into the isolated rabbit choroid plexus was measured in vitro under various conditions. Choroid plexuses were incubated in artificial CSF containing 1 microM [3H]deoxyuridine and 1 microM nitrobenzylthioinosine for 5 min under 95% O2-5% CO2 at 37 degrees C and the accumulation of [3H]deoxyuridine measured. Nitrobenzylthioinosine was added to the artificial CSF at a concentration (1 microM) that did not inhibit the active nucleoside transport system but did inhibit the separate, saturable nucleoside efflux system. The active transport of deoxyuridine into the choroid plexus depended on Na+ in the medium, as ouabain, substitution of Li+ and choline for Na+, and poly-L-lysine all inhibited deoxyuridine transport. Thiocyanate in place of chloride and penetrating sulfhydryl reagents also inhibited the active transport of deoxyuridine into choroid plexus. The active transport of deoxyuridine into choroid plexus, which is inhibited by naturally occurring ribo- and deoxyribonucleosides (IC50 = 7-21 microM), was not inhibited (IC50 much greater than 150 microM) by nucleosides with certain alterations on the 2', 3', or 5' positions in D-ribose or 2-deoxy-D-ribose (e.g., adenine arabinoside, 3'-deoxyadenosine, xylosyladenosine); or the pyrimidine or purine rings (e.g., 6-azauridine, xanthosine, 7-methylinosine, or 8-bromoadenosine). Other analogues were effective (IC50 = 8-26 microM; e.g., 5-substituted pyrimidine nucleosides, 7-deazaadenosine, 6-mercaptoguanosine) or less effective (IC50 = 46-145 microM; e.g., 5-azacytidine, 3-deazauridine) inhibitors of deoxyuridine transport into the isolated choroid plexus. 相似文献
2.
Characterization, development, and localization of the deoxycytidine phosphorylating systems in mammalian brain 总被引:2,自引:1,他引:1
The accumulation of deoxycytidine by rabbit and mouse brain was studied in vitro. Brain slices from brain stem, cerebellum, and forebrain of rabbits of various ages (1 day to 2.5 years) and forebrain from adult mice were incubated for various times in artificial CSF containing 6 nM [3H]deoxycytidine at 37 degrees C under 95% O2/5% CO2. Rabbit and mouse brain slices of all ages accumulated [3H]deoxycytidine by a saturable system (IC50 = 4 microM) and converted it to [3H]deoxycytidine phosphates and [3H]DNA. When slices from all brain regions of 1-day-old rabbits were incubated in 6 nM [3H]deoxycytidine for 30 min, tissue-to-medium ratios of 3H were between 1.2 and 2.5 and declined with age, except in cortex; the percentages of total 3H in perchloric acid homogenates of brain slices as [3H]DNA were 10-24% and declined to low levels in middle age. However, at all ages and in all regions tested, 30-85% of the [3H]deoxycytidine within the slices was phosphorylated. After homogenization and subcellular fractionation of the brain slices incubated in [3H]deoxycytidine for 30 min, the highest percentage of [3H]deoxycytidine phosphates plus [3H]DNA was present in the nuclear and mitochondrial fractions of all brain regions. Deoxycytidine phosphates were synthesized from deoxycytidine in all brain regions tested into middle age. 相似文献
3.
Abstract: The mechanisms by which deoxycytidine enters and leaves brain, choroid plexus, and CSF were investigated by injecting [3H]deoxycytidine intraarterially, intravenously, and intraventricularly. After intracarotid injection of deoxycytidine (1.0 μM) into rats, deoxycytidine did not pass through the blood-brain barrier at a faster rate than sucrose. [3H]Deoxycytidine, either alone or together with unlabeled deoxycytidine, was infused at a constant rate into conscious adult rabbits. At 130 min, [3H]deoxycytidine readily entered CSF, choroid plexus, and brain. In brain, approx. 60% of the nonvolatile radioactivity was attributable to [3H]deoxycytidine phosphates. The addition of 0.22 mmol/kg unlabeled deoxycytidine to the infusion syringe decreased the phosphorylation of [3H]deoxycytidine in brain by approx. 50%; the addition of 2.2 mmol/kg of unlabeled deoxycytidine to the infusion syringe decreased the relative entry of [3H]deoxycytidine into CSF and brain by approx. 50 and 75%, respectively. Two hours after the intraventricular injection of [3H]deoxycytidine, [3H]deoxycytidine was rapidly cleared from CSF, in part, to brain, where approx. 65% of the [3H]deoxycytidine was converted to [3H]deoxycytidine phosphates. The intraventricular injection of unlabeled deoxycytidine with the [3H]deoxycytidine decreased the phosphorylation of [3H]deoxycytidine in the brain significantly and also decreased the clearance of [3H]deoxycytidine from the CSF. These results were interpreted as showing that the entry of deoxycytidine from blood into CSF occurs by a saturable transport system within the choroid plexus. Once within the CSF, the deoxycytidine can enter brain, undergo phosphorylation to deoxycytidine phosphates, and subsequently be incorporated into DNA. 相似文献
4.
Emile CL. Marnette Harm Houweling Herman Van Dam Jan Willem Erisman 《Biogeochemistry》1993,23(2):119-144
The chemical composition of surface waters of two Dutch moorland pools and of incident precipitation, was monitored from 1982
to 1990. For this period, sulfur and water budgets were calculated using a hydrochemical model developed for well-mixed non-stratifying
lakes. Total atmospheric deposition of S decreased significantly after 1986 at both locations. A model describing the sulfur
budget in terms of input, output and reduction/oxidation processes predicted a fast decrease of pool water SO4
2− concentrations after a decrease of atmospheric input. However, SO4
2− concentrations in the surface water was lowered only slightly or remained constant. Apparently a source within the lake caused
the unexpectedly high SO4
2− concentrations. The possible supply of SO4
2− from the sediment through regulation by (K-)Al-SO4 containing minerals or desorption of SO4
2− from positively charged surfaces in the sediment was evaluated. Solubility calculations of pore water with respect to alunite,
basaluminite and jurbanite indicated that SO4
2− concentration was not regulated by these minerals. It is suggested here (1) that desorption of SO4
2− from peaty sediments may account for the estimated SO4
2− supply provided that the adsorption complex is periodically recharged by partial oxidation of the upper bottom sediments
and (2) that because of exposure of a part of the pool bottom to the atmosphere during dry summers and subsequent oxidation
of reduced S, the amount of SO4
2− may be provided which complements the decreasing depositional SO4
2− input. In future research these two mechanisms need to be investigated. 相似文献
5.
Sulfate reduction and S-oxidation in a moorland pool sediment 总被引:3,自引:2,他引:1
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4
2– reduction rates in the sediment, (2) depletion of SO4
2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4
2– injection. Rates of SO4
2– consumption in the overlying water were estimated by changes in SO4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4
2– in July 1990 estimated by combination of SO4
2– reduction rates and rates of in situ SO4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4
2– and (2) the presence of mainly non SO4
2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献
6.
MARTIN CLÉMENT CAROLINE CHAMBERLAND JACQUELINE PÉRODIN RICHARD LEDUC GAÉTAN GUILLEMETTE EMANUEL ESCHER 《Journal of receptor and signal transduction research》2013,33(5-6):417-433
Several models of activation mechanisms were proposed for G protein-coupled receptors (GPCRs), yet no direct methods exist for their elucidation. The availability of constitutively active mutants has given an opportunity to study active receptor conformations within acceptable limits using models such as the angiotensin II type 1 (AT1)1 receptor mutant N111G-hAT1 which displays an important constitutive activity. Recently, by using methionine proximity assay, we showed for the hAT1 receptor that TMD III, VI, and VII form the ligand-binding pocket of the C-terminal amino acid of an antagonistic AngII analogue. In the present contribution, we investigated whether the same residues would also constitute the ligand-binding contacts in constitutively activated mutant (CAM) receptors. For this purpose, the same Met mutagenesis strategy was carried out on the N111G double mutants. Analysis of 43 receptors mutants in the N111G-hAT1 series, photolabeled and CNBr digested, showed that there were only subtle structural changes between the wt-receptor and its constitutively active form. 相似文献
7.
Oylum Erkus Victor CL de Jager Maciej Spus Ingrid J van Alen-Boerrigter Irma MH van Rijswijck Lucie Hazelwood Patrick WM Janssen Sacha AFT van Hijum Michiel Kleerebezem Eddy J Smid 《The ISME journal》2013,7(11):2126-2136
Maintenance of a high degree of biodiversity in homogeneous environments is poorly understood. A complex cheese starter culture with a long history of use was characterized as a model system to study simple microbial communities. Eight distinct genetic lineages were identified, encompassing two species: Lactococcus lactis and Leuconostoc mesenteroides. The genetic lineages were found to be collections of strains with variable plasmid content and phage sensitivities. Kill-the-winner hypothesis explaining the suppression of the fittest strains by density-dependent phage predation was operational at the strain level. This prevents the eradication of entire genetic lineages from the community during propagation regimes (back-slopping), stabilizing the genetic heterogeneity in the starter culture against environmental uncertainty. 相似文献
8.
9.
10.
GUILLAUME TCHERKEZ RUDI SCHÄUFELE SALVADOR NOGUÉS CLÉMENT PIEL ARNOUD BOOM GARY LANIGAN CÉCILE BARBAROUX CATARINA MATA SLIMAN ELHANI DEBBIE HEMMING CHRISTINA MAGUAS DAN YAKIR FRANZ W. BADECK HOWARD GRIFFITHS HANS SCHNYDER JALEH GHASHGHAIE 《Plant, cell & environment》2010,33(6):900-913
While there is currently intense effort to examine the 13C signal of CO2 evolved in the dark, less is known on the isotope composition of day‐respired CO2. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure ci/ca effect) from respiratory effect (production of CO2 with a different δ13C value from that of net‐fixed CO2) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO2]. We show that whole mesocosm‐respired CO2 is slightly 13C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly 13C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the 13C abundance in day‐ and night‐evolved CO2. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO2 production may change, thereby explaining the different 12C/13C respiratory fractionations in the light and in the dark. 相似文献