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Steady state kinetics were used to examine the influence of Cd2+ both on K+ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K+(86Rb+) uptake in intact or excised beet roots. The in vitro effect of Cd2+ was studied both on a 12000–25000 g root fraction of the (Na++K++Mg2+)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd2+ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd2+ at concentrations <100 μM inhibits the specific K+ activation at both high and low affinity sites for K+. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K+ <5 mM, the inhibition by Cd2+ with respect to K+ is uncompetitive. In the presence of MgATP and K+ >10 μM, the inhibition by Cd2+ is competitive. 3) At the low concentrations of K+, Cd2+ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K+(86Rb+) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K+(86Rb+) uptake is little influenced by Cd2+. As Cd2+ inhibits the metabolic uptake of K+(86Rb+) and the K+ activation of the ATPase in the same way at low concentrations of K+, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K+ is low, the presence of Cd2+ could be disadvantageous. 相似文献
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Abstract A new species, Sinophasma largum sp. nov., is described from China (Sichuan, Guizhou, Hunan, Hubei and Guangxi Provinces). The type specimens are kept in the Institute of Zoology, Academia Sinica. 相似文献
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SYLVIA LINDBERG 《Physiologia plantarum》1980,48(1):65-70
A microsomal (Na++ K++ Mg2+)ATPase preparation from sugar beet roots was used. The activation by simultaneous addition of Na+ and K+ at different levels was examined in terms of steady state kinetics. The observed data can be summarized in the following way: 1. The apparent affinity between the enzyme and the substrate MgATP depends on the ratio between Na+ and K+. At low Na+ concentration (below 5 mM), the apparent Km decreases with increasing concentrations of K+ (1–20 mM). At 5 mM Na+, the K+ level does not change the apparent Km, while at Na+ levels above 10 mM, the apparent Km between enzyme and substrate increases with increasing concentration of K+. 2. When the MgATP concentration is kept constant, homotropic cooperativity (concerning one type of ligand) and heterotropic cooperativity (concerning different types of ligands) exist in the activation by Na+ and K+. The Na+ binding is cooperative with different Km values and Hill coefficients (n) in the presence of low and high concentration of K+. At low Na+ level (< 5 mM). a negative cooperativity exists for Na+ (nNa < 1) which is more pronounced in the presence of high [K+]. When the concentration of Na+ is raised the negative cooperativity disappears and turns into a positive one (nNa > 1). Only K+ binding in the presence of low [Na+] shows cooperativity with a Hill coefficient that reflects changes from negative to positive homotropic cooperativity with increasing concentrations of K+ (nK < 1 → nK > 1). In the presence of [Na+] > 10 mM, the changes in nk are insignificant. 3. A model is proposed in which one or two different K sites and one or two Na sites control the catalytic activity, with multiple interactions between Na+, K+ and MgATP. 4. In the presence of Na+ (< 10 mM), K+ is probably bound to two K sites, one of which translocates K+ through the membrane by an antiport Na+/K+ mechanism. This could be connected with an elevated K+ uptake in the presence of Na+ and could therefore explain some field properties of sugar beets. 相似文献
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Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd2+ was excreted by plants exposed for 1–10 days to 9 or 45 μ M Cd2+ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na+ and Cl− was positively correlated with NaCl concentration (1.5, 10, 50 m M ) of the medium. The Na+ /Cl− ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca2+ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K+ and Mg2+ was only little affected by NaCl. Excretion of Li+ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li+ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla . 相似文献
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Alberta Leon Laura Facci Gino Toffano Sandro Sonnino Guido Tettamanti 《Journal of neurochemistry》1981,37(2):350-357
GM1 ganglioside binding to the crude mitochondrial fraction of rat brain and its effect on (Na+, K+)-ATPase were studied, the following results being obtained: (a) the binding process followed a biphasic kinetics with a break at 50 nM-GM1; GM1 at concentrations below the break was stably associated, while over the break it was loosely associated; (b) stably bound GM1 activated (Na+, K+)-ATPase up to a maximum of 43%; (c) the activation was dependent upon the amount of bound GM1 and was highest at the critical concentration of 20 pmol bound GM1 X mg protein-1; (d) loosely bound GM1 suppressed the activating effect on (Na+, K+)-ATPase elicited by firmly bound GM1; (e) GM1-activated (Na+, K+)-ATPase had the same pH optimum and apparent Km (for ATP) as normal (Na+, K+)-ATPase but a greater apparent Vmax; (f) under identical binding conditions (2 h, 37 degrees C, with 40 nM substance) all tested gangliosides (GM1, GD1a, GD1b, GT1b) activated (Na+, K+)-ATPase (from 26-43%); NeuNAc, sodium dodecylsulphate, sulphatide and cerebroside had only a very slight effect. It is suggested that the ganglioside activation of (Na+-K+)-ATPase is a specific phenomenon not related to the amphiphilic and ionic properties of gangliosides, but due to modifications of the membrane lipid environment surrounding the enzyme. 相似文献
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Sune Pettersson 《Physiologia plantarum》1981,52(4):431-436
Passive fluxes of K+ (86 Rb) into roots of sunflower ( Helianthus annuus L. cv. Uniflorus) were determined at low K+ concentration (0.1 and 1.0 mM K+ ) in the ambient solution. Metabolic uptake of K+ was inhibited by 10−4 M 2,4-dinitrophenol (DNP). K+ (86 Rb) fluxes were studied both continuously and by time differentiation of uptake. In high K+ roots passive uptake was directly proportional to the K+ concentration of the uptake solution, indicating free diffusion. This assumption was supported by the fact that passive Rb+ uptake was not affected by high K+ concentrations. In low K+ roots the passive uptake of K+ was higher than in high K+ roots. The increase was possibly due to carrier-mediated K+ transport. As K+ effluxes were quantitatively similar to influxes, it is suggested that passive K+ fluxes represent exchange diffusion without relation to net K+ transport. 相似文献
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Sylvia Lindberg 《Physiologia plantarum》1990,79(2):275-282
Three cultivars of sugar beet (Beta vulgaris L.), which are sensitive to aluminium (Al) in the order Primahill > Monohill > Regina, were grown in water culture for 2 weeks. Nutrients were supplied at 15% increase of amounts daily, corresponding to the nutrient demand for maximal growth. The 2.4-dinitrophenol (DNP)-sensitive (metabolic) and DNP-insensitive (non-metabolic) uptake of aluminium, phosphate. 45Ca2+ and K+(86Rb+) in roots were measured as well as transport to shoots of intact plants. All 3 cultivars absorbed more aluminium if DNP was present during the aluminium treatment than in its absence. It is suggested that sugar beets are able to extrude aluminium activity or that they possess an active mechanism to keep Al outside the cell. The presence of Al in the medium during the 1-h experiment affected the metabolic and non-metabolic fluxes of 45Ca2+ and K+(86Rb+) in different ways. In the presence of DNP, the influx of both 45Ca2+ and K+(86Rb+) and the efflux of 45Ca2+ were inhibited by Al in a competitive way. At inhibition of 45Ca2+ influx, 2 Al ions are probably bound per Ca2+ uptake site in cv. Regina (Al-tolerant), but in cvs Primahill and Monohill only one Al ion is bound (more Al sensitive). Aluminium competitively inhibited the active efflux of 45Ca2+ (absence of DNP) in almost the same way in the 3 cultivars. In contrast, aluminium stimulated the influx of K+(86Rb+) in cvs Primahill, Monohill and Regina in the absence of DNP. Thus, the Al effects on active and passive K+(86Rb+) influx are different. The total influx of K+(86Rb+) increased in the presence of Al and might be connected to an active exclusion of Al. Regina is the least Al-sensitive cultivar, probably because Al interferes less with the Ca2+ fluxes and because this cultivar actively excludes phosphate in the presence of Al. Thus Al-phosphate precipitation within the plant could be avoided. 相似文献
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R. H. Jongbloed J. M. A. M. Clement G. W. F. H. Borst-Pauwels 《Physiologia plantarum》1991,83(3):427-432
NH4+ and K+ uptake experiments have been conducted with 3 ectomycorrhizal fungi, originating from Douglas fir (Pseudotsuga menziesii (Mirb.] Franco) stands. At concentrations up to 250 μM, uptake of both NH4+ and K+ follow Michaelis-Menten kinetics. Laccaria bicolor (Maire) P. D. Orton, Lactarius rufus (Scop.) Fr. and Lactarius hepaticus Plowr. ap. Boud. exhibit Km values for NH4+ uptake of 6, 35, and 55 μM, respectively, and Km values for K+ uptake of 24, 18, and 96 μM, respectively. Addition of 100 μM NH4+ raises the Km of K+ uptake by L. bicolor to 35 μM, while the Vmax remains unchanged. It is argued that the increase of Km is possibly caused by depolarization of the plasma membrane. It is not due to a competitive inhibition of K+ by NH4+ since the apparent inhibitor constant is much higher than the Km, for NH4+ uptake. The possibility that NH4+ and K+ are taken up by the same carrier can be excluded. The Km, values for K+ uptake in the two other fungi are not significantly affected by 100 μM NH4+. Except for a direct effect of NH4+ on influx of K+ into the cells, there may also be an indirect effect after prolonged incubation of the cells in the presence of 100 μM NH4+. 相似文献
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Stephen J. Bunn Alistair T. R. Sim Lynn M. Herd Leone M. Austin Peter R. Dunkley 《Journal of neurochemistry》1995,64(3):1370-1378
Abstract: Tyrosine hydroxylase (TOH), the rate-limiting enzyme in catecholamine biosynthesis, is regulated by phosphorylation. Activation of histaminergic H1 receptors on cultured bovine adrenal chromaffin cells stimulated a rapid increase in TOH phosphorylation (within 5 s) that was sustained for at least 5 min. The initial increase in TOH phosphorylation (up to 1 min) was essentially unchanged by the removal of extracellular Ca2+ . In contrast, the H1 -mediated response was abolished by preloading the cells with BAPTA acetoxymethyl ester (50 µ M ) and significantly reduced by prior exposure to caffeine (10 m M for 10 min) to deplete intracellular Ca2+ . Trypticphosphopeptide analysis by HPLC revealed that the H1 response in the presence or absence of extracellular Ca2+ resulted in a major increase in the phosphorylation of Ser19 with smaller increases in that of Ser40 and Ser31 . In contrast, although a brief stimulation with nicotine (30 µ M for 60 s) also resulted in a major increase in Ser19 phosphorylation, this response was abolished in the absence of extracellular Ca2+ . These data indicate that the mobilization of intracellular Ca2+ plays a crucial role in supporting H1 -mediated TOH phosphorylation and may thus have a potentially important role in regulating catecholamine synthesis. 相似文献
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Two monovalent ion porters, the putative Na+/H+ antiporter (NapA) of Enterococcus hirae and the putative K+/H+ antiporter (KefC) of Escherichia coli, are similar in sequence throughout their hydrophobic domains. These two proteins, which comprise a novel family of transporters unrelated to the previously characterized Na+/H+ exchangers of E. coli (NhaA and NhaB) are proposed to function by essentially the same mechanism. 相似文献
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R. L. TAYLOR JR. R. A. CLARE P. H. WARD R. W. BRILES† W. E. BRILES† 《Animal genetics》1988,19(3):277-284
Responses to Rous sarcoma virus (RSV) induced tumours were studied in UNH 105, a non-inbred line of New Hampshire chickens. Six single male matings encompassing a total of 50 dams produced 345 progeny which segregated for B complex genotypes B23/B23, B23/B24, B23/B30, B24/B24, B24/B30 and B30/B30. Six-week-old chicks were wingweb inoculated with a pseudotype of Bryan high titre Rous sarcoma virus, BH RSV (RAV-1). Tumours were scored for size six times over a 10-week period post-inoculation. Each chick was assigned a tumour profile index (TPI) as an indicator of immunological response. The number of days to death (DTD) was recorded for 148 chicks with terminal tumours. Genotypes B23/B23, B23/B24 and B23/B30, with TPIs of 1.8, 1.7 and 2.0 respectively, did not differ significantly from each other, suggesting dominance of response of B23 over B24 and B30 haplotypes. B24/B30 chicks with the highest TPI (3.4) and shortest DTD (34.6) were significantly different from B30/B30 (2.8; 41.6) but not from B24/B24 (3.1; 34.9) suggesting dominance of response of the B24 haplotype over B30 in the absence of B23. 相似文献