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21.
We previously demonstrated inhibition of Na+-dependent 32Pi transport in canine renal brush-border membranes in association with NAD+-induced ADP ribosylation of membrane protein(s) and postulated that NAD+ inhibits Pi transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD+ resulted in release of Pi which was prevented by EDTA. It was proposed that NAD+-mediated inhibition of 32Pi transport might occur through this mechanism. To determine whether NAD+ inhibited 32Pi transport by a mechanism other than or in addition to release of Pi, we compared Na+-dependent 32Pi counterflow in brush-border membrane equilibrated with Pi or with Pi generated from NAD+. Release of Pi from NAD+ incubated with brush-border membrane was confirmed. The increased uptake of 32Pi which was demonstrated in brush-border membrane equilibrated with Pi was not measured when intravesicular Pi was generated from a concentration of NAD+ which effected ADP-ribosylation of brush border membranes (100 μM NAD+). In contrast, increased uptake of 32Pi was demonstrated when intravesicular Pi was generated from 1 μM NAD+ which did not effect ADP ribosylation. Mg2+-dependent ADP ribosylation of brush-border membrane incubated with NAD+ was demonstrated which persisted during the time interval of 32Pi uptake measurements. Our findings are compatible with the hypothesis that NAD+-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of Pi transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg2+ and decreased ADP ribosylation. 相似文献
22.
Metabolic acidosis produces a phosphaturia which is independent of parathyroid hormone or dietary phosphorus intake. To study the underlying mechanism, inorganic phosphate (Pi) and glucose transport were studied in brush-border membrane vesicles prepared from the renal cortex of parathyroidectomized rats gavaged for three days with either 7.5 ml of 1.6% NaCl (control) or 1.5% NH4Cl (acidosis). At killing, blood pH and plasma bicarbonate were and , respectively, in control and () and () in acidotic rats. Serum Pi was similar in both groups, while 24 h urine Pi excretion was higher in the acidotic group (). Peak sodium-dependent uptake of Pi, measured after 1.5 min of incubation, was higher in controls than acidotic rats ( vs. protein, ), whereas peak glucose uptake at 1.5 min was not significantly different between the groups. Equilibrium values for Pi and glucose uptake were similar in the two groups. for Pi uptake in the control and acidotic animals were not different, 0.036 and 0.040 mM, respectively. By contrast, was higher in controls than in the acidotic group, 3.13 vs. 1.15 nmol/mg protein per 15 s. These results suggest that metabolic acidosis directly inhibits Pi uptake by the brush border of the proximal tubule by decreasing the availability of Pi carriers of the renal brush-border membrane. 相似文献
23.
The adsorption of 5′-AMP onto precipitated calcium phosphate (CaPi) requires the presence of soluble calcium and this dependence
exhibits a Michaelian-like behavior. This result suggests that the formation of a complex between 5′-AMP and free Ca2+ (CaAMP) is a prelude to the adsorption of the nucleotide in the solid matrix. At concentrations one order of magnitude higher,
Mn2+ and Mg2+ can substitute for soluble Ca2+ in the adsorption of 5′-AMP onto solid CaPi. However, when added simultaneously with 5′-AMP to a heterogeneous mixture that
contains CaPi and soluble Ca2+, Mn2+ and Mg2+ inhibit the adsorption of 5′-AMP in a concentration-dependent manner. This suggests the formation of complexes that are much
less effective for 5′-AMP adsorption than the CaAMP complex. On the other hand, Mn2+ and Mg2+ cannot promote desorption of the nucleotide attached to the precipitate in the presence of soluble Ca2+ if they are added after adsorption has attained equilibrium. Although desorption of 5′-AMP can be obtained by a sequential
dilution of the soluble phase with buffer and no nucleotide in a process that obeys a Langmuir equation, the lack of effect
of Mn2+ or Mg2+ when adsorption has attained its maximal value suggests strong interactions between the CaAMP complex and the solid matrix
when adsorption equilibrium is reached. The divalent cations present in the matrix also participate with different selectivity
in the attachment of the CaAMP complex, indicating that a cation-exchange mechanism could have acted in the modulation of
adsorptive/desorptive processes involving biomonomers and phosphate surfaces in primitive aqueous environments.
Received: 11 December 1995 / Accepted: 5 April 1996 相似文献
24.
Mark O. Johnston Daniel J. Schoen 《Evolution; international journal of organic evolution》1996,50(4):1478-1491
The relation between inbreeding depression and rate of self-fertilization was studied in nine natural populations of the annual genus Amsinckia. The study included two clades (phylogenetic lineages) in which small-flowered, homostylous populations or species are believed to have evolved from large-flowered, heterostylous, self-compatible ones. In one lineage the small-flowered species is tetraploid with disomic inheritance. Rates of self-fertilization were 25% to 55% in the four large-flowered, heterostylous populations; 72% in a large-flowered but homostylous population; and greater than 99.5% in the four small-flowered, homostylous populations, which produce seed autonomously. When present, inbreeding depression occurred in the fertility but not the survival components of fitness. Using a cumulative fitness measure incorporating both survival and fertility (flower number), we found inbreeding depression to be lower in the four very highly self-fertilizing populations than in the five intermediate ones. The Spearman rank correlation between inbreeding depression and selfing rate for the nine populations was –0.50, but was not statistically significant (P = 0.12). Inbreeding depression was greater in the two tetraploid populations than in the very highly self-fertilizing, diploid ones. Phenotypic stability of progeny from self-fertilization tended to be higher in populations with lower inbreeding depression. We conclude that levels of self-fertilization and inbreeding depression in Amsinckia are determined more by other factors than by each other. Estimates of mutation rates and dominance coefficients of deleterious alleles, obtained from a companion study of the four highly self-fertilizing populations, suggest that a strong relationship may not be expected. We discuss the relationship of the present results to current theory of the coevolution of self-fertilization and inbreeding depression. 相似文献
25.
Hyuntae Kim Elaine L. Jacobson Myron K. Jacobson 《Molecular and cellular biochemistry》1994,138(1-2):237-243
NAD glycohydrolases are the longest known enzymes that catalyze ADP-ribose transfer. The function of these ubiquitous, membrane-bound enzymes has been a long standing puzzle. The NAD glycohydrolase are briefly reviewed in light of the discovery by our laboratory that NAD glycohydrolases are bifunctional enzymes that can catalyze both the synthesis and hydrolysis of cyclic ADP-ribose, a putative second messenger of calcium homeostasis.Abbreviations NADase
nicotinamide adenine dinucleotide glycohydrolase
- NAD
nicotinamide adenine dinucleotide
- ADP-ribose
adenosine diphosphoribose
- cADPR
cyclic adenosine diphosphoribose 相似文献
26.
The techniques of 27Al- and 31P-nuclear magnetic resonance (NMR) spectroscopy were used to investigate the interactions of aluminium with intracellular ligands within the mycelium of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton (S238). The vegetative mycelium was grown on medium containing 0.5 mM AlCl3 for 0.5 to 3 d. The 27Al-NMR spectra showed that aluminium was rapidly taken up and accumulated into polyphosphate complexes in the vacuole. Comparison with Al-polyphosphate complexes obtained in vitro on model systems indicated that Al forms at least three mixed-solvation complexes with Pi and polyphosphates, that there is more than one complex present under any set of conditions, and that the equilibrium between these complexes shifts dramatically with Al concentration in the medium. The high phosphate concentrations in the growth medium favoured the accumulation of the Al-polyphosphate complexes. When mycelium containing Al-polyphosphate complexes was transferred to Al-free nutrient solution for 9 d, the Alpolyphosphate complexes were not remobilized. The sequestration of Al in the polyphosphate complexes could therefore make a significant contribution to the protection of mycorrhizal plants against aluminium toxicity.Abbreviations NMR
nuclear magnetic resonance
- PolyP
polyphosphate(s)
- PP1
terminal phosphate of PolyP
- PP3
middle phosphate of PolyP
We thank Prof. Daniel Canet (Laboratoire de Méthodologie RMN, University of Nancy I, Vandceuvre-lès-Nancy, France) for his constant encouragement and Christine Delaruelle for skilled technical assistance in growing the fungal cultures. This work was supported by a research grant from the Commission of the European Communities (STEP-CT90-0059, Role of Ectomycorrhiza in Stress Tolerance of Forest Trees) to F.M. and a travel grant from the Institut National de la Recherche Agronomique to I.K.; R.C. is a recipient of a Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada. 相似文献
27.
Summary Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators
of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern
Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly
interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the
macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine,
aphotic origin of these stromatolites.
Former interpretations of the Posidonien-Schiefer as a shallow-water deposit are mainly based on the occurrence of stromatolites.
We favour the model of a temporarily stagnant, deep, aphotic basin for these planktonrich sediments. Particles resembling
ooids, but lying within mudstones cannot be taken as evidence for shallow agitated water. They either formed within the mud
or are allochthonous.
The deep-water setting of the red limestone of the Alpine Early and Middle Jurassic is indicated by a lack of platform-typical
components like coated grains and phototrophic benthos and by shells of plankton and nekton forming a major part of the sediment.
Stromatolites occur on the steep slope of a drowned Rhaetian reef with an estimated relief of 50–100 m and immediately below
and within radiolarian limestones, deposited below the aragonite compensation depth (ACD).
The aphotic stromatolites show some morphological differences to their shallow water counterparts. In all of our sections
they occurred during intervals of reduced sedimentation. They form only thin horizons and probably grew very slowly. Mineralizations
by Fe−Mn oxides and phosphate are very common. The presence of a microbial film is evident from binding of sedimentary particles,
but the nature of the microbes is not known. Growth habits within the very distinct environments of red limestone and black
shales show some common features, but also clear differences.
The microproblematicumFrutexites
Maslov is a very common component in deep-water stromatolites, but may also itself form small crusts or dendrolites. It occurs in
two different forms. Opaque, slender forms with indistinct outlines probably grew within the weakly lithified sediment. Thicker,
transparent forms with well defined outlines are found in cavities and probably also grew on the seafloor. Well preserved
specimens display an internal fabric of radially arranged fibres of Fe−Mn oxides and calcite. It is suggested that calcite
or aragonite were one original mineralogy ofFrutexites, which was later replaced by Fe−Mn oxides or phosphate.
It is not certain whetherFrutexites is an organic, biomineralized structure or an inorganic mineralization, but the variable mineralogy and growth forms in different
environments point to an organic origin. But even if organic, the occurrence in cryptic habitats and negative phototactic
growth-directions make it clear thatFrutexites was not phototrophic. 相似文献
28.
Stephen D. Bird Robert J. Walker Michael J. Hubbard 《In vitro cellular & developmental biology. Animal》1994,30(7):420-424
Summary The effect of a conventional antibiotic (penicillin/streptomycin) mixture on the widely used kidney epithelial cell line,
LLC-PK1, was investigated by measuring growth and intracellular free calcium. Free calcium concentration was the same in cells cultured
for 3 to 7 wk with (“plus”) and without (“minus”) antibiotics both at rest and when challenged with high (14 mM) external calcium. When exposed to vasopressin, minus cells exhibited significantly smaller calcium transients than plus
cells. A similar difference existed for transients elicited by a calcium ionophore, 4-br-A23187. After longer periods of culture
(>20 wk), minus cells grew slower than plus cells but on reaching confluence (minus cells took 1 day longer) the morphologies
and viabilities were indistinguishable. The finding that culture with penicillin/streptomycin reversibly modified some properties
of LLC-PK1 cells, at least partly through altered calcium homeostasis, is of importance for workers using this cell model to study drug
effects and raises the general possibility of similar effects on other cultured cells. 相似文献
29.
Huan Chen Qiujun Lin Zhuo Li Jin Chu Hai Dong Qiong Mei Yuanhu Xuan 《Molecular Plant Pathology》2023,24(3):221-231
Sheath blight (ShB) severely threatens rice cultivation and production; however, the molecular mechanism of rice defence against ShB remains unclear. Screening of transposon Ds insertion mutants identified that Calcineurin B-like protein-interacting protein kinase 31 (CIPK31) mutants were more susceptible to ShB, while CIPK31 overexpressors (OX) were less susceptible. Sequence analysis indicated two haplotypes of CIPK31: Hap_1, with significantly higher CIPK31 expression, was less sensitive to ShB than the Hap_2 lines. Further analyses showed that the NAF domain of CIPK31 interacted with the EF-hand motif of respiratory burst oxidase homologue (RBOHA) to inhibit RBOHA-induced H2O2 production, and RBOHA RNAi plants were more susceptible to ShB. These data suggested that the CIPK31-mediated increase in resistance is not associated with RBOHA. Interestingly, the study also found that CIPK31 interacted with catalase C (CatC); cipk31 mutants accumulated less H2O2 while CIPK31 OX accumulated more H2O2 compared to the wild-type control. Further analysis showed the interaction of the catalase domain of CatC with the NAF domain of CIPK31 by which CIPK31 inhibits CatC activity to accumulate more H2O2. 相似文献
30.