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901.
The regulation of cytosolic Ca2+ has been investigated in growing root-hair cells of Sinapis alba L. with special emphasis on the role of the plasmamembrane Ca2+-ATPase. For this purpose, erythrosin B was used to inhibit the Ca2+-ATPase, and the Ca2+ ionophore A23187 was applied to manipulate cytosolic free [Ca2+] which was then measured with Ca2+-selective microelectrodes. (i) At 0.01 M, A23187 had no effect on the membrane potential but enhanced the Ca2+ permeability of the plasma membrane. Higher concentrations of this ionophore strongly depolarized the cells, also in the presence of cyanide. (ii) Unexpectedly, A23187 first caused a decrease in cytosolic Ca2+ by 0.2 to 0.3 pCa units and a cytosolic acidification by about 0.5 pH units, (iii) The depletion of cytosolic free Ca2+ spontaneously reversed and became an increase, a process which strongly depended on the external Ca2+ concentration, (iv) Upon removal of A23187, the cytosolic free [Ca2+] returned to its steady-state level, a process which was inhibited by erythrosin B. We suggest that the first reaction to the intruding Ca2+ is an activation of Ca2+ transporters (e.g. ATPases at the endoplasmic reticulum and the plasma membrane) which rapidly remove Ca2+ from the cytosol. The two observations that after the addition of A23187, (i) Ca2+ gradients as steep as-600 mV could be maintained and (ii) the cytosolic pH rapidly and immediately decreased without recovery indicate that the Ca2+-exporting plasma-membrane ATPase is physiologically connected to the electrochemical pH gradient, and probably works as an nH+/Ca2+-ATPase. Based on the finding that the Ca2+-ATPase inhibitor erythrosin B had no effect on cytosolic Ca2+, but caused a strong Ca2+ increase after the addion of A23187 we conclude that these cells, at least in the short term, have enough metabolic energy to balance the loss in transport activity caused by inhibition of the primary Ca2+-pump. We further conclude that this ATPase is a major Ca2+ regulator in stress situations where the cytosolic Ca2+ has been shifted from its steady-state level, as may be the case during processes of signal transduction.Abbreviations and Symbols EB
erythrosin B
- Em
membrane potential
- pCa
negative logarithm of the Ca2+ concentration
This work was supported by the Deutche Forschungsgemeinschaft (H.F.) and the Alexander-von-Humboldt-Foundation (A.T.). 相似文献
902.
Formation and Action of Lignin-Modifying Enzymes in Cultures of Phlebia radiata Supplemented with Veratric Acid 总被引:2,自引:2,他引:0
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Taina Lundell Andrzej Leonowicz Jerzy Rogalski Annele Hatakka 《Applied microbiology》1990,56(9):2623-2629
Transformation of veratric (3,4-dimethoxybenzoic) acid by the white rot fungus Phlebia radiata was studied to elucidate the role of ligninolytic, reductive, and demeth(ox)ylating enzymes. Under both air and a 100% O2 atmosphere, with nitrogen limitation and glucose as a carbon source, reducing activity resulted in the accumulation of veratryl alcohol in the medium. When the fungus was cultivated under air, veratric acid caused a rapid increase in laccase (benzenediol:oxygen oxidoreductase; EC 1.10.3.2) production, which indicated that veratric acid was first demethylated, thus providing phenolic compounds for laccase. After a rapid decline in laccase activity, elevated lignin peroxidase (ligninase) activity and manganese-dependent peroxidase production were detected simultaneously with extracellular release of methanol. This indicated apparent demethoxylation. When the fungus was cultivated under a continuous 100% O2 flow and in the presence of veratric acid, laccase production was markedly repressed, whereas production of lignin peroxidase and degradation of veratryl compounds were clearly enhanced. In all cultures, the increases in lignin peroxidase titers were directly related to veratryl alcohol accumulation. Evolution of 14CO2 from 3-O14CH3-and 4-O14CH3-labeled veratric acids showed that the position of the methoxyl substituent in the aromatic ring only slightly affected demeth(ox)ylation activity. In both cases, more than 60% of the total 14C was converted to 14CO2 under air in 4 weeks, and oxygen flux increased the degradation rate of the 14C-labeled veratric acids just as it did with unlabeled cultures. 相似文献
903.
Andrzej Kraszewski Maria A. Stuchly Stanislaw S. Stuchly Andrew M. Smith 《Bioelectromagnetics》1982,3(4):421-432
An open-ended coaxial line and an improved measurement method employing a computer controlled network analyzer were used to measure the permittivity of cat tissues. Muscle, spleen, kidney cortex, liver,and brain cortex were measured in vivo and in vitro at frequencies between 100 MHz and 8 GHz. The differences between the permittivities of these cat tissues, in the aforementioned range of frequencies, when measured in vivo and a few (up to four) hours after death, were found to be within the experimental uncertainty. 相似文献
904.
Recent work has shown that a short α-helix can be stable in water near 1 °C when stabilized by specific interactions between side-chains, while earlier “host-guest” results with random copolymers have shown that a short α-helix is unstable in water at all temperatures in the absence of stabilizing side-chain interactions. As regards the mechanism of protein folding, it is now reasonable on energetic grounds to consider isolated α-helices and β-sheets as the first intermediates on the pathway of protein folding. Proton nuclear magnetic resonance is used here to detect isolated secondary structures in ribonuclease A denatured by guanidine · HCl (GuHCl). Temperatures near 1 °C are used because the low-temperature stability of the C-peptide helix may be a general property of isolated secondary structures in water.Our procedure is to titrate with GuHCl the C2H resonance lines of the four histidine residues of denatured ribonuclease A. Studies of model peptides (C-peptide (lactone) and C-peptide carboxylate, residues 1 to 13 of ribonuclease A; S-peptide, residues 1 to 20) show linear titration curves for the C2H resonance of His12 above 0.5 M-GuHCl, once helix unfolding is complete. Deviations from this line are used to monitor helix formation. The GuHCl titration curves of the other three histidine residues are also linear, once unfolding is complete. The results show that the helix found in C-peptide and S-peptide is also found in denatured ribonuclease A, where it behaves as an isolated helix not stabilized significantly by interactions with other chain segments. Studies of denatured S-protein show that the remaining three His residues, His48, His105 and His119, are involved in structure only below 1 m-GuHCl at 9 °C, pH 1.9. The nature of this structure is not known. The main conclusion from this work is that the His12 helix can be observed as a stable, isolated helix in denatured ribonuclease A near 1 °C, and that none of the other three His residues is involved in a comparably stable local structure. In native ribonuclease A, His12 is within an α-helix and the other three His residues are involved in a 3-stranded β-sheet structure.The helix-coil transition of C-peptide has also been studied for other side-chain resonances by GuHCl titration. Typically, but not always, the titration curves are linear after helix unfolding takes place and resonance lines from different residues of the same amino acid type can be resolved in GuHCl solutions. This is true of the four histidine residues of ribonuclease A although their pK values in 5 m-GuHCl are nearly the same. In C-peptide, the βCH3 resonance of Ala6 is affected strongly by GuHCl while the lines of Ala4 and Ala5 are shifted only weakly by GuHCl. Evidently the interactions between GuHCl and side-chains in an unfolded peptide depend upon neighboring groups. 相似文献
905.
Effects of Septal Lesions on Enzymes of Acetyl-CoA Metabolism in the Cholinergic System of the Rat Hippocampus 总被引:4,自引:4,他引:0
Andrzej Szutowicz Paul A. Srere Charles N. Allen Isaac L. Crawford 《Journal of neurochemistry》1982,39(2):458-463
Abstract: Electrolytic lesions made in the medial septum of the rat brain caused an 80% decrease in the activity of choline acetyltransferase and a 33% reduction in ATP-citrate lyase activity in the synaptosomal fraction from the hippocampus. Decreases in the activities of the two enzymes in the cytosol (S3 ) fraction were 70 and 13%, respectively. The activities of pyruvate dehydrogenase, citrate synthase, acetyl-CoA synthase, and carnitine acetyltransferase in crude hippocampal homogenates and in subcellular fractions were not affected by septal lesions. The data indicate that ATP-citrate lyase is linked to the septal-hippocampal pathway and that the enzyme is preferentially located in cholinergic nerve endings that terminate within the hippocampus. 相似文献
906.
907.
Céline Roques Yan Coulombe Mathieu Delannoy Julien Vignard Simona Grossi Isabelle Brodeur Amélie Rodrigue Jean Gautier Alicja Z Stasiak Andrzej Stasiak Angelos Constantinou Jean‐Yves Masson 《The EMBO journal》2009,28(16):2400-2413
Monoubiquitination of the Fanconi anaemia protein FANCD2 is a key event leading to repair of interstrand cross‐links. It was reported earlier that FANCD2 co‐localizes with NBS1. However, the functional connection between FANCD2 and MRE11 is poorly understood. In this study, we show that inhibition of MRE11, NBS1 or RAD50 leads to a destabilization of FANCD2. FANCD2 accumulated from mid‐S to G2 phase within sites containing single‐stranded DNA (ssDNA) intermediates, or at sites of DNA damage, such as those created by restriction endonucleases and laser irradiation. Purified FANCD2, a ring‐like particle by electron microscopy, preferentially bound ssDNA over various DNA substrates. Inhibition of MRE11 nuclease activity by Mirin decreased the number of FANCD2 foci formed in vivo. We propose that FANCD2 binds to ssDNA arising from MRE11‐processed DNA double‐strand breaks. Our data establish MRN as a crucial regulator of FANCD2 stability and function in the DNA damage response. 相似文献
908.
909.
Magdalena Frańska Dobrochna Ginter-Kramarczyk Andrzej Szymański Tomasz Kozik Rafał Frański 《International biodeterioration & biodegradation》2009,63(8):1066-1069
Biodegradation of a commercially available mixture of octylphenol ethoxylates (Triton X-100) under the condition of OECD 301E screening test was studied by using electrospray ionisation mass spectrometry. It was found that ethoxylate containing six ethoxylene units (OPEO6) is more resistant to the biodegradation process than other ethoxylates (e.g. than OPEO5 and OPEO7). After 40 days of biodegradation process the signal of OPEO6 was clearly seen, but signals of OPEO5 and OPEO7 were not detected. After 40 days, all OPEOn with n > 4 were converted into carboxylated derivatives. Carboxylated derivatives were observed in negative ion mode as OPEOn-CH2COO? ions. Biodegradation of OPEO5-CH2COOH (carboxylated derivative correspondent of OPEO6) occurred slower than biodegradation of the others, as resulted from obtained ESI mass spectra. 相似文献
910.
Ips typographus (Col., Curculionidae, Scolytinae) occurring on Picea abies stems is a species characterised by large fluctuations in population numbers and causing frequent outbreaks. In protected areas, I. typographus is regarded as a sensitive bioindicator responsive to changes in forest health and vitality. In conservation-oriented forestry, attention is being paid to the ecological value of I. typographus beetles as ecosystem engineers and keystone species, driving forest natural regeneration and conversion. Despite many publications devoted to I. typographus, no accurate method for estimating the population density of this species has been developed. The objective of this study was to develop a statistical method for estimating I. typographus population density that enables calculation of estimation errors. The proposed method consists of two parts: tree-level analyses and stand-level analyses. Part one allows calculation of the total density of I. typographus infestation of each of P. abies selected stem (after selecting sample windfalls), part two allows estimation of the mean total infestation density of the stem in the area investigated. Linear regression functions were applied to part one and survey sampling to part two. The method is only marginally invasive because it involves debarking of one 0.5 m-long stem section on maximum 50 P. abies windfalls (trap trees can optionally be used). The developed method was employed to assess I. typographus population density in the ?wi?tokrzyskie Mountains in Central Poland in an area of ca. 4,000 ha. In 2010, in the area investigated, the mean total I. typographus infestation density of the P. abies stem was 440.6 maternal galleries/m2 (from 358.7 to 522.6 maternal galleries/m2 with ?? = 0.05; the relative error of estimation was 18.6%). The examined I. typographus population was in a progradation phase. The proposed method can be used in nature reserves, national parks and managed forests, mainly for scientific purposes. 相似文献