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121.
Neurotransmission requires proper organization of synaptic vesicle pools and rapid release of vesicle contents upon presynaptic depolarization. Genetic studies have begun to reveal a critical role for scaffolding proteins in such processes. Mutations in genes encoding components of the highly conserved MALS/CASK/Mint-1 complex cause presynaptic defects. In all three mutants, neurotransmitter release is reduced in a manner consistent with aberrant vesicle cycling to the readily releasable pool. Recently, liprin-alpha proteins, which define active zone size and morphology, were found to associate with MALS/CASK, suggesting that this complex links the presynaptic release machinery to the active zone, thereby regulating neurotransmitter release. 相似文献
122.
Bożena Szal Agata Jastrzębska Marek Kulka Karolina Leśniak Anna Podgórska Tiit Pärnik Hiie Ivanova Olav Keerberg Per Gardeström Anna M. Rychter 《Planta》2010,232(6):1371-1382
The MSC16 cucumber (Cucumis sativus L.) mitochondrial mutant was used to study the effect of mitochondrial dysfunction and disturbed subcellular redox state
on leaf day/night carbon and nitrogen metabolism. We have shown that the mitochondrial dysfunction in MSC16 plants had no
effect on photosynthetic CO2 assimilation, but the concentration of soluble carbohydrates and starch was higher in leaves of MSC16 plants. Impaired mitochondrial
respiratory chain activity was associated with the perturbation of mitochondrial TCA cycle manifested, e.g., by lowered decarboxylation
rate. Mitochondrial dysfunction in MSC16 plants had different influence on leaf cell metabolism under dark or light conditions.
In the dark, when the main mitochondrial function is the energy production, the altered activity of TCA cycle in mutated plants
was connected with the accumulation of pyruvate and TCA cycle intermediates (citrate and 2-OG). In the light, when TCA activity
is needed for synthesis of carbon skeletons required as the acceptors for NH4
+ assimilation, the concentration of pyruvate and TCA intermediates was tightly coupled with nitrate metabolism. Enhanced incorporation
of ammonium group into amino acids structures in mutated plants has resulted in decreased concentration of organic acids and
accumulation of Glu. 相似文献
123.
124.
Hans Holtan Hans Olav Ibrekk 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》1993,2(2):73-79
General water quality criteria for Norwegian Waters were developed by the State Pollution Control Authority in the earch 1980s. The need for further refinement of these criteria became apparent in the mid-1980s. New water quality criteria were developed in conjunction with the development of a system for assessment of water uses. Two fundamental principles are outlined for determining the classification of water quality in Norway:
- The classification for polluted water. The basis for this system is the natural water quality without any form of influence from man. It is the influence of pollution on the water quality, or the difference between the natural water quality and the water quality today that is classified.
- The system for assessment of water quality for various uses is based both on the existing water quality and some physical and practical properties of the environment. The water quality criteria are specific for various uses.
125.
Basen M Krüger M Milucka J Kuever J Kahnt J Grundmann O Meyerdierks A Widdel F Shima S 《Environmental microbiology》2011,13(5):1370-1379
Anaerobic oxidation of methane (AOM) with sulfate is catalysed by microbial consortia of archaea and bacteria affiliating with methanogens and sulfate-reducing Deltaproteobacteria respectively. There is evidence that methane oxidation is catalysed by enzymes related to those in methanogenesis, but the enzymes for sulfate reduction coupled to AOM have not been examined. We collected microbial mats with high AOM activity from a methane seep in the Black Sea. The mats consisted mainly of archaea of the ANME-2 group and bacteria of the Desulfosarcina-Desulfococcus group. Cell-free mat extract contained activities of enzymes involved in sulfate reduction to sulfide: ATP sulfurylase (adenylyl : sulfate transferase; Sat), APS reductase (Apr) and dissimilatory sulfite reductase (Dsr). We partially purified the enzymes by anion-exchange chromatography. The amounts obtained indicated that the enzymes are abundant in the mat, with Sat accounting for 2% of the soluble mat protein. N-terminal amino acid sequences of purified proteins suggested similarities to the corresponding enzymes of known species of sulfate-reducing bacteria. The deduced amino acid sequence of PCR-amplified genes of the Apr subunits is similar to that of Apr of the Desulfosarcina/Desulfococcus group. These results indicate that the major enzymes involved in sulfate reduction in the Back Sea microbial mats are of bacterial origin, most likely originating from the bacterial partner in the consortium. 相似文献
126.
Heidi K. Grnlien Arne M. Lvlie Olav Sand 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,130(4)
The ciliate Tetrahymena vorax is normally insensitive to light. However, after uptake of acridine orange, blue light evokes instant backward swimming. The dye accumulates mainly in posterior vacuoles, with half-maximal uptake after 1 min. Illumination for 10 s induced a depolarisation of approximately 15 mV lasting less than 2 s, followed by a sustained hyperpolarisation of approximately 20 mV. Deciliated cells displayed a similar response. The hyperpolarisation was linked to reduced membrane resistance, showed a reversal potential of approximately −55 mV and was blocked by 1 mmol l−1 TEA. The rate of rise of electrically evoked Ca2+-spikes was reduced during the hyperpolarisation, which is compatible with elevated cytosolic Ca2+ concentration. This suggests that the hyperpolarisation may be caused by activation of Ca2+-sensitive K+ channels. The depolarisation was abolished in Ca2+-free medium, whereas the hyperpolarisation was unaffected. Illumination for 2 s, or prolonged stimulation restricted to the anterior part of the cell, induced depolarisation only. Illumination of the posterior part caused delayed hyperpolarisation with no preceding depolarisation. We conclude that the induced backward swimming is associated with Ca2+ influx through anterior channels, while Ca2+ released from intracellular stores activates K+ channels responsible for the delayed hyperpolarisation. 相似文献
127.
128.
129.
Torgeir Lund Olav Smidsr d Bj rn Torger Stokke Arnljot Elgsaeter 《Carbohydrate polymers》1988,8(4):245-256
Addition of trivalent chromic ions to xanthan solutions gives rise to gel formation. The dynamic shear storage and loss moduli (0.01 – 10 rad/s) of xanthan solutions with polymer concentrations ranging from 1 to 7 mg/ml and Cr3+ concentrations ranging from 0 to 50 m
have been studied. It is found that the rate of gel formation is strongly dependent on the Cr3+ concentration, but to a much smaller extent on the xanthan concentration. The gelation time is less than 1 h for 50 m
Cr3+ and about 40 h for 2 m
Cr3+. It is found that the minimum Cr3+ concentration needed to give gelation of 1–7 mg/ml xanthan is 1–2 m
. 相似文献
130.
Martin Hartmann Olav B. Holm Gunn A. B. Johansen Gudmund Skjk‐Brk Bjrn T. Stokke 《Biopolymers》2002,63(2):77-88
The enzymes mannuronan C-5 epimerases catalyze conversion of beta-D-mannuronic acid to alpha-L-guluronic acid in alginates at the polymer level and thereby introduce sequences that have functional properties relevant to gelation. The enzymatic conversion by recombinant mannuronan C-5 epimerases AlgE4 and AlgE2 on alginate type substrates with different degree of polymerization and initial low fraction of alpha-L-guluronic acid was investigated. Essentially no enzymatic activity was found for fractionated mannuronan oligomer substrates with an average degree of polymerization, DP(n), less than or equal 6, whereas increasing the DP(n) yielded increased epimerization activity. This indicates that these enzymes have an active site consisting of binding domains for consecutive residues that requires interaction with 7 or more consecutive residues to show enzymatic activity. The experimentally determined kinetics of the reaction, and the residue sequence arrangement introduced by the epimerization, were modeled using Monte Carlo simulation accounting for the various competing intrachain substrates and assuming either a processive mode of action or preferred attack. The comparison between experimental data and simulation results suggests that epimerization by AlgE4 is best described by a processive mode of action, whereas the mode of action of AlgE2 appears to be more difficult to determine. 相似文献