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911.
Ivan Valiela Joseph Costa Kenneth Foreman John M. Teal Brian Howes David Aubrey 《Biodegradation》1999,10(3):177-197
Anthropogenic activities on coastal watersheds increase nutrient concentrations of groundwater. As groundwater travels downslope
it transports these nutrients toward the adjoining coastal water. The resulting nutrient loading rates can be significant
because nutrient concentrations in coastal groundwaters may be several orders of magnitude greater than those of receiving
coastal waters. Groundwater-borne nutrients are most subject to active biogeochemical transformations as they course through
the upper 1 m or so of bottom sediments. There conditions favor anaerobic processes such as denitrification, as well as other
mechanisms that either sequester or release nutrients. The relative importance of advective vs. regenerative pathways of nutrient
supply may result in widely different rates of release of nutrients from sediments. The relative activity of denitrifiers
also may alter the ratio of N to P released to overlying waters, and hence affect which nutrient limits growth of producers.
The consequences of nutrient (particularly nitrate) loading include somewhat elevated nutrient concentrations in the watercolumn,
increased growth of macroalgae and phytoplankton, reduction of seagrass beds, and reductions of the associated fauna. The
decline in animals occurs because of habitat changes and because of the increased frequency of anoxic events prompted by the
characteristically high respiration rates found in enriched waters. 相似文献
912.
In-Young Choi Ivan Tkác Kâmil Ugurbil & Rolf Gruetter 《Journal of neurochemistry》1999,73(3):1300-1308
Using a specific 13C NMR localization method, 13C label incorporation into the glycogen C1 resonance was measured while infusing [1-(13)C]glucose in intact rats. The maximal concentration of [1-(13)C]glycogen was 5.1 +/- 0.6 micromol g(-1) (mean +/- SE, n = 8). During the first 60 min of acute hyperglycemia, the rate of 13C label incorporation (synthase flux) was 2.3 +/- 0.7 micromol g(-1) h(-1) (mean +/- SE, n = 9 rats), which was higher (p < 0.01) than the rate of 0.49 +/- 0.14 micromol g(-1) h(-1) measured > or = 2 h later. To assess whether the incorporation of 13C label was due to turnover or net synthesis, the infusion was continued in seven rats with unlabeled glucose. The rate of 13C label decline (phosphorylase flux) was lower (0.33 +/- 0.10 micromol g(-1) h(-1)) than the initial rate of label incorporation (p < 0.01) and appeared to be independent of the duration of the preceding infusion of [1-(13)C]glucose (p > 0.05 for correlation). The results implied that net glycogen synthesis of approximately 3 micromol g(-1) had occurred, similar to previous reports. When infusing unlabeled glucose before [1-(13)C]glucose in three studies, the rate of glycogen C1 accumulation was 0.46 +/- 0.08 micromol g(-1) h(-1). The results suggest that steady-state glycogen turnover rates during hyperglycemia are approximately 1% of glucose consumption. 相似文献
913.
Hartmut Jahns Rohan Degaonkar Peter Podbevsek Swati Gupta Anna Bisbe Krishna Aluri John Szeto Pawan Kumar Sarah LeBlanc Tim Racie Christopher
R Brown Adam Castoreno Dale
C Guenther Vasant Jadhav Martin
A Maier Janez Plavec Martin Egli Muthiah Manoharan Ivan Zlatev 《Nucleic acids research》2021,49(18):10250
914.
915.
Joanna Jeleska Jiyoung Lee Andrew J. Manning Donald J. Wolfgeher Youngjoo Ahn George Walters-Marrah Ivan E. Lopez Lissette Garcia Sheri A. McClerklin Richard W. Michelmore Stephen J. Kron Jean T. Greenberg 《PLoS pathogens》2021,17(11)
The plant pathogen Pseudomonas syringae secretes multiple effectors that modulate plant defenses. Some effectors trigger defenses due to specific recognition by plant immune complexes, whereas others can suppress the resulting immune responses. The HopZ3 effector of P. syringae pv. syringae B728a (PsyB728a) is an acetyltransferase that modifies not only components of plant immune complexes, but also the Psy effectors that activate these complexes. In Arabidopsis, HopZ3 acetylates the host RPM1 complex and the Psy effectors AvrRpm1 and AvrB3. This study focuses on the role of HopZ3 during tomato infection. In Psy-resistant tomato, the main immune complex includes PRF and PTO, a RIPK-family kinase that recognizes the AvrPto effector. HopZ3 acts as a virulence factor on tomato by suppressing AvrPto1Psy-triggered immunity. HopZ3 acetylates AvrPto1Psy and the host proteins PTO, SlRIPK and SlRIN4s. Biochemical reconstruction and site-directed mutagenesis experiments suggest that acetylation acts in multiple ways to suppress immune signaling in tomato. First, acetylation disrupts the critical AvrPto1Psy-PTO interaction needed to initiate the immune response. Unmodified residues at the binding interface of both proteins and at other residues needed for binding are acetylated. Second, acetylation occurs at residues important for AvrPto1Psy function but not for binding to PTO. Finally, acetylation reduces specific phosphorylations needed for promoting the immune-inducing activity of HopZ3’s targets such as AvrPto1Psy and PTO. In some cases, acetylation competes with phosphorylation. HopZ3-mediated acetylation suppresses the kinase activity of SlRIPK and the phosphorylation of its SlRIN4 substrate previously implicated in PTO-signaling. Thus, HopZ3 disrupts the functions of multiple immune components and the effectors that trigger them, leading to increased susceptibility to infection. Finally, mass spectrometry used to map specific acetylated residues confirmed HopZ3’s unusual capacity to modify histidine in addition to serine, threonine and lysine residues. 相似文献
916.
Ivan N. Rich Irmgard Brackmann Diana Worthington-White Michael J. Dewey 《Journal of cellular physiology》1998,177(1):109-122
The proliferative response of hematopoietic cells is regulated by many factors, including the presence and type of growth factors, the cellular microenvironment, and the physiochemical conditions prevailing in the tissue milieu. A process fundamental to all cells is the regulation of the intracellular acid-base conditions. One of the mechanisms by which intracellular pH (pHi) is regulated is through the sodium/hydrogen exchanger, a ubiquitous membrane protein which exploits the intra- and extracellular sodium ion gradient to drive hydrogen ions out of the cell. However, activation of the exchanger via mitogenic and nonmitogenic signals leads to an increase in pHi which, in turn, may directly or indirectly result in a proliferative response. It has been shown that interaction of fibronectin with its integrin receptor subunits α4 and α5 can result in activation of the Na+/H+ exchanger. In this report, we demonstrate that when mouse bone marrow cells are physically brought together in a preculture system we designate as high cell density culture (HCDC), in a small volume and at the same cellularity as that in the marrow, hematopoietic stem and progenitor cell populations are stimulated with no additional stimulation in the presence of growth factors. Neutralizing antibodies to the growth factors added to HCDC had little, if any, effect on the degree of stimulation. However, when antibodies to fibronectin or the α4 integrin subunit were added to HCDC, inhibition was observed, indicating that the observed hematopoietic stimulation occurred via the fibronectin-integrin pathway. Addition of 5 μM 5-(N,N-hexamethylene) amiloride (5-HMA), a specific inhibitor of the Na+/H+ exchanger, also resulted in inhibition of in vitro hematopoiesis. Since the exchanger was implicated, we then measured the pHi of normal and HCDC-treated bone marrow cells in the absence and presence of 5-HMA by flow cytometry using the fluorescent pH-sensitive indicator, carboxy SNARF-1 AM. It was found that cells subjected to HCDC exhibited a higher pHi than normal fresh cells. In each case, the pHi was lowered in the presence of 5-HMA. Furthermore, addition of antibodies to fibronectin or the α4 integrin subunit to HCDC also reduced the pHi to a similar level to that found for 5-HMA. Our results demonstrate, for the first time, that a hematopoietic stem and progenitor cell proliferative response can be initiated by activation of the Na+/H+ exchanger, leading to an increase in pHi, via cell-cell interaction through the fibronectin-integrin pathway. This pathway could, therefore, be significant not only in normal hematopoietic regulation, but also under pathophysiological conditions. J. Cell. Physiol. 177:109–122, 1998. © 1998 Wiley-Liss, Inc. 相似文献
917.
Both enantiomers of 2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid 2 and 2,4-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid 3 were prepared via resolution of the corresponding racemic carboxylic acids with (R)- and (S)-1-phenylethylamine, respectively. Absolute configuration of (−)-(R)-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid was determined by X-ray crystallography. Curtius rearrangement of acyl azides prepared from enantiomers of these heterocyclic carboxylic acids carried out in benzyl alcohol afforded enantiomers of the corresponding benzyl carbamates, which upon hydrogenolysis gave racemic 2-amino-2-methyl-3,4-dihydro-2H-1,4-benzoxazin-3-one 4 and 2-amino-2,4-dimethyl-3,4-dihydro-2H-1,4h-benzoxazin-3-one 5. Chirality 10:791–799, 1998. © 1998 Wiley-Liss, Inc. 相似文献
918.
Murat Acemoglu Ernst Küsters Jürgen Baumann Ivan Hernandez Ching Pong Mak 《Chirality》1998,10(4):294-306
Various cellulose-2,3-bis-arylcarbamate-6-O-arylesters and cellulose-2,3-bis-arylester-6-O-arylcarbamates, designed to test the possible combined effects of the known tris-arylcarbamate and tris-arylester classes, were synthesized with high regioselectivity at O-C(6), and their use as CSP s in liquid chromatography for enantiomeric separations was investigated. The separations obtained with the synthesized CSP s were compared to the separations achieved on a self-packed reference column, consisting of cellulose-tris-(3,5-dimethylphenyl-carbamate) as CSP standard. Among the synthesized, regioselectively substituted cellulose derivatives, 2,3-bis-O-(3,5-dimethylphenylcarbamate)-6-O-benzoate-cellulose and 2,3-bis-O-(benzoate)-6-O-(3,5-dichlorophenylcarbamate)-cellulose gave the best CSP s for the separation of the test racemates. CSP s from regioselectively substituted cellulose derivatives seem to exhibit higher selectivities than cellulose-tris-(3,5-dimethylphenylcarbamate) for certain classes of racemic compounds. Chirality 10:294–306, 1998. © 1998 Wiley-Liss, Inc. 相似文献
919.
Konstantin S. Boyarshin Anastasia E. Priss Alexsey V. Rayevskiy Mykola M. Ilchenko Igor Ya. Dubey Ivan A. Kriklivyi 《Journal of biomolecular structure & dynamics》2017,35(3):669-682
Aminoacyl tRNA synthetases are enzymes that specifically attach amino acids to cognate tRNAs for use in the ribosomal stage of translation. For many aminoacyl tRNA synthetases, the required level of amino acid specificity is achieved either by specific hydrolysis of misactivated aminoacyl-adenylate intermediate (pre-transfer editing) or by hydrolysis of the mischarged aminoacyl-tRNA (post-transfer editing). To investigate the mechanism of post-transfer editing of alanine by prolyl-tRNA synthetase from the pathogenic bacteria Enterococcus faecalis, we used molecular modeling, molecular dynamic simulations, quantum mechanical (QM) calculations, site-directed mutagenesis of the enzyme, and tRNA modification. The results support a new tRNA-assisted mechanism of hydrolysis of misacylated Ala-tRNAPro. The most important functional element of this catalytic mechanism is the 2′-OH group of the terminal adenosine 76 of Ala-tRNAPro, which forms an intramolecular hydrogen bond with the carbonyl group of the alanine residue, strongly facilitating hydrolysis. Hydrolysis was shown by QM methods to proceed via a general acid-base catalysis mechanism involving two functionally distinct water molecules. The transition state of the reaction was identified. Amino acid residues of the editing active site participate in the coordination of substrate and both attacking and assisting water molecules, performing the proton transfer to the 3′-O atom of A76. 相似文献
920.
Two Radix spp. (Gastropoda: Lymnaeidae) endemic to thermal springs around Lake Baikal represent ecotypes of the widespread Radix auricularia 下载免费PDF全文
Olga Aksenova Maxim Vinarski Ivan Bolotov Alexander Kondakov Yulia Bespalaya Alyona Tomilova Inga Paltser Mikhail Gofarov 《Journal of Zoological Systematics and Evolutionary Research》2017,55(4):298-309
In this study, we re‐examine two species of freshwater gastropods of the genus Radix Montfort, 1810 (family Lymnaeidae), endemic to the geothermal springs in the Lake Baikal region in the southern part of eastern Siberia — Lymnaea (Radix) hakusyensis Kruglov et Starobogatov, 1989, and Lymnaea (Radix) thermobaicalica Kruglov et Starobogatov, 1989. The alleged species status of these endemics has been re‐assessed by means of an integrative approach combining molecular genetic taxonomy techniques with the traditional methods based on shell and soft body morphology. Phylogenetic reconstructions were made using both mitochondrial (COI) and nuclear (ITS2) DNA markers. We used topotypic samples of both species and specimens sampled from other sites around Lake Baikal. The results demonstrate that the two endemic species are only synonyms of a widespread Holarctic species, Radix auricularia (Linnaeus, 1758), and represent its intraspecific morph (ecotype) adapted to living in thermal springs. A new synonymy is proposed: Thermoradix Kruglov et Starobogatov, 1989 = Radix Montfort, 1810 (syn. n.). 相似文献