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排序方式: 共有633条查询结果,搜索用时 16 毫秒
91.
92.
Upregulation of bundle sheath electron transport capacity under limiting light in C4 Setaria viridis
Maria Ermakova Chandra Bellasio Duncan Fitzpatrick Robert T. Furbank Fikret Mamedov Susanne von Caemmerer 《The Plant journal : for cell and molecular biology》2021,106(5):1443-1454
C4 photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO2 concentration at the site of CO2 fixation. C4 plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity. Plants grown under low light (LL) maintained CO2 assimilation rates similar to high light plants but had an increased chlorophyll and light-harvesting-protein content, predominantly in BS cells. Photosystem II (PSII) protein abundance, oxygen-evolving activity and the PSII/PSI ratio were enhanced in LL BS cells, indicating a higher capacity for linear electron flow. Abundances of PSI, ATP synthase, Cytochrome b6f and the chloroplast NAD(P)H dehydrogenase complex, which constitute the BS cyclic electron flow machinery, were also increased in LL plants. A decline in PEP carboxylase activity in mesophyll cells and a consequent shortage of reducing power in BS chloroplasts were associated with a more oxidised plastoquinone pool in LL plants and the formation of PSII – light-harvesting complex II supercomplexes with an increased oxygen evolution rate. Our results suggest that the supramolecular composition of PSII in BS cells is adjusted according to the redox state of the plastoquinone pool. This discovery contributes to the understanding of the acclimation of PSII activity in C4 plants and will support the development of strategies for crop improvement, including the engineering of C4 photosynthesis into C3 plants. 相似文献
93.
Rajan Kumar Choudhary Vikrant Quadir M. Siddiqui Pankaj S. Thapa Sweta Raikundalia Nikhil Gadewal 《Journal of biomolecular structure & dynamics》2016,34(7):1533-1544
BARD1–BRCA1 complex plays an important role in DNA damage repair, apoptosis, chromatin remodeling, and other important processes required for cell survival. BRCA1 and BARD1 heterodimer possess E3 ligase activity and is involved in genome maintenance, by functioning in surveillance for DNA damage, thereby regulating multiple pathways including tumor suppression. BRCT domains are evolutionary conserved domains present in different proteins such as BRCA1, BARD1, XRCC, and MDC1 regulating damage response and cell-cycle control through protein–protein interactions. Nonetheless, the role of BARD1BRCT in the recruitment of DNA repair mechanism and structural integrity with BRCA1 complex is still implicit. To explicate the role of BARD1BRCT in the DNA repair mechanism, in silico, in vitro, and biophysical approach were applied to characterize BARD1 BRCT wild-type and Arg658Cys and Ile738Val mutants. However, no drastic secondary and tertiary structural changes in the mutant proteins were observed. Thermal and chemical denaturation studies revealed that mutants Arg658Cys and Ile738Val have a decrease in Tm and ?G than the wild type. In silico studies of BARD1 BRCT (568-777) and mutant protein indicate loss in structural compactness on the Ile738Val mutant. Comparative studies of wild-type and mutants will thus be helpful in understanding the basic role of BARD1BRCT in DNA damage repair. 相似文献
94.
95.
Witold A. Witkowski Jeanne A. Hardy 《Protein science : a publication of the Protein Society》2009,18(7):1459-1468
The active sites of caspases are composed of four mobile loops. A loop (L2) from one half of the dimer interacts with a loop (L2′) from the other half of the dimer to bind substrate. In an inactive form, the two L2′ loops form a cross‐dimer hydrogen‐bond network over the dimer interface. Although the L2′ loop has been implicated as playing a central role in the formation of the active‐site loop bundle, its precise role in catalysis has not been shown. A detailed understanding of the active and inactive conformations is essential to control the caspase function. We have interrogated the contributions of the residues in the L2′ loop to catalytic function and enzyme stability. In wild‐type and all mutants, active‐site binding results in substantial stabilization of the complex. One mutation, P214A, is significantly destabilized in the ligand‐free conformation, but is as stable as wild type when bound to substrate, indicating that caspase‐7 rests in different conformations in the absence and presence of substrate. Residues K212 and I213 in the L2′ loop are shown to be essential for substrate‐binding and thus proper catalytic function of the caspase. In the crystal structure of I213A, the void created by side‐chain deletion is compensated for by rearrangement of tyrosine 211 to fill the void, suggesting that the requirements of substrate‐binding are sufficiently strong to induce the active conformation. Thus, although the L2′ loop makes no direct contacts with substrate, it is essential for buttressing the substrate‐binding groove and is central to native catalytic efficiency. 相似文献
96.
97.
98.
Vitaly N. Nikandrov Oleg N. Murashko Galina V. Vorobyova Nelly S. Pyzhova Natalie V. Kvyatkovskaya Oksana A. Bartalevich 《International journal of peptide research and therapeutics》1997,4(4-6):497-502
Summary The formation of stable equimolar complexes of streptokinase or plasminogen with muscle lactate dehydrogenase or pyruvate
kinase, heart mitochondrial malate dehydrogenase and hepatic catalase at pH 7.4, 3.0 and 10.0 was first detected by differential
spectroscopy methods. All complexes, except those of plasminogen with dehydrogenases, were resistant to 6 M urea. Judging
from circular dichroism spectra, tertiary and secondary structures were considerably changed in the complexes. These changes
were significantly dependent upon the nature of interacting proteins; in some cases their structures were more ordered. NAD
(but not NADH) hampered the formation of streptokinase complexes with dehydrogenases. The plasminogen-activating function
of streptokinase and the ability of plasminogen to be activated by streptokinase in the complexes with oxidoreductases were
essentially unchanged. Pyruvate kinase induced a moderate (by 35%) increase in the streptokinase activating function. It is
assumed that the formation of complexes of streptokinase or plasminogen with enzymes may serve as a link in metabolic regulation
and/or intercellular interactions. 相似文献
99.
THE ROLE OF PERIPHYTON IN PHOSPHORUS RETENTION IN SHALLOW FRESHWATER AQUATIC SYSTEMS 总被引:7,自引:0,他引:7
Walter K. Dodds 《Journal of phycology》2003,39(5):840-849
Eutrophication caused by phosphorus (P) leads to water quality problems in aquatic systems, particularly freshwaters, worldwide. Processing of nutrients in shallow habitats removes P from water naturally and periphyton influences P removal from the water column in flowing waters and wetlands. Periphyton plays several roles in removing P from the water column, including P uptake and deposition, filtering particulate P from the water, and attenuating flow, which decreases advective transport of particulate and dissolved P from sediments. Furthermore, periphyton photosynthesis locally increases pH by up to 1 unit, which can lead to increased precipitation of calcium phosphate, concurrent deposition of carbonate-phosphate complexes, and long-term burial of P. Actively photosynthesizing periphyton can cause super-saturated O2 concentrations near the sediment surface encouraging deposition of metal phosphates. However, anoxia associated with periphyton respiration at night may offset this effect. Linking the small-scale functional role of periphyton to ecosystem-level P retention will require more detailed studies in a variety of ecosystems or large mesocosms. A case study from the Everglades illustrates the importance of considering the role of periphyton in P removal from wetlands. In general, periphyton tends to increase P retention and deposition. In pilot-scale constructed periphyton-dominated wetlands in South Florida, about half of the inflowing total P was removed. 相似文献
100.
Raymond V. Barbehenn 《Entomologia Experimentalis et Applicata》2005,116(3):209-217
Leaf‐chewing insects are commonly believed to be unable to crush the nutrient‐rich bundle sheath cells (BSC) of C4 grasses. This physical constraint on digestion is thought to reduce the nutritional quality of these grasses substantially. However, recent evidence suggests that BSC are digested by grasshoppers. To directly assess the ability of grasshoppers to digest C4 grass BSC, leaf particles of Bouteloua curtipendula (Poaceae) were examined from the digestive tracts of two grasshopper species: Camnula pellucida (Scudder) (primarily a grass feeder) and Melanoplus sanguinipes (Fabricius) (a forb and grass generalist) (Orthoptera: Acrididae). Transmission electron microscopy was used to make the first observations of BSC crushing by herbivorous insects. Camnula pellucida and M. sanguinipes crushed over 58% and 24%, respectively, of the BSC in ingested leaf tissues. In addition, chloroplast and cell membranes were commonly disrupted in uncrushed BSC, permitting soluble nutrients to be extracted, even when BSC walls remain intact. The greater efficiency with which C. pellucida crushes BSC is consistent with the idea that grass‐feeding species are better adapted for handling grass leaf tissues than are generalist species. By demonstrating the effectiveness with which the BSC of B. curtipendula can be crushed and extracted by both species of grasshoppers, this study suggests one reason why C4 grasses are not generally avoided by grasshoppers: at least some C4 grasses can be more easily digested than has been hypothesized. 相似文献