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991.
Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants, fungi, and animals, at least seven complex I subunits (ND1, -2, -3, -4, -4L, -5, and -6; ND is NADH dehydrogenase) are coded by mitochondrial genes. The role of these highly hydrophobic subunits in the enzyme activity and assembly is still poorly understood. In the unicellular green alga Chlamydomonas reinhardtii, the ND3 and ND4L subunits are encoded in the nuclear genome, and we show here that the corresponding genes, called NUO3 and NUO11, respectively, display features that facilitate their expression and allow the proper import of the corresponding proteins into mitochondria. In particular, both polypeptides show lower hydrophobicity compared to their mitochondrion-encoded counterparts. The expression of the NUO3 and NUO11 genes has been suppressed by RNA interference. We demonstrate that the absence of ND3 or ND4L polypeptides prevents the assembly of the 950-kDa whole complex I and suppresses the enzyme activity. The putative role of hydrophobic ND subunits is discussed in relation to the structure of the complex I enzyme. A model for the assembly pathway of the Chlamydomonas enzyme is proposed. 相似文献
992.
Joyeux-Faure M Rossini E Ribuot C Faure P 《Experimental biology and medicine (Maywood, N.J.)》2006,231(4):456-462
High fructose-fed (HFF) rat model is known to develop the insulin-resistant syndrome with a very similar metabolic profile to the human X syndrome. Such metabolic modifications have been associated with a high incidence of cardiovascular disease. The role of free radical attack in diabetes mellitus and its cardiovascular complications have been abundantly documented. The present study examined the susceptibility to myocardial ischemic injury and the involvement of free radical attack and/or protection in the metabolic disorders of high FF rats. Rats were divided into two experimental groups that received diet for 4 weeks: a control group (C, n=28) receiving a standard diet and a HFF group (FF, n=28), in which 58% of the total carbohydrate was fructose. The euglycemic clamp technique was performed to assess insulin resistance. For the ischemia-reperfusion procedure, rat hearts were isolated and perfused at constant pressure before they were subjected to a 30-min occlusion of the left coronary artery followed by 120 mins of reperfusion. Hemodynamic parameters were measured throughout the protocol. Infarct-to-risk ratio (I/R) was assessed at the end of the protocol by 2,3,4-triphenyltetrazolium chloride staining and planimetric analysis. Lipid peroxidation, antioxidant enzyme activity, level of vitamin E, and trace element status were measured in blood samples from both groups. Rats of the FF group developed an insulin resistance indicated by the glucose infusion rate, which was decreased by 47%. Infarct size was significantly reduced in rats from the FF group (19.9% +/- 6.6%) compared to rats from the control group (34.6% +/- 4.9%), and cardiac functional recovery at reperfusion was improved in the FF group. Lipid peroxidation and oxidative stress were higher in the FF group, as indicated by higher malonedialdehyde level, whereas plasma vitamin E/triacylglycerol ratio was also enhanced in this group. This study indicates that fructose feeding affords protection against in vitro ischemia-reperfusion injury, potentially implicating vitamin E. 相似文献
993.
The survival and colonisation potential of photoautotrophic microbes (cyanobacteria and microalgae) were investigated in three
terrestrial environments within a glacierised catchment on Svalbard: old vegetation-covered soil, recently deglaciated barren
soil and subglacial sediments. One-year reciprocal transplant incubations of photoautotrophic microbial communities from the
three soil/sediment environments were conducted in order to reveal the autochthonous or allochthonous origin of the present
photoautotrophs. The abundance and taxonomic composition of photoautotrophic microbes and their changes over time and between
soil/sediment types and physico-chemical characteristics of the soils/sediments were determined. The recovery time of a photoautotrophic
community by import of cells was between several months in subglacial and vegetated soils and up to 27 years in proglacial
soils. No active growth was recorded in subglacial sediments, whilst positive growth, and so the potential for autochthonous
recovery, was found in proglacial and vegetated soils. The most suitable environment for the survival of transplanted microbes
was provided in proglacial soil. We show here that the new proglacial substrata can be successfully colonised by photoautotrophic
microbes, and that input of allochthonous cells may, in some cases, exceed in situ microbial growth. Whilst the subglacial
environment is rather a conduit for photoautotrophic microbes than a place of growth and production, the supply of viable
photoautotrophs in it is relatively high and may serve as a significant resource of nutrients for subglacial microbial communities. 相似文献
994.
Sébastien Moreau Gustavo A. Ferreyra Bernard Mercier Karine Lemarchand Marie Lionard Suzanne Roy Behzad Mostajir Sébastien Roy Bon van Hardenberg Serge Demers 《Polar Biology》2010,33(12):1599-1614
Although winter conditions play a major role in determining the productivity of the western Antarctic Peninsula (WAP) waters for the following spring and summer, a few studies have dealt with the seasonal variability of microorganisms in the WAP in winter. Moreover, because of regional warming, sea-ice retreat is happening earlier in spring, at the onset of the production season. In this context, this study describes the dynamics of the marine microbial community in the Melchior Archipelago (WAP) from fall to spring 2006. Samples were collected monthly to biweekly at four depths from the surface to the aphotic layer. The abundance and carbon content of bacteria, phytoplankton and microzooplankton were analyzed using flow cytometry and inverted microscopy, and bacterial richness was examined by PCR–DGGE. As expected, due to the extreme environmental conditions, the microbial community abundance and biomass were low in fall and winter. Bacterial abundance ranged from 1.2 to 2.8 × 105 cells ml?1 showing a slight increase in spring. Phytoplankton biomass was low and dominated by small cells (<2 μm) in fall and winter (average chlorophyll a concentration, Chl-a, of, respectively, 0.3 and 0.13 μg l?1). Phytoplankton biomass increased in spring (Chl-a up to 1.13 μg l?1), and, despite potentially adequate growth conditions, this rise was small and phytoplankton was still dominated by small cells (2–20 μm). In addition, the early disappearing of sea-ice in spring 2006 let the surface water exposed to ultraviolet B radiations (UVBR, 280–320 nm), which seemed to have a negative impact on the microbial community in surface waters. 相似文献
995.
996.
997.
Molecular markers belonging to the three different genomes, mitochondrial (cox2‐cox3 spacer), plastid (rbcL), and nuclear (internal transcribed spacer [ITS] 2 region), were used to compare samples of the two morphologically related species Gracilaria gracilis (Stackh.) Steentoft, L. M. Irvine et Farnham and G. dura (C. Agardh) J. Agardh collected along Atlantic coasts. In northern Europe, the distinction between these two species is ambiguous, and they are currently recognized under the single name of G. gracilis. The low but congruent patterns of genetic divergence observed for markers of the three genomic compartments highly suggest that these two taxa correspond effectively to two different genetic entities as previously described 200 years ago, based on morphological traits. However, thanks to the combination of different DNA markers, occurrence of “incongruent” cytotypes (i.e., mitotypes of G. dura associated with chlorotypes of G. gracilis) in individuals collected from Brittany, suggests interspecific hybridization between the two sibling species studied. 相似文献
998.
Hua-Poo Su Youwei Yan G. Sridhar Prasad Robert F. Smith Christopher L. Daniels Pravien D. Abeywickrema John C. Reid H. Marie Loughran Maria Kornienko Sujata Sharma Jay A. Grobler Bei Xu Vinod Sardana Timothy J. Allison Peter D. Williams Paul L. Darke Daria J. Hazuda Sanjeev Munshi 《Journal of virology》2010,84(15):7625-7633
999.
Marie Deghorain Laetitia Fontaine Blandine David Jean-Luc Mainardi Pascal Courtin Richard Daniel Jeff Errington Alexei Sorokin Alexander Bolotin Marie-Pierre Chapot-Chartier Bernard Hallet Pascal Hols 《The Journal of biological chemistry》2010,285(31):24003-24013
Cell wall peptidoglycan assembly is a tightly regulated process requiring the combined action of multienzyme complexes. In this study we provide direct evidence showing that substrate transformations occurring at the different stages of this process play a crucial role in the spatial and temporal coordination of the cell wall synthesis machinery. Peptidoglycan substrate alteration was investigated in the Gram-positive bacterium Lactococcus lactis by substituting the peptidoglycan precursor biosynthesis genes of this bacterium for those of the vancomycin-resistant bacterium Lactobacillus plantarum. A set of L. lactis mutant strains in which the normal d-Ala-ended precursors were partially or totally replaced by d-Lac-ended precursors was generated. Incorporation of the altered precursor into the cell wall induced morphological changes arising from a defect in cell elongation and cell separation. Structural analysis of the muropeptides confirmed that the activity of multiple enzymes involved in peptidoglycan synthesis was altered. Optimization of this altered pathway was necessary to increase the level of vancomycin resistance conferred by the utilization of d-Lac-ended peptidoglycan precursors in the mutant strains. The implications of these findings on the control of bacterial cell morphogenesis and the mechanisms of vancomycin resistance are discussed. 相似文献
1000.
Celestine N. Chi Anders Bach Marie Gottschalk Anders S. Kristensen Kristian Str?mgaard Per Jemth 《The Journal of biological chemistry》2010,285(36):28252-28260
Dimeric ligands can be potent inhibitors of protein-protein or enzyme-substrate interactions. They have increased affinity and specificity toward their targets due to their ability to bind two binding sites simultaneously and are therefore attractive in drug design. However, few studies have addressed the kinetic mechanism of interaction of such bivalent ligands. We have investigated the binding interaction of a recently identified potent plasma-stable dimeric pentapeptide and PDZ1–2 of postsynaptic density protein-95 (PSD-95) using protein engineering in combination with fluorescence polarization, isothermal titration calorimetry, and stopped-flow fluorimetry. We demonstrate that binding occurs via a two-step process, where an initial binding to either one of the two PDZ domains is followed by an intramolecular step, which produces the bidentate complex. We have determined all rate constants involved in the binding reaction and found evidence for a conformational transition of the complex. Our data demonstrate the importance of a slow dissociation for a successful dimeric ligand but also highlight the possibility of optimizing the intramolecular association rate. The results may therefore aid the design of dimeric inhibitors in general. 相似文献