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181.
Purification, characterization and redox properties of hydrogenase from Methanosarcina barkeri (DSM 800) 总被引:4,自引:0,他引:4
G Fauque M Teixeira I Moura P A Lespinat A V Xavier D V Der Vartanian H D Peck J Le Gall J G Moura 《European journal of biochemistry》1984,142(1):21-28
A soluble hydrogenase from the methanogenic bacterium, Methanosarcina barkeri (DSM 800) has been purified to apparent electrophoretic homogeneity, with an overall 550-fold purification, a 45% yield and a final specific activity of 270 mumol H2 evolved min-1 (mg protein)-1. The hydrogenase has a high molecular mass of approximately equal to 800 kDa and subunits with molecular masses of approximately equal to 60 kDa. The enzyme is stable to heating at 65 degrees C and to exposure to air at 4 degrees C in the oxidized state for periods up to a week. The overall stability of this enzyme is compared with other hydrogenase isolated from strict anaerobic sulfate-reducing bacteria. Ms. barkeri hydrogenase shows an absorption spectrum typical of a non-heme iron protein with maxima at 275 nm, 380 nm and 405 nm. A flavin component, identified as FMN or riboflavin was extracted under acidic conditions and quantified to approximately one flavin molecule per subunit. In addition to this component, 8-10 iron atoms and 0.6-0.8 nickel atom were also detected per subunit. The electron paramagnetic resonance (EPR) spectrum of the native enzyme shows a rhombic signal with g values at 2.24, 2.20 and approximately equal to 2.0. probably due to nickel which is optimally measured at 40 K but still detectable at 77 K. In the reduced state, using dithionite or molecular hydrogen as reductants, at least two types of g = 1.94 EPR signals, due to iron-sulfur centers, could be detected and differentiated on the basis of power and temperature dependence. Center I has g values at 2.04, 1.90 and 1.86, while center II has g values at 2.08, 1.93 and 1.85. When the hydrogenase is reduced by hydrogen or dithionite the rhombic EPR species disappears and is replaced by other EPR-active species with g values at 2.33, 2.23, 2.12, 2.09, 2.04 and 2.00. These complex signals may represent different nickel species and are only observable at temperatures higher than 20 K. In the native preparation, at high temperatures (T greater than 35 K) or in partially reduced samples, a free radical due to the flavin moiety is observed. The EPR spectrum of reduced hydrogenase in 80% Me2SO presents an axial type of spectrum only detectable below 30 K. 相似文献
182.
Soluble cytokeratins in Xenopus laevis oocytes and eggs 总被引:4,自引:0,他引:4
L Gall E Karsenti 《Biology of the cell / under the auspices of the European Cell Biology Organization》1987,61(1-2):33-38
Xenopus oocytes contain a radial network of cytokeratins which seems to fragment during meiosis reinitiation (maturation). The mature egg contains only a cortical network of cytokeratins. We have looked for the presence of soluble cytokeratins in oocytes and unfertilized eggs and have found them in both cases. However, the proportion of soluble to insoluble cytokeratins is slightly higher in the egg than in the oocyte. Soluble cytokeratins incorporate 35S-methionine at a high rate in the oocyte but to a lesser extent in the egg. This suggests that they are biosynthetic intermediates in the oocyte. In the egg, at least a fraction of the soluble cytokeratins may arise from the fragmentation of the polymer which seems to occur during the maturation process. Insoluble cytokeratins are strongly labeled with 32P both in oocytes and eggs. On the other hand only the soluble keratins of the egg incorporate 32P. Since the isoelectric point of soluble and insoluble cytokeratins is the same in oocytes and eggs, their absolute level of phosphorylation probably remains relatively constant. This suggests that: i) phosphate turnover is very slow in oocyte soluble cytokeratins, ii) phosphorylation is not a major way of changing the structural state of cytokeratins in amphibian oocytes and eggs. 相似文献
183.
Authors report one family with three cases of myeloblastic acute leukaemia in three generations. In this family, without chromosomal abnormalities (the only one possible laboratory examination), the risk is certainly increased, but it remains, fortunately, low. 相似文献
184.
185.
Lars Gall Razvan C. Stan Alice Kress Brigitte Hertel Gerhard Thiel Tobias Meckel 《Traffic (Copenhagen, Denmark)》2010,11(4):548-559
Using the bright, photostable, charged and hydrophilic fluorescent dye Alexa 488 hydrazide to label the fluid phase around intact guard cells, we show that these cells incorporate the fluid phase during constitutive endocytosis against the high turgor. Mobile, cortical and diffraction‐limited signals were not observed if a concentration <4 mm was used to stain the fluid phase, suggesting that endocytic vesicles had to be loaded with a minimal number of dye molecules to produce a signal above the background. To quantify the number of molecules taken up by the vesicles, we prepared liposomes, filled with various concentrations of Alexa 488 hydrazide, fractionated them according to their size and imaged them under identical conditions as the guard cells. From the size/intensity relations of these liposomes, we extrapolated the molecular brightness of Alexa 488 hydrazide. Using this calibration, the mean fluorescent intensity of single endocytic vesicles translates into a mean number of 573 Alexa 488 molecules. If a vesicle needs to take up 573 molecules from a 4 mm solution, it requires a diameter of at least 87 nm. This number provides the first in vivo estimate for the size of endocytic vesicles in intact, turgid plant cells. 相似文献
186.
187.
Christopher M. Yakacki Mariya Poukalova Robert E. Guldberg Angela Lin Minn Saing Scott Gillogly Ken Gall 《Journal of biomechanics》2010,43(10):1953-1959
This study investigates how the microstructural properties of trabecular bone affect suture anchor performance. Seven fresh-frozen humeri were tested for pullout strength with a 5 mm Arthrex Corkscrew in the greater tuberosity, lesser tuberosity, and humeral head. Micro-computed tomography analysis was performed in the three regions of interest directly adjacent to individual pullout experiments. The morphometric properties of bone mineral density (BMD), structural model index (SMI), trabecular thickness (TbTh), trabecular spacing (TbS), trabecular number (TbN), and connectivity density were compared against suture anchor pullout strength. BMD (r=0.64), SMI (r=?0.81), and TbTh (r=0.71) showed linear correlations to the pullout strength of the suture anchor with p-values<0.0001. A predictive model was developed to explain the variances in the individual BMD, SMI, and TbTh correlations. The multi-variant model of pullout strength showed a stronger relationship (r=0.86) compared to the individual experimental results. This study helps confirm BMD is a major influence on the pullout strength of suture anchors, but also illustrates the importance of local microstructure in pullout resistance of suture anchors. 相似文献
188.
189.
Fb, a ndw enzymatic fragment of human G immunoglobulin 总被引:4,自引:0,他引:4
190.
D.Grant Gall Daniel G. Butler Fern Tepperman J.Richard Hamilton 《生物化学与生物物理学报:生物膜》1974,339(3):291-302
A technique to measure Na+ efflux from isolated intestinal epithelial cells has permitted us to examine the mechanisms responsible for Na+ transport in absorptive cells without contamination by other cell types. We examined the effect of actively transported sugars on Na+ efflux from isolated rat jejunal epithelial cells to evaluate the mechanism by which actively transported non-electrolytes stimulate Na+ absorption. Glucose, galactose and 3-O-methylglucose, sugars known to be actively transported by the small intestine, stimulate total Na+ efflux from isolated epithelial cells. This stimulation results from an increase of active Na+ transport, since it is inhibited by ouabain. Glucose stimulation is significantly greater than that produced by galactose or 3-O-methylglucose, 2-Deoxyglucose, a sugar that is not actively transported, has no effect on total Na+ efflux from isolated cells. Phloridzin, which has no effect on Na+ efflux in a sugar-free medium, completely abolishes the effect of galactose. These findings (a) support the hypothesis that the increase in intestinal absorption of Na+ in the presence of actively transported non-electrolytes occurs by a transcellular route; and (b) are consistent with the ion-gradient model. The results are not compatible with the direct energy-coupling model. 相似文献