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  • Geosciences (General)  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Two distinct isoforms of sea urchin egg dynein (1992)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 21 (1992), S. 281-292 
    Details
    ISSN: 0886-1544
    Keywords: ATPase ; CTPase ; minus-end-directed microtubule motility ; cytoplasmic dynein ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Extracts of unfertilized sea urchin eggs contain at least two isoforms of cytoplasmic dynein. One exhibits a weak affinity for microtubules and is primarily soluble. The other isoform, HMr-3, binds to microtubules in an ATP-sensitive manner, but is immunologically distinct from the soluble egg dynein (Porter et al.: Journal of Biological Chemistry 263:6759-6771, 1988). We have now further distinguished these egg dynein isoforms based on differences in NTPase activity. HMr-3 copurifies with NTPase activity, but it hydrolyzes CTP at 10 times the rate of ATP. The soluble egg dynein is similar to flagellar dynein in its nucleotide specificity; its MgCTPase activity is ca. 60% of its MgATPase activity. Non-ionic detergents and salt activate the MgATPase activities of both enzymes relative to their MgCTPase activities, but this effect is more pronounced for the soluble egg dynein than for HMr-3. Sucrose gradient-purified HMr-3 promotes an ATP-sensitive microtubule bundling, as seen with darkfield optics. We have also isolated a 20 S microtubule translocating activity by sucrose gradient fractionation of egg extracts, followed by microtubule affinity and ATP release. This 20 S fraction, which contains the HMr-3 isoform, induces a microtubule gliding activity that is distinct from kinesin. Our observations suggest that soluble dynein resembles axonemal dynein, but that HMr-3 is related to the dynein-like enzymes isolated from a variety of cell types and may represent the cytoplasmic dynein of sea urchin eggs.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970210404
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    Paper (German National Licenses)
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  • 2
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    Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron Tomography (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: We report here the crystal morphologies of MV-1 and ALH84001 magnetites as calculated by back-projection using electron tomography. In the present study, we used a 300 keV TEM with a field emission gun (Tecnai F-30 from FEI Inc.), equipped with a 2048 x 2048 pixel CCD camera from Gatan Inc. to image magnetite crystals over tilt ranges of approx. +/- 72 deg in 2 deg tilt intervals. The images were aligned for back-projection, either manually, or through the use of fiducial 5 nm Au spheres affixed to the specimen prior to microscopy. Three-dimensional (3-D) reconstructions were computed using weighted back-projection of the tilted views. The tomograms were viewed and analyzed as a series of slices 1.0 nm thick, taken parallel to the specimen-supporting grid, using the IMOD software package. The shape of each magnetite crystal was determined by defining the external contour of a given magnetite in each slice and assembling a stack of these contours in 3-D. To aid in visualization, the stacked contour array was reduced to an optimal mesh by Delaunay triangulation. The surface normal to each of the triangles in the mesh was calculated and the triangle faces colored according to the orientation of that surface normal relative to the principal crystallographic axis of magnetite. Green surfaces correspond to {111} orientations, blue surfaces to {100} orientations, and red surfaces to {110} orientations. Triangles whose surface normal did not correspond to one of the principal axes were colored gray. Within the experimental and numerical uncertainties of the deconvolution, the tomographic reconstruction of both MV-1 and ALH84001 magnetites are equivalent and correspond to a truncated hexa-octahedral morphology.
    Keywords: Geosciences (General)
    Type: JSC-CN-7994 , Lunar and Planetary Science XXXIV; LPI-Contrib-1156
    Format: text
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