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  • 1
    Electronic Resource
    Electronic Resource
    Calcium binding and fluorescence measurements of dansylaziridine-labelled troponin C in reconstituted thin filaments (1987)
    Springer
    Journal of muscle research and cell motility 8 (1987), S. 428-436 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The direct binding of Ca2+ to reconstituted thin filaments containing troponin C and the 5-dimethylaminonaphthalene-1-sulphonylaziridine (DANZ) fluorescent analogue of troponin C (TnC DANZ ) was measured (25° C) at three Mg2+ concentrations. Biphasic Scatchard plots were found for all binding curves reflecting the binding of Ca2+ to high- and low-affinity sites of troponin. The binding of Ca2+ to the high-affinity sites had a greater sensitivity to Mg2+ (K Mg=1×104 m −1) than the low-affinity sites (K Mg=1.2×103 m −1). The fluorescence change of thin filaments reconstituted with TnC DANZ was titrated with Ca2+ in the same solutions used for binding assays. The Ca2+-dependent fluorescence change had nearly the same sensitivity to Mg2+ (K Mg=9.4×102 m −1) as did Ca2+ binding to the low-affinity sites. The Ca2+ concentration at the midpoint of the fluorescence change was about 0.3 log units less than at the midpoint for Ca2+ binding to the low-affinity sites. A similar relationship between the fluorescence change and Ca2+ binding to the low-affinity sites of isolated TnC DANZ was measured (4° C). From these results the binding of Ca2+ to either low-affinity site is concluded to produce the fluorescence change. In comparison with the low-affinity sites of isolated troponin and troponin-tropomyosin complex, the low-affinity sites of reconstituted thin filaments were consistently lower in Ca2+ affinity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01578432
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  • 2
    Electronic Resource
    Electronic Resource
    Functional implications of the unusual amino acid sequence of the regulatory light chain ofAcanthamoeba castellanii myosin-II (1991)
    Springer
    Journal of muscle research and cell motility 12 (1991), S. 553-559 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have determined by protein chemistry methods the amino acid sequence of light chain 2 fromAcanthamoeba castellanii myosin-II (ALC2). This is the first reported sequence for any protozoan myosin light chain. ALC2 consists of 154 amino acid residues, including a single residue of His and two residues each of Pro and Tyr, and lacks Cys and Trp. The N-terminus is blocked, and if an N-terminal acetyl group is assumed, ALC2 has a calculated molecular weight of 17657. ALC2 is an acidic protein, with a calculated net charge of — 7 at pH 7. The sequence of ALC2 is most similar to those of the calmodulins (identity approximately 35%, followed by myosin regulatory light chains. ALC2 appears to lack the potential N-terminal phosphorylation site and single Ca2+-binding site in region I which are characteristic of most myosin regulatory light chains. Instead, ALC2, unlike any other myosin light chain characterized to date, may have a functional Ca2+-binding site only in region II, suggesting a novel role of ALC2 in the Ca2+ regulation of the activity ofAcanthamoeba myosin-II.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01738443
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  • 3
    Electronic Resource
    Electronic Resource
    Phospholipid membrane-associated brush border myosin-I activity (1995)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 30 (1995), S. 26-37 
    Details
    ISSN: 0886-1544
    Keywords: myosin ; myosin-I ; unconventional myosin ; brush border ; epithelia ; membrane ; phospholipid ; fluorescence microscopy ; actin ; calmodulin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Brush border myosin-I (BBMI) is associated with the membrane of intestinal epithelial cells where it probably plays a structural role. BBMI also has been identified on Golgi-derived vesicles in intestinal epithelial cells where it may translocate vesicles into the brush border. However, the mechanochemical activity of BBMI bound to a phospholipid membrane has not been described. This study reports that phospholipid membrane-associated BBMI displays ATPase activity when bound to phospholipids, but does not move actin filaments when associated with a phospholipid bilayer. BBMI does not bind significantly to brush border membrane lipids, which contain about 16% phosphatidylserine (PS), in either a pelleting or planar membrane assay. Similarly, planar membranes containing 20% PS do not bind a significant amount of BBMI. Increasing the concentration of PS to 40% does result in the binding of BBMI to both vesicles and planar membranes. This binding is enhanced with increased Ca2+ concentrations. BBMI retains its ATPase activity when bound to phospholipid vesicles containing 40% PS. However, BBMI attached to a phospholipid bilayer surface does not move actin filaments, even though the amount of BBMI bound to the lipid surface, as reflected by the number of actin filaments associated with bilayer-bound BBMI, is sufficient to observe motility in control experiments. When membrane fluidity is reduced by adding cholesterol to the membrane lipids containing 40% PS, BBMI still binds to the membrane, but again no actin filament motility is observed. The lack of binding by BBMI to brush border membrane lipids and the absence of membrane-associated BBMI mechanical activity suggest that factors in addition to membrane lipids are necessary for membrane-associated myosin-I motility. © 1995 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970300105
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