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1989 (1)
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1Author    S. P. Marfey, R. Van Meter, M. E. BartletRequires cookie*
 Title    Interaction between Cholesterol and Calcium Ions in Solution  
 Abstract    Dialysis rates of cholesterol, calcium chloride dihydrate and of their mixture in 90% aqueous dioxane through Visking cellulose membrane were characterized by half-escape times (U/t) of 2.2, 1.0 and 10.5 hours, respectively. Slow dialysis rate observed with the mixture was due to complex formation between four molecules of cholesterol and two molecules of calcium chloride dihydrate, molecular weight 1800 to 2000. The association constant for this complex in 90% aqueous dioxane was estimated to be 3.9 x 1014. Rates of dialysis obtained with a natural protein membrane were in the reverse order to those obtained with cellulose membrane. Half-escape times for cholesterol, calcium chloride dihydrate and for their mixture were 0.6, 6.7 and 1.4 hours, respectively. Deter­ minations of milliosmolality of the three solutions by freezing point depression indicated that in the mixture there were fewer osmotically active same molarity, also suggesting formation of the ments. 
  Reference    (Z. Naturforsch. 30c, 718 [1975]; received June 3 1975) 
  Published    1975 
  Keywords    Cholesterol-Calcium Complex, Calcium Binding, Cholesterol Binding, Arteriosclerosis 
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 TEI-XML for    default:Reihe_C/30/ZNC-1975-30c-0718.pdf 
 Identifier    ZNC-1975-30c-0718 
 Volume    30 
2Author    Wilhelm Hasselbach, Vera KoenigRequires cookie*
 Title    Low Affinity Calcium Binding Sites of the Calcium Transport ATPase of Sarcoplasmic Reticulum Membranes  
 Abstract    Calcium binding sites having low affinity constants of < 103 M-1 were titrated in native sarcoplasmic reticulum vesicles as well as in lipid deprived m em branes and in the isolated calcium transport ATPase. Short time calcium binding m easurem ents and the determ ination o f the calcium binding heat allow to distinguish low affinity calcium binding sites located on the external surface of the sarcoplasmic reticulum m em branes from those present in the section o f the transport molecule directed to the vesicular space. The same num ber o f internal binding sites was found for preparations deprived of their lipid content as well as of preparations depleted o f their lipids and of their accessorial proteins. Magnesium interferes with calcium binding to the external as well as to the internal low affinity calcium binding sites. The im plications o f the existence o f the low affinity calcium binding sites in the internal section o f the calcium transport ATPase are discussed. 
  Reference    Z. Naturforsch. 35c, 1012 (1980); received A ugust 27 1980 
  Published    1980 
  Keywords    Sarcoplasmic Reticulum, Calcium Binding, Low Affinity Binding Sites 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-1012.pdf 
 Identifier    ZNC-1980-35c-1012 
 Volume    35 
3Author    Elisabeth Fassold, Wilhelm Hasselbach, Bernd KüchlerRequires cookie*
 Title    Effect of Non-Solubilizing SDS Concentrations on High Affinity Ca2+ Binding and Steady State Phosphorylation by Inorganic Phosphate of the Sarcoplasmic Reticulum ATPase  
 Abstract    In this investigation low, non-solubilizing concentrations of the strong anionic detergent SDS were used to perturbate the interaction of Ca2+ and P, with their respective binding domains on the sarcoplasmic reticulum Ca-transport ATPase. Rising SDS concentrations produce a two-step decline of Ca2+-dependent ATP hydrolysis. At pH 6.15, SDS differently affects high affinity Ca2+ binding and phosphorylation by inorganic phosphate and releases the "mutual exclusion" of these two ligand binding steps. The degree of uncoupling is considerably more pronounced in the presence of 20% Me2SO. The reduction of Ca2+ binding by SDS is demonstrated to be a result of decreased affinity of one of the two specific high affinity binding sites and of perturbation of their cooperative inter­ action. Higher SDS partially restores the original high Ca2f affinity but not the cooperativity of binding. Phosphorylation exhibits a higher SDS sensitivity than Ca2+ binding: Increasing SDS competitively inhibits and then completely abolishes phosphoenzyme formation. Thus. SDS binds to the phosphorylation domain, evidently involving the Lys352 residue of the ATPase molecule; this is accompanied by a more unspecific concentration-dependent SDS effect, probably mediated by hydrophobic force, which, finally, suppresses phosphorylation. Me2SO does neither qualitatively affect the SDS-dependent chemical properties of the vesicular material nor the SDS-dependent perturbation of the investigated reaction steps. 
  Reference    Z. Naturforsch. 44c, 139 (1989); received November 28 1988 
  Published    1989 
  Keywords    Sarcoplasmic Reticulum ATPase, Calcium Binding, Phosphorylation, SDS 
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 TEI-XML for    default:Reihe_C/44/ZNC-1989-44c-0139.pdf 
 Identifier    ZNC-1989-44c-0139 
 Volume    44