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1981 (1)
1Author    Peter Laggner, Josef Suko, Christian Punzengruber, Rudolf PragerRequires cookie*
 Title    Electron Spin Resonance Studies on Conformational Changes of the Sarcoplasmic Reticulum Ca 2+ -ATPase Induced by Synergistic Action of Calcium and ATP  
 Abstract    Changes in motional properties of the -SH group environment in sarcoplasmic reticulum ATPase [1] induced by addition of specific ligands to sarcoplasmic reticulum membrane vesicles were investigated systematically by electron spin resonance (e.p.r.) spectro-scopy. Alternatively, two kinds of iodoacetamide analog spin labels, 4-(2-iodoacetamido)-2,2,5,5-tetramethyl-l-pyrrolidinyl-N-oxyl (label I) and 4-(2-iodoacetamido)-2,2,6,6-tetra-methyl-l-piperidinyl-N-oxyl (label II) were used. The labeling conditions were chosen such that less than three moles of -SH groups per mole of ATPase reacted with the spin labels. A marked increase in isotropic motion of either spin label was observed on addition of calcium in millimolar concentrations plus ATP or /S-y-methylene ATP. Qualitatively similar but smaller changes were also observed with inosine 5'-triphosphate (ITP), acetylphosphate, or ADP in the presence of calcium. These effects were independent of added magnesium. The spectral changes induced by ß-y-methylene ATP, which binds to the ATPase but is not hydrolyzed, and those of calcium plus ADP suggest a conformational change due to simultaneous binding of these ligands in the absence of enzyme phosphoryla-tion. These changes in e.p.r. spectra were different in quality and magnitude from those observed upon separate binding of calcium or adenine nucleotides. The two spin labels, differing only in their numbers of heterocyclic ring atoms, were found to reflect environmental changes in different ways. This demonstrates the usefulness of employing different spin labels to detect and interpret structural transitions in macro-molecular assemblies. The active transport of calcium by sarcoplasmic reticulum membranes isolated from skeletal muscle is generally considered to be a multistep process [1, 2], Several models for the reaction sequence of calcium translocation by the calcium pump of sarcoplasmic reticulum have been proposed on the basis of kinetic experiments [2-11]. In order to detect and characterize structural alterations of the ATPase in the calcium transport cycle, e.p.r. spectroscopic investigations of spin-labeled sarco-plasmic reticulum preparations, first introduced by 
  Reference    Z. Naturforsch. 36b, 1136—1143 (1981); received February 2 1981 
  Published    1981 
  Keywords    Sarcoplasmic Reticulum, Spin Labeling, Calcium-ATPase 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-1136.pdf 
 Identifier    ZNB-1981-36b-1136 
 Volume    36