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Tsutomu KAIZU, Yutaka KIRINO, Hiroshi SHIMIZU, A Saturation Transfer Electron Spin Resonance Study on the Break in the Arrhenius Plot for the Rotational Motion of Ca2+ Adenosine Triphosphatase Molecules in Purified and Lipid-Replaced Preparations of Rabbit Skeletal Muscle Sarcoplasmic Reticulum, The Journal of Biochemistry, Volume 88, Issue 6, October 1980, Pages 1837–1843, https://doi.org/10.1093/oxfordjournals.jbchem.a133159
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Abstract
By means of saturation transfer electron spin resonance spectroscopy the rotational motion of spin-labeled Ca2+-dependant ATPase molecules has been investigated for three kinds of preparations of rabbit skeletal muscle sarcoplasmic reticulum: MacLennan′s enzyme (purified ATPase preparation), DOPC-and egg PC-ATPase (purified ATPase preparations in which endogenous lipids are replaced with dioleoyl and egg yolk phosphatidylcholine, respectively). The rotational mobility of the enzyme in these preparations is somewhat lower than that in the intact membrane, probably due to the reduced amount of lipids. For all the preparations, however, the Arrhenius plot for rotational mobility showed a break at about 18°C, the same temperature at which a break in the Arrhenius plot for Ca2+-ATPase activity occurs. This result provides further evidence that the break in the Arrhenius plot is not related to a lipid phase transition but to a change in the physical state of the Ca2+-ATPase molecule existing in fluid lipids.