Accumulation of Ca2+ by the Ca2+-ATPase of skeletal-muscle sarcoplasmic reticulum has been measured in reconstituted, sealed vesicles as a function of lipid composition. Measurements were performed in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) to eliminate any effects of H+ transport; in the presence of FCCP, addition of valinomycin had no effect on the level or rate of accumulation of Ca2+ showing that, in the presence of FCCP, no electrical potential built up across the membrane. Levels of accumulation were low when the phospholipid was dioleoylphosphatidylcholine (DOPC), even though DOPC supports high ATPase activity. Inclusion of 10 mol% anionic phospholipid [dioleoylphosphatidic acid (DOPA) or dioleoylphosphatidylserine (DOPS)] led to higher levels of accumulation of Ca2+, 10 mol% being the optimum concentration. Cardiolipin or phosphatidylinositol 4-phosphate were more effective than DOPA or DOPS in increasing accumulation of Ca2+. Effects of anionic phospholipids were seen in the presence of an ATP-regenerating system to remove ADP, and in the presence of phosphate within the reconstituted vesicles to precipitate calcium phosphate. Rates of passive leak of Ca2+ from the reconstituted vesicles were slow. The Ca2+-accumulation process was simulated assuming either simple passive leak of Ca2+ from the vesicles or assuming slippage on the ATPase, a process in which the phosphorylated intermediate of the ATPase releases bound Ca2+ on the cytoplasmic rather than the lumenal side of the membrane. The experimental data fitted to a slippage model, with anionic phospholipids decreasing the rate of slippage.
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Research Article|
August 24 1999
Anionic phospholipids decrease the rate of slippage on the Ca2+-ATPase of sarcoplasmic reticulum
Kate A. DALTON;
Kate A. DALTON
1Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, U.K.
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Jeffrey D. PILOT;
Jeffrey D. PILOT
1Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, U.K.
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Sanjay MALL;
Sanjay MALL
1Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, U.K.
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J. Malcolm EAST;
J. Malcolm EAST
1Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, U.K.
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Anthony G. LEE
Anthony G. LEE
1
1Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, U.K.
1To whom correspondence should be addressed (agl.soton.ac.uk).
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Publisher: Portland Press Ltd
Received:
April 13 1999
Revision Received:
May 26 1999
Accepted:
June 25 1999
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1999
1999
Biochem J (1999) 342 (2): 431–438.
Article history
Received:
April 13 1999
Revision Received:
May 26 1999
Accepted:
June 25 1999
Citation
Kate A. DALTON, Jeffrey D. PILOT, Sanjay MALL, J. Malcolm EAST, Anthony G. LEE; Anionic phospholipids decrease the rate of slippage on the Ca2+-ATPase of sarcoplasmic reticulum. Biochem J 1 September 1999; 342 (2): 431–438. doi: https://doi.org/10.1042/bj3420431
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