Transmembrane Ca2+ gradient-mediated phosphatidylcholine modulating sarcoplasmic reticulum C(a2+)-ATPase.
The sarcoplasmic reticulum (SR) C(a2+)-ATPase was purified and reconstituted into the sealed phospholipids vesicles with or without transmembrane Ca2+ gradient. The role of phospholipids, especially phosphatidylcholine (PC), in the modulation of C(a2+)-ATPase by transmembrane Ca2+ gradient was investigated. The results are as follows. (i) Incubated with phospholipids, the enzyme activity of the delipidated C(a2+)-ATPase is inhibited by Ca2+ and the highest inhibition is observed in the presence of PC. (ii) When there exists a transmembrane Ca2+ gradient (higher Ca2+ concentration inside vesicles, 1,000 mumol/L:50 mumol/L, similar to the physiological condition), the inhibition of C(a2+)-ATPase by transmembrane Ca2+ gradient can be only observed in the vesicles containing PC:PE, but not in those containing PS:PE or PG:PE. The highest inhibition is obtained at a 50:50 molar ratio of PC:PE (iii) By comparing the effects of PC differing in acyl chains, higher inhibition of C(a2+)-ATPase is observed in vesicles containing DPPC:PE and DOPC:PE, while no inhibition in DMPC:PE vesicles (iv) If the transmembrane Ca2+ gradient is in the inverse direction, the enzyme activity of C(a2+)-ATPase is inhibited whenever reconstituted with acidic or neutral phospholipids.
Tu
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State Key Laboratory of Biomacromolecules, Chinese Academy of Sciences,Beijing.
Xu
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Yang
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D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D008564:Membrane Potentials; D010713:Phosphatidylcholines / Q000494:pharmacology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D010713:Phosphatidylcholines; D000252:Calcium-Transporting ATPases; D002118:Calcium