Separate effects of long-chain phosphatidylcholines on dephosphorylation of the Ca(2+)-ATPase and on Ca2+ binding.
The steady-state activity of the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum (SR) is low when reconstituted into bilayers of the long-chain phosphatidylcholines dierucyl phosphatidylcholine [di(C22:1)PC] or dinervonyl phosphatidylcholine [di(C24:1)PC]. In di(C24:1)PC the ATPase binds a single Ca2+ ion, whereas in di(C22:1)PC it binds two, as in the native SR [Starling, East and Lee (1993) Biochemistry 32, 1593-1600]. In di(C22:1)PC, rates of phosphorylation of the ATPase by ATP and the rate of ATP-induced Ca2+ dissociation are slightly lower than in the native ATPase. However, a much more marked decrease is observed in di(C22:1)PC in the rate of dephosphorylation of the phosphorylated ATPase, which explains the low steady-state ATPase activity. The level of phosphorylation of the ATPase by Pi was little affected by reconstitution in di(C22:1)PC, suggesting that the rate of phosphorylation by Pi is also decreased. The very similar effects of di(C22:1)PC and di(C24:1)PC (Starling, East and Lee (1995) Biochem. J. 310, 875-879) on phosphorylation and dephosphorylation suggest that changes in these steps and the change in Ca2+ binding stoichiometry observed in di(C24:1)PC represent independent changes on the ATPase.
Starling
A P
AP
Department of Biochemistry, University of Southampton, Hants, UK.
East
J M
JM
Lee
A G
AG
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C066558:dinervonylphosphatidylcholine; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium