Effects of phospholipid fatty acyl chain length on phosphorylation and dephosphorylation of the Ca(2+)-ATPase.
The kinetics of the Ca(2+)-ATPase purified from sarcoplasmic reticulum have been studied after reconstitution into bilayers of dimyristoleoylphosphatidylcholine [di(C14:1)PC], dioleoylphosphatidylcholine[di(C18:1)PC] and dinervonylphosphatidylcholine [di(C24:1)PC]. In di(C24:1)PC the rate of phosphorylation of the ATPase by ATP was comparable with that in di(C18:1)PC (about 70 s-1), but in di(C14:1)PC the rate was much lower (21 s-1). Fluorescence responses of the ATPase suggest changes in the phosphoryl-transfer step rather than in the preceding conformational change E1Ca2ATP<-->E1'Ca2ATP. The rate of dephosphorylation of the phosphorylated ATPase was found to decrease in the order di(C24:1)PC < di(C14:1)PC < di(C18:1)PC. For the ATPase in di(C24:1)PC the rate of dephosphorylation (3.3 s-1) was slow enough to be the rate-limiting step for ATP hydrolysis; in di(C14:1)PC, it is suggested that both phosphorylation and dephosphorylation contribute to rate limitation. Phosphorylation of the ATPase in di(C24:1)PC by Pi was normal, but no phosphoenzyme could be detected in di(C14:1)PC. The rate of the Ca(2+)-transport step was normal in di(C24:1)PC, suggesting that the single Ca2+ ion bound to the ATPase in di(C24:1)PC could be transported.
Starling
A P
AP
Department of Biochemistry, University of Southampton, Hants, U.K.
East
J M
JM
Lee
A G
AG
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification / Q000378:metabolism*; D005227:Fatty Acids; D007700:Kinetics; D008051:Lipid Bilayers; D008274:Magnesium / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000201:enzymology; D010713:Phosphatidylcholines; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D013329:Structure-Activity Relationship
D005227:Fatty Acids; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D000252:Calcium-Transporting ATPases; D008274:Magnesium