EFFECTS OF PHOSPHOLIPID FATTY ACYL-CHAIN LENGTH ON PHOSPHORYLATION AND DEPHOSPHORYLATION OF THE CA2-ATPASE()

The kinetics of the Ca2+-ATPase purified from sarcoplasmic reticulum h ave been studied after reconstitution into bilayers of dimyristoleoylp hosphatidylcholine [di(C-14:1)PC], dioleoylphosphatidylcholine [di(C-1 8:1)PC] and dinervonylphosphatidylcholine [di(C-24:1)PC]. In di(C-24:1 )PC the rate of phosphorylation of the ATPase by ATP was comparable wi th that in di(C-18:1)PC (about 70 s(-1)), but in di(C-14:1)PC the rate was much lower (21 s(-1)). Fluorescence responses of the ATPase sugge st changes in the phosphoryl-transfer step rather than in the precedin g conformational change E1Ca(2)ATPT reversible arrow E1'Ca(2)ATP. The rate of dephosphorylation of the phosphorylated ATPase was found to de crease in the order di(C-24:1)PC < di(C-14:1)PC < di(C-18:1)PC. For th e ATPase in di(C-24:1)PC the rate of dephosphorylation (3.3 s(-1)) was slow enough to be the rate-limiting step for ATP hydrolysis; in di(C- 14:1)PC, it is suggested that both phosphorylation and dephosphorylati on contribute to rate limitation. Phosphorylation of the ATPase in di( C-24:1)PC by P-i was normal, but no phosphoenzyme could be detected in di(C-14:1)PC. The rate of the Ca2+-transport step was normal in di(C- 24:1)PC, suggesting that the single Ca2+ ion bound to the ATPase in di (C-24:1)PC could be transported.