Effects of phospholipids on binding of calcium to (Ca2(+)-Mg2(+)-ATPase.

The (Ca2(+)-Mg2(+)-ATPase purified from skeletal muscle sarcoplasmic reticulum binds two Ca2+ ions per ATPase molecule. On reconstitution into bilayers of dioleoylphosphatidylcholine [C18:1)PC) or dinervonylphosphatidylcholine [C24:1)PC) the stoichiometry of binding remains unchanged, but when the ATPase is reconstituted into bilayers of dimyristoleoylphosphatidylcholine [C14:1)PC) the stoichiometry changes to one Ca2+ ion per ATPase molecule. Nevertheless, the level of phosphorylation is the same for the ATPase reconstituted with (C18:1)PC or (C14:1)PC. The effect of (C14:1)PC on the stoichiometry of Ca2+ binding is prevented by androstenol at a 1:1 molar ratio with the phospholipid.