Lipid requirement of the vanadate effect on the binding of calcium and ATP to the calcium transport ATPase of the sarcoplasmic reticulum

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Abstract
Lipid deprivation of the [rabbit muscle] sarcoplasmic reticulum Ca-transport ATPase neither affects the enzyme''s affinity for ATP nor that of Ca. In contrast. Vanadate binding is almost completely abolished. Lipid substitution by oleic acid which at a ratio of 0.3 mg/mg protein completely reactivates the Ca-dependent ATP hydrolysis restores vanadate binding. Concomitantly the mutual interactions between vanadate and Ca or ATP and ADP, respectively, are restored. The vanadate-induced disappearance of the enzyme''s ATP binding sites as well as its high-affinity binding sites for Ca follow the same time course. Conversely, the displacement of vanadate by Ca proceeds in parallel with the recovery of ADP binding. In lipid-restituted preparations as well as in native membranes vanadate induces the disappearance of external high-affinity and simultaneously the appearance of internal low-affinity Ca binding sites.