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Abstract:
Lipid deprivation of the sarcoplasmic reticulum calcium‐transport ATPase neither affects the enzyme's affinity for ATP nor that of calcium. 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 calcium‐dependent ATP hydrolysis restores vanadate binding. Concomitantly the mutual interactions between vanadate and calcium 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 calcium follow the same time course. Conversely, the displacement of vanadate by calcium 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 calcium binding sites.
