ACTA, a fluorescent analogue of thapsigargin, is a potent inhibitor and a conformational probe of skeletal muscle Ca²⁺‐ATPase

Abstract

Thapsigargin is a highly potent and selective inhibitor of sarco-endoplasmic reticulum (SERCA) family of Ca P+ -ATPases and a useful tool in research concerning the function of intracellular Ca P+ stores. We describe here a novel fluorescent derivative (8-O-(4-aminocinnamoyl)-8-O-debutanoylthapsigargin, termed ACTA) of this compound, acting as a Ca P+ -ATPase inhibitor with a potency approaching that of thapsigargin. Binding of ACTA to the skeletal muscle sarcoplasmic reticulum vesicles results in a strong fluorescence enhancement, approximately 66% of which depends on ACTA association with Ca P+ -ATPase. This specific component of ACTA fluorescence is sensitive to the E I -E P conformational equilibrium of the pump. The combined properties of high potency and binding-dependent fluorescence suggest ACTA to be a useful probe for a range of studies involving the SERCA class of ATPases.z 1998 Federation of European Biochemical Societies.

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