Arsenate-induced fluorescence changes in the Ca 2+-ATPase of sarcoplasmic reticulum membranes

Abstract

Arsenate, an analogue of inorganic phosphate, causes an increase in the intrinsic fluorescence of the Ca 2+-ATPase of sarcoplasmic reticulum membranes. This increase in fluorescence is observed regardless of whether Ca 2+-loaded or leaky vesicles are assayed. The maximal fluorescence change (2–3%) is observed at pH 6.0 in the presence of Mg 2+ and is abolished by the addition of micromolar Ca 2+ concentrations. Dimethyl sulfoxide (20% v v ) increases the enzyme's affinity for arsenate one order of magnitude. It is concluded that arsenate, after binding, promotes the same conformational change of the enzyme as that produced by P i.