Inhibitors bound to [Ca.sup.2}-free sarcoplasmic reticulum [Ca.sup.2}-ATPase lock its transmembrane region but not necessarily its cytosolic region, revealing the flexibility of the loops connecting transmembrane and cytosolic domains

A study was conducted to determine the effect of thapsigargin (TG) inhibitor on [Ca.sup.2}-free crystals of sarcoplasmic reticulum [Ca.sup.2}-ATPase. The findings reveal the flexibility of the loops connecting the transmembrane and cytosolic domains in the ATPase.