Calcium Pump ( ATPase ) of Sarcoplasmic Reticulum

Abstract

Ca 2+ ‐ATPase of sarcoplasmic reticulum is a membrane protein of 110 kDa and pumps Ca 2+ from the cytoplasm into the sarcoplasmic reticulum, an intracellular organelle, to relax muscle cells. Two Ca 2+ ions can be transported per ATP hydrolyzed and two or three protons are countertransported. The Ca 2+ ‐binding sites are located side by side in the transmembrane region. The crystal structures of this ATPase obtained for Ca 2+ ‐bound and unbound states show that large conformation changes take place during Ca 2+ binding and dissociation.