The membrane properties which control Ca2 ion uptake and ATPase activities by sarcoplasmic reticulum Ca2 ion-ATPase are investigated in a reconstituted vesicular bilayer system. The affinities of different lipids for binding sites on the enzyme are determined using a new fluorescence quenching method. The influence of pH and certain ions, especially calcium, on lipid behavior is examined using proton nuclear magnetic resonance (1HNMR) spectroscopy to detect individual lipids in a perdeuterated phospholipid matrix. It will then be possible to examine how enzyme activity and lipid binding to the enzyme can be influenced by electrostatic effects such as cation concentration and pH which have been implicated in pathological cardiac conditions.