STATIC AND TIME-RESOLVED STRUCTURAL STUDIES OF THE Ca2+-ATPase OF ISOLATED SARCOPLASMIC RETICULUM

Abstract

X-ray and neutron diffraction studies of oriented multilayers of isolated light sarcoplasmic reticulum (SR) have provided the separate profile structures of the lipid bilayer and the Ca2+-ATPase molecule within the membrane profile to approximately 10 A resolution. These studies utilized biosynthetically deuterated SR phospholipids incorporated isomorphously into the isolated SR membranes via exchange proteins. Time-resolved x-ray diffraction studies of these oriented SR membrane multilayers have indicated that significant changes occur in the membrane profile structure within a single turnover of the Ca2+-transport cycle. These studies utilized the flash photolysis of caged ATP to effectively synchronize the ensemble of Ca2+-ATPase molecules in the multilayer, synchrotron x-radiation to provide 100- to 500-millisecond data collection times, and double-beam spectrophotometry to monitor Ca2+ transport in the oriented SR membrane multilayer.