Abstract
Publisher Summary The X-ray and neutron diffraction studies of oriented multi-layers 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 ∼ 10A resolution. These studies utilized biosynthetically deuterated SR phospholipids incorporated isomorphously into the isolated SR membranes via exchange proteins. The nature of the time-resolved X-ray diffraction studies of the SR membrane can be summarized briefly as follows: the Ca2+- transport process is initiated essentially synchronously throughout the ensemble of Ca2+-ATPase molecules within an oriented multilayer of isolated SR membranes via the flash-photolysis of caged-adenosine triphosphate (ATP). The time-scale of the effective synchronization of the ensemble depends initially upon the duration of the UV light flash required to produce a sufficient quantity of ATP in the multilayer to sustain several turnovers of the Ca2+-ATPase molecules and is ultimately limited to the millisecond time-scale due to the kinetics of the dark-reactions of the photolysis process.
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