DISTINCT STRUCTURAL IDENTITIES OF CATALYTIC AND CA-2-RETICULUM ATPASE( BINDING DOMAINS IN THE SARCOPLASMIC)

Electron microscopic visualization and diffraction patterns yield a pr ofile for the 110-kD SR ATPase, which includes a globular cytosolic re gion connected through a stalk to a membrane-bound region. Chemical de rivatization and mutagenesis demonstrate that the catalytic domain is located within the cytosolic region and the Ca2+ binding domain within the membrane-bound region. The catalytic domain of the Ca2+-ATPase an d of the Na+/K+-ATPase can be interchanged by chimeric recombination w ithout affecting the Ca2+ binding domain. Considerable detail of the A TPase folding pattern and functional structures is obtained by spectro scopic experiments and molecular modelling. The long-range functional linkage between the catalytic and Ca2+ binding domains appears to invo lve protein structural changes, most likely consisting of segmental re orientation with minimal alteration of secondary structure.