Evidence for the cytoplasmic location of the N- and C-terminal segments of sarcoplasmic reticulum (Ca2+-Mg2+)-ATPase.

Antibodies were produced against 5 peptides corresponding to segments of the (Ca2+-Mg2+)-ATPase of fast-twitch rabbit skeletal muscle sarcoplasmic reticulum (SR) including the N- and C-terminal regions. With the exception of antibodies directed against the peptide corresponding to residues 567-582 all antibodies bound strongly to the ATPase in intact SR vesicles, indicating that the epitopes were located on the cytoplasmic face of the SR. When the vesicles were disrupted, by solubilisation in SDS, binding of these antibodies was unchanged, further supporting the idea that these epitopes were located on the cytoplasmic face of SR. This is the first demonstration of the location of the N- and C-terminal regions of SR (Ca2+-Mg2+)-ATPase. These observations are discussed in the light of current structural models of the ATPase.