Excimer formation of ATPase from sarcoplasmic reticulum labeled with N-(3-pyrene)maleinimide

Sarcoplasmic reticulum ATPase from fast skeletal muscle was labeled in native vesicles with N-(3-pyrene)maleinimide. At labeling ratios larger than 1 mol pyrenemaleinimide/2.5 mol ATPase significant amounts of excimers are detected. Excimer concentration decreases at low, non-solubilizing amounts of detergents (0.2 mg X mg protein-1) and completely disappears after solubilization of the membranes. These results exclude that excimers are formed due to 'double-labeling' of one ATPase molecule. It is concluded that the ATPase exists as an oligomer within the membrane of native vesicles.