STUDY OF ROTATIONAL MOBILITY OF E(1) AND E(2) CA2-ATPASE CONFORMERS IN SARCOPLASMIC-RETICULUM MEMBRANES USING TIME-RESOLVED PHOSPHORESCENCEANISOTROPY DECAY MEASUREMENTS()

Membrane preparations of sarcoplasmic reticulum Ca2+-ATPase from rabbi t skeletal muscles were covalently labeled with eosin 5'-isothiocyanat e at Lys-515 in the putative active site and with 5-(iodoacetamido)eos in, probably at Cys-670 and Cys-674. These preparations were used for measurements of laser-flash induced phosphorescence anisotropy in the microsecond time scale. An analysis of the influence of diethyl ether, glycerol, the nonionic detergent C(12)E(9), and Ca2+-ATPase ligands, which stabilize the enzyme in the E(1) or E(2) conformeric state, on t he anisotropy parameters have shown that Ca2+-ATPase in sarcoplasmic r eticulum membranes is present both in monomeric and oligomeric states. Enzyme transition from E(1) to E(2) conformation is connected with an increase of oligomeric complex content and their average size. This s upports the hypothesis that Ca2+-ATPase oligomeric state can be change d during reaction cycle of the enzyme.