Intramolecular oscillation of the phosphorylation domain of rat cardiac sarcoplasmic reticulum titrated with arachidonoyl phosphatidylcholine.

Sarcoplasmic reticulum vesicles were prepared from rat myocardium. The intramolecular oscillation of the phosphorylation domain of Ca(2+)-ATPase in control vesicles and in vesicles titrated with diarachidonoyl phosphatidylcholine was studied with a nanosecond time-resolved fluorometer. The membrane viscosity of the lipid domain was decreased by the lipid titration. The phosphorylation domain was labeled with a fluorophore, anilinonaphthylmaleimide (ANM). The time course of anisotropy decay of ANM fluorescence reflects the localized oscillation in the protein structure. The half-decay time of the anisotropy was decreased by diarachidonoyl titration from 77 nsec in control vesicles to 66 nsec, suggesting an increase in the intramolecular oscillation. Concomitantly observed decreases in membrane viscosity and Ca(2+)-ATPase activity suggest that the decreased membrane viscosity destabilized the Ca(2+)-ATPase protein structure causing a reduction in Ca(2+)-ATPase activity.