Phospholipid exchange between restricted and nonrestricted domains in sarcoplasmic reticulum vesicles

Phosphorus nuclear magnetic resonance spectra of rabbit muscle light sarcoplasmic reticulum membranes consist of two overlapping resonances, one much broader than the other. The broad resonance arises from phospholipids motionally restricted, probably by association with the Ca2+-ATPase, while the narrow resonance arises from phospholipid only slightly perturbed by the presence of the protein. (Selinsky, B.S. and Yeagle, P.L. (1984) Biochemistry 23, 2281-2288). The rate of exchange between the two phospholipid domains represented by the resonances was determined by measuring the transfer of magnetization from the broad resonance to the narrow resonance. The rate of exchange of phospholipids from the restricted domain to the nonrestricted domain was determined to be 1 s-1.