31P-NMR studies of oriented multilayers formed from isolated sarcoplasmic reticulum and reconstituted sarcoplasmic reticulum.

31P-NMR spectra were obtained from oriented multilayer preparations of normal sarcoplasmic reticulum and reconstituted sarcoplasmic reticulum with lipid to protein ratios varying between 41 : 1 and 110 : 1. The dependence of the 31P-NMr spectra on the alignment of the membranes with respect to the magnetic field was used to draw two conclusions about the motion of the phospholipid molecules that contribute to the observed spectra. First, the phosphate group and the two adjacent methylene groups are able to rapidly rotate (i.e., tau R much less than 10-5 S) around the normal to the plane of the membrane. Second, the restricted internal motion of the phosphate group and the glycerol CH2OP group is very similar to that found in liposomes formed from sarcoplasmic reticulum phospholipids. Calibration experiments showed that all (100 +/- 7%) of the phospholipid molecules in the membrane can be accounted for in the observed spectra. Thus, essentially all the phospholipid molecules in the sarcoplasmic reticulum and the reconstituted sarcoplasmic reticulum membranes have the same motion in the polar headgroup region as found in model bilayer membranes. Since a large fraction of the phospholipid molecules (between one-quarter and one-half, depending on ;the lipid to protein ratio) are immediately surrounding the calcium-pump protein, we conclude that the calcium-pump protein does not perturb the motion of these 'boundary-layer' lipids.