2H and 31P nuclear magnetic resonance studies of membranes containing bovine rhodopsin.

Purified, delipidated rhodopsin is recombined with phospholipid using octyl-glucoside (OG) and preformed vesicles. Normal egg phosphatidylcholine, phosphatidylcholine in which the N-methyl groups are fully deuterated, and dioleoyl phosphatidylcholine labeled with deuterium at carbons 9 and 10 were used. 31P nuclear magnetic resonance (NMR) and 2H NMR measurements were obtained of the pure phospholipids and of the recombined membranes containing rhodopsin. 31P NMR of the recombined membrane (containing the deuterated phospholipid) showed two overlapping resonances. One resembled a normal phospholipid bilayer, and the other was much broader, representing a motionally restricted phospholipid headgroup environment. The population of phospholipids in the motionally restricted environment can be modulated by conditions in the media. 2H NMR spectra of the same recombined membranes showed only one component. These experimental results agree with a theoretical analysis that predicts an insensitivity of 2H NMR to lipids bound to membrane proteins. A model containing at least three different phospholipid environments in the presence of the membrane protein rhodopsin is described.