Proton spin-lattice relaxation of retinal rod outer segment membranes and liposomes of extracted phospholipids.

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Abstract
A large fraction of the phospholipid protons of bovine retinal rod outer segment (ROS) disc membrane vesicles yielded well-resolved NMR lines near physiological temperature. The spin-lattice (T1) relaxation rates of the resolved sharp resonance of ROS disc membranes appeared biphasic above 10.degree. C. The rate of the more rapidly relaxing component of each resonance closely matched the relaxation rate of the corresponding resonances of liposomes of purified ROS phospholipids. The slowly relaxing component of each disc membrane resonance was most likely due to phospholipids whose motion was affected by rhodopsin. The primary difference in the relaxation behavior of phospholipids in the ROS membrane vesicles and ROS liposomes appeared to be in T1, rather than T2, since the corresponding sharp resonances of both preparations have similar linewidths. The interaction of rhodopsin with the more fluid membrane phospholipids probably predominantly affects relatively high frequency segmental motions, which determine T1, while having minimal effects on the lower frequency segmental motions, which influence T2. This may be rationalized by assuming that a substantial fraction of the interacting phospholipids are relatively fluid with respect to less frequent, larger amplitude segmental motions, but that the more frequent segmental motions (such as .beta.-coupled trans-gauche isomerizations) are significantly restricted by interaction with protein.