Spin-Label Studies of Rhodopsin-Lipid Interactions

Rhodopsin-lipid interactions have been studied in bovine rod outer segment (ROS) disk membranes by using a variety of freely diffusing spin-labels. Spin-labeled fatty acid, sterol and phospholipid molecules all display an apparent two-component ESR spectrum at temperatures below similar to 30 degree C. The narrow component constitutes 60-65% of the total spectral intensity and is very similar to that recorded for the same label in non-protein-containing lipid bilayers. The other, broader component is characteristic of a markedly more motionally restricted environment and is attributed to lipids interacting directly with the major protein rhodopsin of ROS disk membranes.