A spin-label study of protein-lipid interaction in sarcoplasmic reticulum of rabbit skeletal muscle

Whether or not the thermotropic change at about 18 degrees C in the physical state of Ca2+-ATPase protein molecules of sarcoplasmic reticulum membranes could be transmitted to lipids through protein-lipid interactions was investigated using a spin-label technique. Fatty acid spin labels were used to probe the bulk membrane lipids while long-chain spin labels attached at one end to the Ca2+-ATPase molecules through a covalent bond were used to monitor the boundary lipids. The results on the temperature-dependence of alkyl-chain flexibility of lipid molecules indicate that the change in the state of the protein molecules is accompanied by one of the boundary lipids, but not of the bulk lipids.