Transfer of cholestane spin label between lipid bilayer membranes and its molecular motion in membranes

The relation between the molecular motion of a steroid in lipid membranes and the transfer rate between membranes was examined using radioactive cholestane spin label. Order parameters of the molecule were determined in bilayers composedof dipalmitoylglycerophosphocholine or egg yolk phosphatidylcholine at various temperatures. The line widths of the ESR signal of the cholestane spin label in membranes, which depend upon the rate of molecular axial rotation in the membranes, were also measured. The temperature dependences of these two parameters and of the transfer rate suggest a close correlation between the rate of molecular axial rotation and the transfer rate.