Dynamic structure of bovine adrenal cortex microsomal membranes studied by time-resolved fluorescence anisotropy of all-trans-1,6-diphenyl-1,3,5-hexatriene.

The motional properties of all-trans-1,6-diphenyl-1,3,5-hexatriene embedded in the microsomal membranes and in extracted lipid liposomes from bovine adrenal cortex are studied by fluorescence anisotropy decay measurements. The results demonstrate the existence of a nonvanishing value of the anisotropy (r infinity) in both systems. The r infinity values are significantly higher in the total membranes than in the protein-depleted liposomes, following the trend of the steady state anisotropy values previously reported (Gallay, J., Vincent, M., de Paillerets, C., Rogard, M., and Alfsen, A. (1981) J. Biol. Chem. 256, 1235-1241). This indicates that the depolarizing rotations of the probe are more restricted in the presence of proteins. No detectable effect of proteins on the reorientational correlation time can be observed. The temperature dependence of r infinity is not similar in both systems. In the complete membranes, a sharp decrease of r infinity value takes place between 27 and 32 degrees C, corresponding to 1/3 of the total curve of r infinity versus temperature is translated to lower temperatures. Thermal dependence of the reorientational correlation time is essentially the same in lipids and in complete membranes with an activation energy of 5 kcal mol-1. The results suggest that proteins play an essential role in organizing the deepest lipid region in the microsomal membranes from bovine adrenal cortex.