[Application of ESR saturation transfer spectroscopy for the study of molecular mobility of membrane proteins]

The principles and possibilities of saturation transfer spectroscopy--a new approach in the spin label method, enabling one to measure rotational correlation times up to 10(-3) s--are briefly discussed. This approach is applied to the study of the molecular mobility of a membrane protein Ca-dependent ATPase in native sarcoplasmic reticulum membranes and in egg yolk and dipalmitoyllecithin proteoliposomes using spin labels selectively attached to different SH-groups of a protein. The mobility of the labels on two SH-groups was shown to be due to the intramolecular motion of the protein polar head. It is independent of the protein concentration in membrane but is sensitive to substrate binding and to lipid environment. The correlation of this mobility with the ATPase activity was observed when changing lipid environment and temperature.